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Defense Threat Reduction Agency

8725 John J. Kingman Road, MSC 6201

Fort Belvoir. VA 22060-6201

DTRA-TR.O74

Screening Doses for Induction of

Cancers Calculated with the

Interactive RadioEpidemiological

Program (IREP)

Approved for public release; distribution is unlimited.

March 2007

DTRA01-03-C-0064

David C. Kocher and

Julian A. Apostoaei

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Screening Doses for Induction of Cancers Calculated with the 

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14. ABSTRACT

This report presents tabulations of equivalent doses of ionizing radiation, referred to as screening doses, that 

correspond to an estimated probability of causation of specific cancers of approximately 50% at the upper 99% 

credibility limit. Screening doses for 32 cancer types were calculated with the Interactive RadioEpidemiological 

Program, which is used by the Department of Veterans Affairs in adjudicating claims for compensation for cancer by 

veterans of military services. 

15. SUBJECT TERMS

Nuclear Test Personnel Review, NTPR, Veteran, Atmospheric Nuclear Testing, Hiroshima Nagasaki Occupation, 

Cancer, Probability of Causation, PC, IREP 

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Dr. Paul K. Blake

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AG 703 767-2407

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iii

ABSTRACT

 This report presents tabulations of equivalent doses of ionizing radiation, referred to as 

screening doses, that correspond to an estimated probability of causation (PC) of specific cancers 

of approximately 50% at the upper 99% credibility limit. A PC of 50% at the upper 99% 

credibility limit is often used in evaluating whether it is at least as likely as not that a given 

cancer in an individual was caused by exposure to ionizing radiation for purposes of adjudicating 

claims for compensation. Screening doses for 32 cancer types were calculated with the 

Interactive RadioEpidemiological Program (IREP), which is used by the Department of Veterans 

Affairs (VA) in adjudicating claims for compensation for cancer by veterans of military services. 

Screening doses calculated with IREP take into account uncertainties in estimating cancer risk 

and PC associated with given equivalent doses to organs or tissues in which cancers occur. 

Except for cancers that occur only in females and breast cancer in females, tabulated screening 

doses apply to males. Screening doses for most cancer types depend on an individual’s age at 

exposure and age at the time of diagnosis of cancer. Screening doses for lung cancer also depend 

on an individual’s smoking history, and screening doses for skin cancers depend on an 

individual’s race or ethnicity. Screening doses calculated with IREP are compared with 

screening doses for a limited number of cancer types calculated previously by the Committee on 

Interagency Radiation Research and Policy Coordination (CIRRPC), which were used by VA for 

many years in adjudicating claims for compensation. Screening doses calculated with IREP are 

higher than the corresponding values obtained from the CIRRPC table for most combinations of 

cancer type, age at exposure, and age at diagnosis. An analysis of the accuracy of screening 

doses calculated with IREP and tabulated in this report indicates that they could differ from 

equivalent doses that correspond to an upper 99% credibility limit of PC of exactly 50% by less 

than ±10% for most cancer types, ages at exposure, and ages at diagnosis of concern in VA 

radiation claims. Inaccuracies in screening doses are due to the randomness of statistical 

sampling in the method of uncertainty analysis used in IREP. 
iv

TABLE OF CONTENTS

ABSTRACT................................................................................................................................... iii 

LIST OF TABLES...........................................................................................................................v 

LIST OF FIGURES ..................................................................................................................... viii 

1. INTRODUCTION ......................................................................................................................1 

2. APPROACHES TO EVALUATING CAUSATION OF CANCERS .......................................4 

2.1 Description and Estimation of Probability of Causation ..............................................4 

2.2 Evaluation of Causation of Cancers Using CIRRPC Table..........................................6 

2.3 Evaluation of Causation of Cancers Using IREP .........................................................7 

3. CANCER RISK MODELS INCORPORATED IN IREP........................................................11 

3.1 Categories of Cancer Risk Models .............................................................................11 

3.1.1 Group 1 Cancers........................................................................................12 

3.1.2 Group 2 Cancers........................................................................................12 

3.1.3 Group 3 Cancers........................................................................................13 

3.1.4 Risk Models for Lung Cancer....................................................................13 

3.1.5 Group 4 Cancers........................................................................................14 

3.2 Minimum Latency Period for Different Cancer Types...............................................15 

4. SCREENING DOSES CALCULATED WITH IREP..............................................................19 

4.1 Tabulation and Discussion of Screening Doses..........................................................19 

4.1.1 Calculation of Screening Doses.................................................................19 

4.1.2 Accuracy of Calculated Screening Doses..................................................21 

4.1.3 Discussion of Screening Doses..................................................................25 

4.2 Comparison with Screening Doses in CIRRPC Table................................................27 

4.3 Application of Screening Doses..................................................................................29 

4.3.1 Exposure to Multiple Radiation Types.......................................................29 

4.3.2 Exposures in More Than One Year............................................................31 

4.4 Summary Discussion of Calculated Screening Doses ................................................33 

REFERENCES ..............................................................................................................................71 

DISTRIBUTION LIST......................................................................................73 
v

LIST OF TABLES

Table 2-1. Screening doses (rem) for specific cancer types calculated by CIRRPC (1988) and 

used by VA in adjudicating claims for compensation for radiation-induced cancer...........9 

Table 3-1. Categories of cancer risk models incorporated in IREP..............................................17 

Table 4-1. Screening doses (rem) calculated with IREP: Cancers of oral cavity and pharynx 

(including lip).....................................................................................................................35 

Table 4-2. Screening doses (rem) calculated with IREP: Cancer of esophagus...........................36 

Table 4-3. Screening doses (rem) calculated with IREP: Cancer of stomach ..............................37 

Table 4-4. Screening doses (rem) calculated with IREP: Cancer of colon...................................38 

Table 4-5. Screening doses (rem) calculated with IREP: Cancer of rectum (including anus 

 and anal canal) ...................................................................................................................39 

Table 4-6. Screening doses (rem) calculated with IREP: Cancers of digestive tract other 

 than stomach, colon, and rectum........................................................................................40 

Table 4-7. Screening doses (rem) calculated with IREP: Cancer of liver (including biliary 

 system) ...............................................................................................................................41 

Table 4-8. Screening doses (rem) calculated with IREP: Cancer of gallbladder (including 

 bile ducts)...........................................................................................................................42 

Table 4-9. Screening doses (rem) calculated with IREP: Cancer of pancreas..............................43 

Table 4-10. Screening doses (rem) calculated with IREP: Cancer of lung (including trachea 

 and bronchus) – I ...............................................................................................................44 

Table 4-11. Screening doses (rem) calculated with IREP: Cancer of lung (including trachea 

 and bronchus) – II ..............................................................................................................45 

Table 4-12. Screening doses (rem) calculated with IREP: Cancers of respiratory tract other 

 than lung.............................................................................................................................46 

Table 4-13. Screening doses (rem) calculated with IREP: Cancer of bone..................................47 
vi

LIST OF TABLES (continued) 

Table 4-14. Screening doses (rem) calculated with IREP: Cancers of connective tissue 

 (including soft tissue not listed).........................................................................................48 

Table 4-15. Screening doses (rem) calculated with IREP: Malignant melanoma of skin ............49 

Table 4-16. Screening doses (rem) calculated with IREP: Basal cell carcinoma of skin.............50 

Table 4-17. Screening doses (rem) calculated with IREP: Squamous cell carcinoma of skin .....51 

Table 4-18. Screening doses (rem) calculated with IREP: Cancer of breast (female) .................52 

Table 4-19. Screening doses (rem) calculated with IREP: Cancer of breast (male).....................53 

Table 4-20. Screening doses (rem) calculated with IREP: Cancer of ovary ................................54 

Table 4-21. Screening doses (rem) calculated with IREP: Cancers of all female genitalia 

 other than ovary .................................................................................................................55 

Table 4-22. Screening doses (rem) calculated with IREP: Cancers of all male genitalia 

 (including prostate) ............................................................................................................56 

Table 4-23. Screening doses (rem) calculated with IREP: Cancer of bladder..............................57 

Table 4-24. Screening doses (rem) calculated with IREP: Cancers of kidney and other 

 urinary organs except bladder............................................................................................58 

Table 4-25. Screening doses (rem) calculated with IREP: Cancer of eye....................................59 

Table 4-26. Screening doses (rem) calculated with IREP: Cancers of nervous system 

 (including brain).................................................................................................................60 

Table 4-27. Screening doses (rem) calculated with IREP: Cancer of thyroid..............................61 

Table 4-28. Screening doses (rem) calculated with IREP: Cancers of endocrine glands 

 other than thyroid...............................................................................................................62 

Table 4-29. Screening doses (rem) calculated with IREP: Cancers of other and ill-defined 

 sites ....................................................................................................................................63 
vii

LIST OF TABLES (continued) 

Table 4-30. Screening doses (rem) calculated with IREP: Lymphoma and multiple 

 myeloma.............................................................................................................................64 

Table 4-31. Screening doses (rem) calculated with IREP: All leukemia excluding chronic 

 lymphocytic leukemia (CLL).............................................................................................65 

Table 4-32. Screening doses (rem) calculated with IREP: Chronic myeloid leukemia 

 (CML) ................................................................................................................................66 

Table 4-33. Screening doses (rem) calculated with IREP: Acute lymphocytic leukemia 

 (ALL) .................................................................................................................................67 

Table 4-34. Screening doses (rem) calculated with IREP: Acute myeloid leukemia (AML) ......68 

Table 4-35. Lowest screening doses (rem) for any age at exposure and time since exposure 

 when cancer is diagnosed for all cancer types calculated with IREP................................69 
viii

LIST OF FIGURES

Figure 3-1. S-shaped (sigmoid) function assumed in IREP to represent effect of minimum 

 latency period on reducing risks of all solid cancers except thyroid and bone cancer at 

 early times since exposure and its uncertainty...................................................................18 
 1

1. INTRODUCTION

 The Department of Veterans Affairs (VA) is responsible for adjudicating claims for 

compensation for cancers that occur in veterans of military services who were exposed to 

ionizing radiation.1

 In some cases, adjudication of a claim takes into account estimates of 

radiation dose to an organ or tissue in which a cancer occurred that are developed by the Defense 

Threat Reduction Agency (DTRA). In all such cases, VA uses estimated upper bounds of 

equivalent doses2

 provided by DTRA and other information to develop a medical opinion on 

whether a veteran’s cancer was caused by ionizing radiation. Upper bounds of equivalent doses 

are intended to be at least upper 95% credibility limits when uncertainties in estimating 

equivalent doses to an organ or tissue of concern are taken into account. Compensation usually 

is awarded if VA concludes that it is at least as likely as not that a veteran’s cancer was caused 

by radiation (i.e., the probability is at least 50%). VA gives claimants the benefit of the doubt by 

interpreting “at least as likely as not” to mean that the probability of causation (PC) should be at 

least 50% at the upper 99% credibility limit when uncertainties in estimating cancer risk and PC 

associated with upper-bound estimates of equivalent doses are taken into account. Thus, VA 

usually awards compensation when there is at least a 1% chance that PC is 50% or greater. An 

upper 99% credibility limit of PC of at least 50% also is used in evaluating causation of cancers 

in the Department of Labor’s compensation program for workers at Department of Energy 

facilities (EEOICPA 2000; DHHS 2002). 

 The most common circumstance that requires VA to use estimates of radiation dose 

provided by DTRA in adjudicating claims for compensation involves cancers that are not one of 

 1

Radiation-exposed veterans of concern to this report are specified in VA regulations [38 CFR 

3.309(d)(3)]. They include participants in the atmospheric nuclear-weapons testing program between 

1945 and 1962 and occupation forces or prisoners of war in Hiroshima or Nagasaki, Japan, after the 

atomic bombings in 1945. Diseases other than cancer that could be caused by exposure to ionizing 

radiation (e.g., cataract of the lens of the eye) are not considered in this report. 

2

As defined by the International Commission on Radiological Protection (ICRP 1991), equivalent 

dose is an average absorbed dose to an organ or tissue of concern modified by a prescribed radiation 

weighting factor (wR) for the radiation type that delivers the dose. Equivalent dose was previously called 

“dose equivalent” by DTRA. 
 2

21 cancers that are specified as “presumptive” diseases in VA regulations [38 CFR 3.309(d)(2)]. 

A presumptive disease is assumed to be service-connected, without regard for the dose received, 

if adequate proof of participation in a radiation-risk activity is provided. Claims for 

compensation for cancers that are not presumptive diseases are adjudicated under VA regulations 

for “nonpresumptive” diseases [38 CFR 3.311]. In all such cases, VA uses estimated upper 

bounds of equivalent doses provided by DTRA in developing a medical opinion on whether it is 

at least as likely as not that a veteran’s cancer was caused by radiation.3

 Skin and prostate cancer 

are the most common nonpresumptive cancers in claims of concern to this report. 

 VA currently uses computer software called the Interactive RadioEpidemiological 

Program (IREP) (Land et al. 2003; NIOSH 2002) when it is necessary to evaluate whether a 

veteran’s cancer was caused by exposure to ionizing radiation (Mansfield 2005). VA uses IREP 

to calculate a probability distribution of PC associated with a veteran’s upper-bound estimates of 

equivalent doses, ages at times of exposure, and age at the time of diagnosis of cancer. 

Probability distributions of PC calculated by IREP take into account uncertainties in estimating 

an individual’s risk of cancer due to radiation exposure and associated PC. VA then compares 

the upper 99% credibility limit of the probability distribution of PC with the value 50% in 

evaluating whether it is at least as likely as not that the veteran’s cancer was caused by radiation. 

 VA’s current policy of using an upper 99% credibility limit of PC calculated with IREP 

in evaluating causation of cancers superseded a policy adopted in the late 1980s of using a table 

of equivalent doses that also corresponded to an estimated upper 99% credibility limit of PC of 

50% for a limited number of cancer types. That table was developed by the Committee on 

Interagency Radiation Research and Policy Coordination (CIRRPC 1988) on the basis of data on 

risks of cancers that were considered to be radiogenic at the time (NIH 1985). Equivalent doses 

in the CIRRPC table were referred to as “screening doses,” and the same terminology is used in 

this report to denote equivalent doses that correspond to an estimated upper 99% credibility limit 

 3

In other, less common circumstances, VA is required to use estimates of radiation dose in 

adjudicating claims for compensation for any of the 21 cancers that are presumptive diseases. Estimates 

of dose must be used if adequate proof of participation in a radiation-risk activity while in service is not 

available, or if a claimant is seeking compensation to cover a time period prior to the time the veteran’s 

cancer was declared to be presumptive in VA regulations. In all such cases, a claim is adjudicated under 

the regulations for nonpresumptive diseases. 
 3

of PC of approximately 50%. For more than a year prior to adopting a policy of using IREP 

exclusively, VA evaluated causation of cancers using the CIRRPC table and IREP in parallel 

when a cancer of concern was included in the CIRRPC table. In all such cases, the method that 

was more favorable to the claimant was used in adjudicating a claim (VHA/OPHEH 2003; 

Mather and Otchin 2004). 

 The primary purpose of this report is to present tabulations of screening doses for many 

cancer types that we calculated with IREP. Again, a screening dose is an equivalent dose that 

corresponds to an estimated upper 99% credibility limit of PC of approximately 50% when 

uncertainties in estimating cancer risk and PC associated with given equivalent doses to an organ 

or tissue in which a cancer occurred are taken into account. Screening doses calculated with 

IREP also are compared with screening doses for the limited number of cancer types given in the 

CIRRPC table, as used previously by VA. 

 The following section describes how PC is estimated, and it discusses VA’s use of the 

CIRRPC table and IREP to evaluate causation of cancers on the basis of estimates of equivalent 

dose to an organ or tissue in which a cancer occurred. Section 3 describes models incorporated 

in IREP to estimate risks of different cancer types due to exposure to ionizing radiation. 

Information on risk models is intended to be helpful in understanding how screening doses 

calculated with IREP depend on an individual’s age at exposure and age at the time of diagnosis 

of cancer. Section 4 describes the assumptions used to calculate screening doses and presents 

tabulations and discussions of screening doses, as well as comparisons with screening doses in 

the CIRRPC table. An evaluation of the accuracy of screening doses tabulated in this report also 

is presented. This evaluation is based on the consideration that screening doses calculated with 

IREP generally do not correspond to an upper 99% credibility limit of PC of exactly 50%. 

Inaccuracies in screening doses calculated with IREP are due to the randomness of statistical 

sampling in the method used to estimate uncertainty in cancer risk and PC. 
 4

2. APPROACHES TO EVALUATING CAUSATION OF CANCERS

 This section presents an overview of approaches to evaluating causation of cancers in 

individuals who were exposed to ionizing radiation. Section 2.1 describes how PC is estimated 

and how PC depends on dose. Sections 2.2 and 2.3 discuss the two approaches (i.e., the 

CIRRPC table and IREP) that have been used by VA in evaluating causation of cancers in 

veterans who were exposed to radiation. 

2.1 Description and Estimation of Probability of Causation

 The term “probability of causation” refers to the probability that a diagnosed cancer in an 

individual was caused by prior exposure to ionizing radiation.4

 PC is defined as: 

 R B

R PC

+ = , (1) 

where R is the risk (probability) of the cancer of concern due to radiation exposure and B is the 

baseline (background) risk of that cancer due to all other causes. Risks of most cancers due to 

radiation exposure are assumed to depend on sex, age at exposure, and attained age (age at a 

given time); baseline risks generally depend on sex and attained age. Although PC is related to 

risk and is also a probability, there is an essential difference: whereas risk is the probability that a 

radiation-induced cancer will occur at some time after an exposure in an individual who is free of 

that cancer, PC is conditional on the occurrence of cancer. 

 In IREP, PC is calculated on the basis of an estimate of the excess relative risk (ERR) 

associated with a given radiation dose to an organ or tissue in which a cancer occurred (Land et 

al. 2003). ERR is calculated as: 

 4

PC is referred to as “assigned share” by Land et al. (2003) to indicate that it is calculated on the 

basis of estimates of cancer risks obtained in epidemiological studies of exposed populations. Thus, PC is 

a property of a group to which an individual belongs that is assigned to that individual; it may not be the 

true PC for that individual. 
 5

 ERR = RR – 1 , (2) 

where RR is the relative risk, defined as the risk in an exposed population relative to the risk in a 

similar unexposed population, given by: 

 R

R B RR + = , (3) 

Thus, using the definition in eq. (1) and the relations in eqs. (2) and (3), PC is estimated as: 

 ERR 1

ERR PC

+ = . (4) 

Although PC is a probability and, thus, has a value between 0 and 1, we express PC in percent 

(e.g., a PC of 0.5 is expressed as 50%) to be consistent with output from IREP. 

 For any cancer type, ERR is assumed to be an increasing function of dose, without 

threshold. Risk models for all cancer types incorporated in IREP, except for leukemia under 

conditions of acute exposure to low-LET radiations (photons or electrons), assume that ERR is a 

linear function of dose (Land et al. 2003). Thus, in most cases, PC is estimated as: 

 (α ) 1

α PC

× +

× = DD , (5) 

where α is the ERR per unit equivalent dose for a cancer type of concern and D is the equivalent 

dose to the organ or tissue where that cancer occurs. Risk models for all types of leukemia under 

conditions of acute exposure to low-LET radiations assume that ERR is a linear-quadratic 

function of dose given by α(D + D2

) (Land et al. 2003), and PC in these cases is estimated as: 

 [(α ( )] 1

α ( ) PC 2

2

× + +

× + = D DD D . (6) 
 6

Thus, for any cancer type, PC is a nonlinear function of dose, and the dose corresponding to a 

given PC increases nonlinearly as the risk, R, and ERR associated with radiation exposure 

decrease, and vice versa. 

2.2 Evaluation of Causation of Cancers Using CIRRPC Table

 From the late 1980s until April 2005, VA evaluated causation of some cancers in 

veterans who were exposed to ionizing radiation using a table of screening doses that was 

developed by CIRRPC (1988); the CIRRPC table of screening doses, which correspond to an 

estimated upper 99% credibility limit of PC of 50%, is reproduced in Table 2-1. If an estimated 

upper bound of the total equivalent dose to an organ or tissue in which a cancer occurred, as 

provided by DTRA, equaled or exceeded the screening dose obtained from the CIRRPC table 

that applied to the veteran of concern, VA usually rendered a favorable medical opinion.5

 

Screening doses in the CIRRPC table were calculated on the basis of estimates of PC at various 

equivalent doses obtained from the 1985 Radioepidemiological Tables (NIH 1985)6

 and 

estimates of uncertainty in cancer risks associated with given equivalent doses in each organ or 

tissue of concern (CIRRPC 1988). Cancer types for which screening doses were given in the 

CIRRPC table are those that were considered to be radiogenic on the basis of a statistically 

significant dose-response in Japanese atomic-bomb survivors and other study populations (NIH 

1985). It should be noted that VA did not actually estimate PC when screening doses obtained 

from the CIRRPC table were used in evaluating causation of cancer. 

 5

Comparison of an estimated upper bound of the total equivalent dose with the applicable 

screening dose obtained from the CIRRPC table was not the only factor that could be considered by VA 

in formulating a medical opinion on causation of a veteran’s cancer. For example, information on a 

veteran’s history of exposure to ionizing radiation and other carcinogens at times other than during 

participation in a radiation-risk activity also could be considered. Similar considerations apply to VA’s 

use of IREP. However, VA has rarely based its medical opinions on causation of cancer on factors other 

than screening doses obtained from Table 2-1 or estimates of upper 99% credibility limits of PC 

calculated with IREP (N. Otchin, Department of Veterans Affairs, personal communication). 

6

The 1985 Radioepidemiological Tables were based on cancer risk models that were developed in 

the BEIR III report (NRC, 1980) on the basis of data obtained from studies of Japanese atomic-bomb 

survivors and medical patients who had been exposed mainly to x rays or high-energy gamma rays. 
 7

 The following points about screening doses in the CIRRPC table are of interest. First, for 

all cancer types considered, screening doses increased with increasing age at exposure from 

age 20 to 40 and remained constant thereafter. Those increases were based on data which 

indicated that risks due to radiation exposure relative to baseline risks declined with increasing 

age at exposure (NRC 1980). Second, for all cancer types except leukemia, screening doses 

were independent of the time since exposure when cancer was diagnosed, provided the time 

between exposure and diagnosis exceeded an assumed minimum latency period. Finally, 

screening doses for the various types of leukemia were higher at times since exposure when 

cancer was diagnosed of 20 years or more than at times between exposure and diagnosis less 

than 20 years. The assumed dependencies on time since exposure were based on data which 

indicated that risks of radiation-induced leukemia declined nearly to baseline levels at times 

beyond a few decades after exposure (NRC 1980). 

 The CIRRPC table did not include screening doses for some cancer types for which an 

estimate of radiation dose was required in adjudicating claims for compensation. Important 

examples include skin and prostate cancer. Prior to 2003, VA formulated a medical opinion on 

causation of such cancers on the basis of information obtained from the medical or 

epidemiological literature or information provided by the physician who diagnosed the cancer. 

For example, beginning in the late 1990s, VA evaluated causation of basal cell carcinoma (the 

most common type of skin cancer) on the basis of an estimate of the lowest equivalent dose at 

which an excess of that cancer type had been observed in epidemiological studies. That dose 

was about 9 rem (NRC 1990). 

2.3 Evaluation of Causation of Cancers Using IREP

 In 2003, VA began using IREP in parallel with the CIRRPC table when an evaluation of 

causation of cancers was required (VHA/OPHEH 2003; Mather and Otchin 2004), and a policy 

of using IREP exclusively was adopted in April 2005 (Mansfield 2005). IREP was developed to 

update and replace the 1985 Radioepidemiological Tables, which provided the basis for 

screening doses in the CIRRPC table. 
 8

 In contrast to the CIRRPC table, IREP assumes that all cancers except chronic 

lymphocytic leukemia (CLL) are radiogenic, including cancers that show only a weak 

association with exposure to ionizing radiation in Japanese atomic-bomb survivors (Land et al. 

2003). IREP also incorporates more recent data on cancer risks due to exposure to ionizing 

radiation and revised models to estimate ERRs associated with given equivalent doses to specific 

organs or tissues (Land et al. 2003). IREP calculates a probability distribution of PC associated 

with given equivalent doses to an organ or tissue in which a cancer occurred. Probability 

distributions of PC take into account several sources of uncertainty in estimating ERR associated 

with an individual’s radiation exposure, as well as uncertainties in estimated equivalent doses if 

they are included in input to a calculation.7

 Probability distributions of PC calculated with IREP 

include an upper 99% credibility limit, which VA compares with the value 50% for the purpose 

of evaluating causation of cancer in veterans who were exposed to ionizing radiation. 

 7

VA does not use uncertainties in estimated equivalent doses provided by DTRA in evaluating 

causation of cancers. Rather, in accordance with VA regulations [38 CFR 3.311(a)(1)], only estimated 

upper bounds of equivalent doses, which are intended to be at least upper 95% credibility limits, are used 

in adjudicating claims for compensation. This approach usually results in a higher estimate of the upper 

99% credibility limit of PC than would be obtained by using probability distributions of equivalent doses 

as input to a calculation. Exceptions could occur only when the uncertainty in the dose is larger than 

other uncertainties in estimating ERR associated with an individual’s given doses. Statistical 

uncertainties in estimating ERRs in Japanese atomic-bomb survivors and other study populations on the 

basis of fits to data on dose-response are always important, and uncertainties in transferring ERRs in 

atomic-bomb survivors to the U.S. population are important for many cancers. 
 9

Table 2-1. Screening doses (rem) for specific cancer types calculated by CIRRPC (1988) 

and used by VA in adjudicating claims for compensation for radiation-induced cancera

 Age at exposure (y) 

Type of cancer < 20 30 > 40 

Chronic granulocytic leukemiab 

 Within 20 years of exposurec 0.9 1.3 1.4 

 20 or more years post-exposurec

 2.7 3.2 5.9 

Acute leukemiab

 

 Within 20 years of exposurec

 1.1 1.8 4.1 

 20 or more years post-exposurec

 3.5 4.1 5.5 

Leukemia (excluding chronic lymphatic)b,d

 

 Within 20 years of exposurec

 1.1 1.7 3.3 

 20 or more years post-exposurec

 3.3 3.9 5.5 

Colon cancer 17.0 33.1 58.1 

Esophageal cancer 3.9 9.9 16.7 

Female breast cancer 18.8 37.0 78.6 

Kidney and bladder cancer 13.4 23.1 34.7 

Liver cancer 1.0 3.3 8.2 

Lung cancer 

 Known smokerse

 25.5 48.8 72.1 

 Othersf

 4.3 9.3 15.0 

Pancreatic cancer 5.8 13.7 24.3 

Stomach cancer 6.9 13.8 23.2 

Thyroid cancer 3.3 7.4 8.8 

 See following page for footnotes to table. 
 10

Footnotes to Table 2-1

____________________ 

a

Adapted from Table 3 of CIRRPC (1988). Screening doses were developed on the basis of the 

1985 Radioepidemiological Tables (NIH 1985) for cancer types that were considered to be radiogenic. 

Screening doses corresponded to an estimated upper 99% credibility limit of PC of 50% when 

uncertainties in estimating cancer risks associated with given equivalent doses in each organ or tissue of 

concern were taken into account. Screening doses for ages at exposure between 20 and 30 years or 30 

and 40 years should be obtained by linear interpolation. 

b

Dose to active bone marrow. 

c

Time since exposure when cancer was diagnosed. 

d

Cancer type refers to all leukemia as a group and was assumed when the diagnosed leukemia 

was not a particular type listed separately. e

Category applied when the veteran was known to have been a regular smoker (10 or more 

cigarettes per day) within five years of diagnosis. Screening doses were calculated by assuming that the 

veteran was a member of an average U.S. population that included smokers and nonsmokers. 

f

Category applied when the veteran’s smoking habits were unknown, the veteran was known to 

have stopped smoking five years or more before diagnosis, or the veteran was known to be a nonsmoker. 

Screening doses were calculated by assuming that the veteran was a nonsmoker. 
 11

3. CANCER RISK MODELS INCORPORATED IN IREP

 This section describes models incorporated in IREP to estimate ERRs for specific cancers 

that are associated with given doses of ionizing radiation to organs or tissues in which those 

cancers occur. These discussions are intended to be helpful in understanding how screening 

doses calculated with IREP depend on an individual’s age at exposure and age at diagnosis. Risk 

models for all cancer types are described in detail elsewhere (Land et al. 2003; NIOSH 2002). 

Except as noted, risk models discussed in this section are incorporated in versions of IREP that 

were developed by the National Institute for Occupational Safety and Health (NIOSH) for use in 

the Department of Labor’s compensation program for workers at Department of Energy 

facilities. Versions of IREP developed by NIOSH have been used by VA in evaluating causation 

of cancers in veterans who were exposed to ionizing radiation. 

3.1 Categories of Cancer Risk Models

 Cancer risk models incorporated in IREP are categorized into four groups, as summarized 

in Table 3-1. Use of a variety of risk models for cancer types other than leukemia contrasts with 

models for those cancer types incorporated in CIRRPC screening doses, which assumed that 

risks decrease with increasing age at exposure from age 20 to 40 but are independent of attained 

age (NIH 1985). Another difference involves assumed dependencies of cancer risks on dose. In 

IREP, a linear relationship between dose and risk is assumed, except a linear-quadratic 

relationship is assumed for all types of leukemia under conditions of acute exposure to low-LET 

radiations (Land et al. 2003). In risk models that were used to calculate screening doses in the 

CIRRPC table, a linear dose-response relationship was assumed for breast and thyroid cancer but 

a linear-quadratic relationship was assumed for all other cancer types (NIH 1985). 

 Risk models for cancer types in each category are discussed in the following sections, 

except the model for lung cancer due to exposure to radon (Group 4) is not discussed because 

exposure to radon is not a concern in VA radiation claims. An implicit assumption in these 

discussions is that the time since exposure is sufficiently long that the minimum latency period 
 12

does not have a significant effect on estimated risks. Assumptions in IREP about the minimum 

latency period for each cancer type are discussed in Section 3.2. 

3.1.1 Group 1 Cancers

 For cancer types in Group 1, ERR is assumed to depend on age at exposure and attained 

age. For a given age at exposure, ERR decreases linearly with increasing attained age to age 50 

and remains constant thereafter. For a given attained age, ERR decreases exponentially between 

ages at exposure of 15 and 30 and remains constant outside that interval. The model includes a 

cancer-specific parameter to modify the assumed linear dose-response relationship, and 

dependencies of ERR on age at exposure and attained age are modified by parameters that also 

are assumed to be cancer-specific. The various model parameters are assumed to be strongly 

correlated on the basis of data for the relatively large number of cases of these cancer types in 

Japanese atomic-bomb survivors. The model for breast cancer is based on data in females and is 

assumed to apply to males as well. 

In modeling the dose-response for cancer types in Group 1 in Japanese atomic-bomb 

survivors, only ERRs for all digestive cancers other than stomach, colon, and rectum are 

assumed to depend on sex; ERRs for liver cancer are the same in males and females. However, 

in applying estimated ERRs for liver cancer, as well as breast cancer in females, to the U.S. 

population, sex-specific baseline risks were taken into account (Land et al. 2003). 

3.1.2 Group 2 Cancers

 The risk model for cancer types in Group 2 is similar to the model for Group 1 cancers. 

Specifically, ERR for a given age at exposure decreases linearly with increasing attained age to 

age 50 and remains constant thereafter, and ERR for a given attained age decreases exponentially 

between ages at exposure of 15 and 30 and remains constant outside that interval. However, 

because there have been fewer cases of Group 2 cancers in Japanese atomic-bomb survivors, the 

cancer-specific parameter that modifies the assumed linear dose-response relationship was found 
 13

to be practically independent of cancer-specific parameters that modify the assumed 

dependencies of ERR on age at exposure and attained age (Land et al. 2003). Therefore, the 

model for Group 1 cancers is replaced by an approximation in which the parameters that modify 

the dependencies of ERR on age at exposure and attained age are assumed to be the same for all 

cancer types. The model for lung cancer in Group 2 also depends on an individual’s smoking 

history.8

 As discussed in the following two sections, an alternative model for lung cancer in 

Group 3 is included in the version of IREP currently used by NIOSH. 

 For all cancer types in Group 2 that occur in males and females, ERRs in Japanese 

atomic-bomb survivors are assumed to depend on sex (Land et al. 2003). As with all cancer 

types in Group 1, sex-specific baseline risks were taken into account in transferring ERRs in 

atomic-bomb survivors to the U.S. population. 

3.1.3 Group 3 Cancers

 For cancer types in Group 3, ERR is assumed to be independent of age at exposure and 

attained age. A dependence of ERR on sex similar to the sex-dependence in the risk model for 

cancer types in Group 2 is assumed in the model for lung cancer in Group 3. 

3.1.4 Risk Models for Lung Cancer

 As indicated in Table 3-1, two different risk models for lung cancer are incorporated in 

the version of IREP currently used by VA. In the model described by NIOSH (2002), ERR for 

lung cancer is assumed to be independent of age at exposure and attained age, and lung cancer is 

included in Group 3. In the model developed more recently by the National Institutes of Health 

(NIH), ERR for lung cancer is assumed to depend on age at exposure and attained age (Land et 

al. 2003), and lung cancer is included in Group 2. In addition, although both models use the 

 8

In cases of exposure to sources other than radon, IREP calculates ERRs for lung cancer for the 

following smoking categories: never-smokers, former smokers, current smokers with an unspecified 

consumption rate of cigarettes, and four categories of current smokers defined by the number of cigarettes 

smoked per day. 
 14

same categories of smoking history for an exposed individual, the two models use somewhat 

different approaches to calculating ERR in the different categories.9

 The version of IREP currently used by VA calculates PC using both models for lung 

cancer, and the higher estimate of PC at the upper 99% credibility limit is emphasized in the 

output from IREP. As indicated by screening doses tabulated in this report, the model that gives 

the higher upper 99% credibility limit of PC depends on smoking history and the time since 

exposure when cancer was diagnosed (see Section 4.1.3). 

3.1.5 Group 4 Cancers

 Cancer types in Group 4 each have a unique risk model. The model for each cancer type 

in this group is described in the following paragraphs. 

 Two models are assumed for skin cancers. ERRs for basal cell carcinoma decrease 

exponentially with increasing age at exposure to age 40 and remain constant thereafter, but are 

independent of attained age; the model for basal cell carcinoma also is applied to malignant 

melanoma, for which there were too few cases in Japanese atomic-bomb survivors to establish a 

dose-response relationship (Land et al. 2003). ERRs for non-melanoma skin cancers other than 

basal cell carcinoma (e.g., squamous cell carcinoma) are independent of age at exposure and 

attained age. ERRs for all skin cancers are independent of sex but depend on race or ethnicity.10 

Differences in baseline risks of skin cancers in different racial and ethnic groups are taken into 

account in the transfer of ERRs in Japanese atomic-bomb survivors to the U.S. population. 

 ERR for thyroid cancer decreases exponentially with increasing age at exposure to age 50 

and remains constant thereafter, but is independent of attained age and sex. 

 9

The two models estimate ERR for lung cancer using the same smoking-related adjustment 

factors but apply them differently. In the model for lung cancer in Group 3, adjustments for smoking 

history are applied to an estimated ERR that is an average over all smoking categories. In the model for 

lung cancer in Group 2, those adjustments are applied to an estimated ERR in never-smokers only. 

10IREP calculates ERRs for skin cancers for the following racial or ethnic groups: American 

Indians or Alaska natives; Asians, native Hawaiians, or other Pacific islanders; blacks; white Hispanics; 

and white non-Hispanics. ERRs for all other cancer types are assumed to be independent of race or 

ethnicity. 
 15

 ERR for all leukemia as a group, excluding CLL,11 decreases exponentially with 

increasing age at exposure to age 55 and increasing time since exposure to 50 years, and remains 

constant thereafter. The effect of time since exposure on ERR is similar to the effect that is 

incorporated in screening doses for various types of leukemia in the CIRRPC table (see 

Section 2.2). Modifications of this model are used for specific types of leukemia. ERRs for 

acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) are independent of age at 

exposure, and the exponential decrease in ERR for CML with increasing time since exposure is 

faster in males than in females. ERR for acute lymphocytic leukemia (ALL) decreases 

exponentially with increasing time since exposure when exposure occurs before age 20, but is 

independent of time since exposure when exposure occurs at age 20 or beyond. ERRs for AML, 

ALL, and all leukemia as a group are independent of sex. 

3.2 Minimum Latency Period for Different Cancer Types

 Descriptions of risk models for different cancer types in Section 3.1 presume that the 

time between exposure and diagnosis of cancer exceeds the minimum latency period for each 

cancer type. The minimum latency period is the elapsed time between exposure to a hazardous 

agent and the earliest occurrence of detectable disease caused by that agent. In IREP, the effect 

of the minimum latency period on cancer risks due to radiation exposure is assumed to be 

represented by an S-shaped (sigmoid) function of time that increases from 0 shortly after 

exposure to 1 at a time when latency no longer has an effect on estimated risks (Land et al. 2003; 

NIOSH 2002).12 The value of this function is 0.5 at the midpoint between the two times. Thus, 

the effect of the minimum latency period is to rapidly decrease estimates of cancer risk as the 

time since exposure decreases below times at which the S-shaped function has values near 1. 

 11Although CLL is not considered to be a radiogenic cancer in IREP, VA estimates PC in cases of 

CLL by assuming that CLL is a form of non-Hodgkin’s lymphoma and uses the risk model for lymphoma 

and multiple myeloma in Group 2 (N. Otchin, Department of Veterans Affairs, personal communication; 

April 18, 2006). 

12The assumption of an S-shaped function takes into account that the minimum time required for 

radiation exposure to result in an increase in cancer risk is difficult to estimate, and it avoids an 

assumption of an abrupt increase in risk at some time after exposure. 
 16

 One of three parameterizations of the S-shaped function is assumed to represent the effect 

of latency on risk, depending on the cancer type (Land et al. 2003). For all solid tumors except 

thyroid and bone cancer, the minimum and maximum values of 0 and 1 in the S-shaped function 

are essentially attained at times after exposure less than 4 years and greater than 11 years, 

respectively (i.e., the values at 4 and 11 years are 0.01 and 0.99), and the midpoint is at 7.5 years. 

This function is given by the solid curve in Fig. 3-1; it is also used to represent the minimum 

latency period for lymphoma and multiple myeloma. For thyroid and bone cancer, which have a 

shorter minimum latency period than other solid tumors, the minimum and maximum values in 

the S-shaped function are essentially attained at times after exposure less than 2 years and greater 

than 7 years, respectively, and the midpoint is at 4.5 years. For all types of leukemia, which 

have a shorter minimum latency period than all other cancer types, the minimum and maximum 

values in the S-shaped function are essentially attained at times after exposure less than 1 year 

and about 5 years, respectively, and the midpoint is at 2.25 years. 

 To represent uncertainty in the assumed effects of the minimum latency period on cancer 

risks, the midpoint of each S-shaped function described above is represented by a triangular 

probability distribution that has a maximum value at 7.5, 4.5, or 2.25 years and ranges from 5 to 

10 years, 4 to 5.5 years, or 2 to 2.5 years, respectively (Land et al. 2003). The effect of the 

assumed uncertainty in the midpoint of the S-shaped function for all solid cancers except thyroid 

and bone cancer is also shown in Fig. 3-1. For all cancer types, this uncertainty results in 

substantial increases in estimates of ERR and PC at times after exposure less than the midpoints 

of the triangular distributions, compared with estimates obtained by assuming no uncertainty in 

the S-shaped function (Land et al. 2003). Effects of this uncertainty on estimates of ERR and PC 

are less at times after exposure beyond the midpoints of the triangular distributions. 
 17

Table 3-1. Categories of cancer risk models incorporated in IREPa

Category Cancer types Description of risk model 

Group 1 All digestive cancers other than stomach, 

colon, and rectum; stomach (female only); 

liver; breast 

Risk depends on age at exposure, 

attained age, and sex (all digestive 

cancers other than stomach, colon, 

and rectum only). 

Group 2 Oral cavity and pharynx; esophagus; 

stomach (male only); colon; rectum; 

gallbladder; pancreas; lung (including 

trachea and bronchus)b

; respiratory other 

than lung (e.g., nasal cavity, larynx); 

bone; all connective tissue; ovary; all 

male genitalia (including prostate); 

bladder; kidney and other urinary organs 

except bladder; eye; nervous system 

(including brain); endocrine glands other 

than thyroid; other and ill-defined sites; 

lymphoma and multiple myeloma 

Risk depends on age at exposure, 

attained age, and sex, but model 

structure describing dependencies 

on age at exposure and attained 

age is different from model for 

cancer types in Group 1; risk of 

lung cancer also depends on 

smoking history. 

Group 3 Lung (including trachea and bronchus)b; 

all female genitalia except ovary 

Risk is independent of age at 

exposure and attained age; risk of 

lung cancer depends on sex and 

smoking history. 

Group 4 Malignant melanoma and non-melanoma 

skin cancers (basal cell carcinoma and 

others including squamous cell 

carcinoma)c

; thyroid; leukemia (other 

than chronic lymphocytic leukemia, 

CLL), acute myeloid leukemia (AML), 

chronic myeloid leukemia (CML), and 

acute lymphocytic leukemia (ALL); lung 

cancer due to exposure to radon 

Unique risk model for each cancer 

type. 

a

Risk models, excluding model for lung cancer due to exposure to radon, are discussed in 

Section 3.1. All cancers except CLL are considered to be radiogenic in IREP. 

b

Risk model for lung cancer in Group 2 was developed by Land et al. (2003), whereas a different 

model in Group 3 was used originally by NIOSH (2002). Both risk models for lung cancer are 

incorporated in the version of IREP currently used by VA. c

Risks of skin cancers depend on race or ethnicity.
 18

Figure 3-1. S-shaped (sigmoid) function assumed in IREP to represent effect of minimum 

latency period on reducing risks of all solid cancers except thyroid and bone cancer at 

early times since exposure and its uncertainty. 

0.0

0.2

0.4

0.6

0.8

1.0

0 5 10 15

1st %-ile

5th %-ile

50th %-ile

95th %-ile

99th %-ile

L

ate

n

c

y

a

dju

s

mt e

nt

Time since exposure (y)
 19

4. SCREENING DOSES CALCULATED WITH IREP

 This section presents screening doses for different cancer types that were calculated with 

IREP. These screening doses are tabulated and discussed in Section 4.1. In Section 4.2, 

screening doses calculated with IREP are compared with previous screening doses in the 

CIRRPC table (see Table 2-1). Use of tabulated screening doses in cases of exposure to multiple 

radiation types or exposures in more than one year is discussed in Section 4.3. A summary of 

important points about screening doses tabulated in this report is given in Section 4.4. 

4.1 Tabulation and Discussion of Screening Doses

 Screening doses for different cancer types that were calculated with IREP are given in 

Tables 4-1 through 4-34.13 Screening doses were calculated for selected ages at exposure and 

times since exposure when cancer is diagnosed. The latter quantity is given by the difference 

between the age at diagnosis and age at exposure. Screening doses were estimated by iteration 

using constant equivalent doses, with no uncertainty, as input to IREP. For reasons discussed in 

Section 4.1.2, all screening doses are given to two significant figures. 

 Sections 4.1.1 and 4.1.2 discuss assumptions used in calculating screening doses and the 

accuracy of the results. Section 4.1.3 then discusses screening doses for specific cancer types. 

4.1.1 Calculation of Screening Doses

 With one exception, screening doses in Tables 4-1 through 4-34 were calculated with 

versions of IREP that were developed by NIOSH (2002);13

 versions developed by NIOSH have 

been used by VA in evaluating causation of cancers in veterans who were exposed to ionizing 

radiation. Screening doses for lung cancer in Table 4-11 were calculated with a version of IREP 

 13Most calculations were performed using Version 5.4 of NIOSH-IREP. Screening doses for 

thyroid and bone cancer were calculated using Version 5.5, which incorporated recent changes in models 

used to estimate ERRs for those cancer types. 
 20

that was developed by NIH (Land et al. 2003).14

 As discussed in Section 3.1.4, the current 

version of NIOSH-IREP incorporates both risk models for lung cancer. 

 IREP calculates probability distributions of PC by repeated random sampling of 

probability distributions that represent uncertainties in all parameters and propagation of the 

randomly selected parameter values through the models used to estimate ERR and PC.15

 

Probability distributions of PC generated in IREP include an upper 99% credibility limit, which 

is used to estimate the screening dose in each case. All screening doses were calculated using 

2000 iterations per run, and the random seed to initiate the sampling process was set to 99. 

These are the default settings in NIOSH-IREP and are generally used by VA. 

 All calculations of screening doses assumed acute exposure to high-energy (> 250 keV) 

photons or, in cases of skin cancer, acute exposure to higher-energy (>15 keV) electrons; the 

latter assumption gives the same PC as an assumption of acute exposure to high-energy 

photons.16

 An assumption of acute exposure to photons or electrons results in a higher estimate 

of PC than an assumption of chronic exposure,17

 due to the influence of a dose and dose-rate 

 14Calculations were performed using Version 5.3 of NIH-IREP. 

15The technique of random sampling used in IREP is a form of Monte Carlo sampling referred to 

as midpoint Latin hypercube sampling. In this method, probability distributions of model parameters are 

divided into N intervals of equal probability, where N is the number of iterations per run, and values at 

the midpoints of each of the N intervals are selected in random order. Use of Latin hypercube sampling 

assures that the entire range of probability distributions of all parameters is sampled. This technique thus 

gives a more robust probability distribution of PC for a given number of iterations, especially at an upper 

credibility limit, than conventional Monte Carlo sampling in which parameter values are selected at 

random in each iteration without regard for previously sampled values. 

16It is intended that doses will be entered into IREP by radiation type. Equivalent doses for the 

following radiation types can be entered: photons of energy < 30 keV, 30-250 keV, and > 250 keV; 

electrons of energy < 15 keV and > 15 keV; neutrons of energy < 10 keV, 10-100 keV, 0.1-2 MeV 

(including spectra of fission neutrons), 2-20 MeV, and > 20 MeV; and alpha particles of any energy 

emitted in radioactive decay (Land et al. 2003). When equivalent doses are entered by radiation type, the 

biological effectiveness of each radiation type relative to reference high-energy (> 250 keV) photons and 

its uncertainty are taken into account in calculating probability distributions of PC. 

17To follow guidance by NIOSH (2002), VA assumes that all external exposures to photons or 

electrons are acute, because that assumption is more favorable to claimants than an assumption of chronic 

exposure (N. Otchin, Department of Veterans Affairs, personal communication; April 26, 2006).
 21

effectiveness factor (DDREF) in reducing risks from chronic exposure to those radiation types 

(Land et al. 2003).18

 Use of screening doses in cases of exposure to other radiation types is 

discussed in Section 4.3.1. 

 Screening doses for ages at exposure or times since exposure when cancer was diagnosed 

that are not included in the tables can be estimated by interpolation. Two-dimensional linear 

interpolation should be adequate when screening doses are not changing rapidly. In the tables of 

screening doses, this condition is met when the time since exposure is more than 3 years for all 

types of leukemia, 5 years for thyroid and bone cancer, and 10 years for all other cancer types. 

Of course, the more precise option of running IREP for specific cases is always available. This 

option is recommended when the time since exposure is sufficiently short that the minimum 

latency period has an effect on reducing estimates of ERR and increasing screening doses. 

 Except for cancers of the female breast, ovary, and all female genitalia except ovary, 

tabulated screening doses apply to males only. For cancer types in Groups 1, 2, or 3 that occur in 

males and females and for chronic myeloid leukemia (CML) in Group 4 (see Table 3-1), ERRs 

are assumed to depend on sex, and screening doses for females differ from values for males.19

4.1.2 Accuracy of Calculated Screening Doses

 As noted previously, all screening doses in Tables 4-1 through 4-34 are presented to two 

significant figures only. More specifically, each screening dose is the lowest equivalent dose to 

two significant figures at which the calculated upper 99% credibility limit of PC is 50% or 

greater. Thus, a screening dose is not necessarily the equivalent dose at which the calculated 

 18Probability distributions of DDREF with mean values greater than 1.0 are used in IREP to 

estimate ERRs for all cancer types, except leukemia, from chronic exposure to photons or electrons. For 

acute exposure to those radiation types, DDREF is phased in as the dose decreases below an uncertain 

reference dose between 3 and 20 rem and approaches the assumed DDREF for chronic exposure as the 

dose decreases toward zero (Land et al. 2003). A DDREF also is implicit in the assumed linear-quadratic 

dose-response relationship for leukemia under conditions of acute exposure to photons or electrons. 

19Screening doses for males and females may differ even when ERRs in Japanese atomic-bomb 

survivors are independent of sex, because baseline risks used in modeling the transfer of ERRs to the U.S. 

population may be sex-specific (Land et al. 2003). 
 22

upper 99% credibility limit of PC is closest to 50%.20

 By using this approach, an equivalent 

dose (to two significant figures) less than an applicable screening dose corresponds to a 

calculated upper 99% credibility limit of PC less than 50% when the default settings of 2000 

iterations per run and a random seed of 99 are used. 

 Reporting of screening doses to no more than two significant figures can be justified by 

considering the accuracy of the calculations. If the number of iterations per run is fixed at the 

default setting of 2000, a change in the random seed can have a substantial effect on the 

calculated upper 99% credibility limit of PC. This effect is illustrated by calculations we 

performed with Version 5.5 of NIOSH-IREP, in which an equivalent dose that gave an upper 

99% credibility limit of PC close to 50% for particular combinations of cancer type, age at 

exposure, and attained age were assumed; some of these combinations were selected with the 

intent of maximizing the effect of a change in the random seed.21

 By performing calculations at 

the same equivalent dose but using up to 50 different random seeds, the maximum variation in 

 20If, for example, an equivalent dose (to two significant figures) of 110 rem gives an upper 99% 

credibility limit of PC of 49.96% and an equivalent dose of 120 rem gives a value of 51.23%, the 

tabulated screening dose would be 120 rem. 

21Calculations were performed for the following combinations of cancer type, age at exposure 

(ae), and age at diagnosis of cancer (ad): (1) liver cancer, ae = 18 and ad = 28; (2) cancers of the 

respiratory tract other than lung cancer, ae = 18 and ad = 28; (3) non-melanoma basal cell carcinoma 

(white, non-Hispanics), ae = 18 and ad = 70; (4) basal cell carcinoma (white, non-Hispanics), ae = 40 and 

ad = 70; (5) cancers of all male genitalia (including prostate), ae = 20 and ad = 70; (6) thyroid cancer, 

ae = 18 and ad = 60; and (7) all leukemia excluding CLL, ae = 18 and ad = 70. The first two calculations 

apply to the cancer types in Group 1 and Group 2 (see Section 3.1 and Table 3-1) for which uncertainties 

in the estimated ERR per unit equivalent dose are the highest (Land et al. 2003) and, thus, calculated 

upper 99% credibility limits of PC at a fixed dose are among the most sensitive to changes in the random 

seed. The age at exposure and age at diagnosis in those two calculations were chosen to maximize the 

effect of changes in the random seed. Calculations for basal cell carcinoma and prostate cancer were 

included because these are the most common types of nonpresumptive cancers in VA radiation claims of 

concern to this report. The ages at exposure and ages at diagnosis in the calculations for those two cancer 

types were selected to represent a variety of likely combinations and, in the first calculations for basal cell 

carcinoma, to maximize the effect of changes in the random seed. Calculations for thyroid cancer and 

leukemia were included to investigate the effect for cancer types other than skin cancer with unique risk 

models (see Section 3.1.5). In all calculations, the equivalent dose was fixed at the applicable screening 

dose given in Table 4-7, 4-12, 4-16, 4-22, 4-27, or 4-31. 
 23

the upper 99% credibility limit of PC about the nominal value of 50% was ±3.0 percentage 

points, or ±6.0% of the nominal value of 50%.22,23

 For the purpose of estimating screening doses, we are interested in the variation in the 

dose that gives a calculated upper 99% credibility limit of PC of 50% due to a change in the 

random seed in IREP, rather than the variation in an upper 99% credibility limit of PC of about 

50% at a fixed dose. Since PC is a nonlinear function of dose (see Section 2.1), the two 

variations are not the same. Our analysis of the variation of interest is described as follows. 

 We define the variation in PC due to a change in the random seed as Δ(PC)/PC and the 

corresponding variation in dose as ΔD/D. When ERR is a linear function of dose, as in all risk 

models incorporated in IREP except the model for all types of leukemia under conditions of 

acute exposure to photons and electrons (Land et al. 2003), PC is estimated using eq. (5). By 

differentiating eq. (5) with respect to dose and taking into account that α × D = 1 at a PC of 50%, 

we find that when PC is about 50%, a variation in PC of x at a fixed dose corresponds to a 

variation in dose of 2x at a fixed PC of 50%. This result means that a screening dose is twice as 

sensitive to a change in the random seed as the upper 99% credibility limit of PC of about 50% at 

a fixed dose.24

 Thus, in the example calculations discussed above, in which the maximum 

variation in the upper 99% credibility limit of PC was ±6.0% of the nominal value of 50% at a 

fixed dose, the corresponding variation in the equivalent dose that gives an upper 99% credibility 

 22The maximum variation was obtained in the calculations for liver cancer. In all calculations for 

basal cell carcinoma and prostate cancer, the variation in PC was no more than about ±2.2 percentage 

points, or ±4.4% of the nominal value of 50%. 

23The variation in the upper 99% credibility limit of PC at a fixed dose due to a change in the 

random seed is reduced by increasing the number of iterations per run. When the number of iterations per 

run was increased to 10,000, which is the maximum normally allowed in IREP, the maximum variation in 

the upper 99% credibility limit of PC was about ±1 percentage point, or about ±2% of the nominal value 

of 50%. We used 2000 iterations per run in all calculations to conform to the default used by VA.

24When ERR is assumed to be a linear-quadratic function of dose, as in the risk models 

incorporated in IREP for various types of leukemia under conditions of acute exposure to photons and 

electrons (Land et al. 2003), the same method can be used to show that a screening dose is less than twice 

as sensitive to a change in the random seed as an upper 99% credibility limit of PC of about 50% at a 

fixed dose. Thus, a linear dose-response relationship provides the bounding case for the sensitivity of a 

screening dose to a change in the random seed. 
 24

limit of PC of 50% (i.e., the maximum variation in the screening dose) is ±12%. This result 

applies to the cancer type, age at exposure, and age at time of diagnosis for which the effect is 

expected to be the greatest. The maximum variation in a screening dose due to a change in the 

random seed is less for other cancer types, ages at exposure, and ages at diagnosis.25

 The choice of a random seed to be used as a default in IREP is arbitrary. Therefore, 

results of the analysis described above indicate that reporting of screening doses calculated with 

IREP to more than two significant figures when the default number of iterations per run and 

random seed are used would imply an accuracy in the calculations that is unwarranted. 

 An important implication of the analysis described above is that screening doses 

tabulated in this report should be interpreted with caution. Although the tabulated screening 

doses are intended to correspond to an upper 99% credibility limit of PC of 50%, this 

correspondence clearly is not exact. Thus, it is not necessarily the case that an estimated 

equivalent dose (to two significant figures) equal to or greater than a screening dose tabulated in 

this report corresponds to an actual upper 99% credibility limit of PC of 50% or greater, nor is it 

necessarily the case that an estimated equivalent dose less than a screening dose corresponds to 

an actual upper 99% credibility limit of PC less than 50%.26

 Results of our analysis of the sensitivity of screening doses to the choice of a random 

seed also indicate the extent to which a screening dose tabulated in this report could differ from 

the equivalent dose that corresponds to an actual upper 99% credibility limit of PC of 50%. As 

 25The maximum variation in a calculated upper 99% credibility limit of PC due to a change in the 

random seed in IREP can be much higher than obtained in our analysis if the equivalent dose is assumed 

to be uncertain, rather than fixed at a single value. For example, in a calculation in which the uncertainty 

in an estimated dose was represented by a geometric standard deviation (GSD) of 3 and the median dose 

was set at a value that gave an upper 99% credibility limit of PC close to 50%, the maximum variation in 

the upper 99% credibility limit of PC due to changes in the random seed was nearly ±10% of the nominal 

value of 50% (B.A. Thomas, SENES Oak Ridge, Inc., personal communication; March 9, 2006). An 

assumption of a fixed dose is appropriate for our analysis when VA uses point estimates of equivalent 

dose in evaluating causation of cancer (see Section 2.3, footnote 6). 

26An actual upper 99% credibility limit of PC would only be obtained by specifying a very large 

(essentially infinite) number of iterations per run. When the number of iterations is very large, the choice 

of a random seed no longer has an effect on the calculated probability distribution of PC, essentially 

because nearly all possible combinations of parameter values are selected by random sampling. 
 25

derived above, the largest difference between a calculated screening dose and its actual value 

should be no more than ±12%. Furthermore, the greatest effect of a change in the random seed 

was obtained in the calculations for liver cancer that assumed a very young age at the time of 

diagnosis of cancer (see footnote 21). Such a young age at diagnosis should rarely, if ever, occur 

in VA radiation claims of concern to this report. For more common ages at diagnosis, the 

difference between a calculated screening dose and the equivalent dose that corresponds to an 

actual upper 99% credibility limit of PC of 50% should be less than ±10%.27

4.1.3 Discussion of Screening Doses

 Screening doses in Tables 4-1 through 4-34 show certain dependencies on age at 

exposure and time since exposure when cancer was diagnosed (i.e., difference between age at 

diagnosis and age at exposure). The following discussion of these dependencies assumes that the 

time since exposure when cancer was diagnosed is sufficiently long that assumptions about the 

minimum latency period described in Section 3.2 do not have a significant effect on estimates of 

ERR and PC. When the time since exposure is short (e.g., less than the midpoint of the S-shaped 

function that is assumed to represent the effect of the minimum latency period on risk), screening 

doses increase rapidly with decreasing time since exposure. 

 For all cancer types in Groups 1 and 2 (see Table 3-1), which are the majority of cancer 

types considered in IREP, screening doses increase with increasing age at exposure and time 

since exposure when cancer was diagnosed until a plateau region is reached, where screening 

doses are constant. These dependencies are the result of assumptions about the dependence of 

ERRs on age at exposure and attained age, as described in Section 3.1. In most such cases, the 

minimum screening dose for any age at exposure occurs at a time since exposure when cancer 

 27When more common ages at diagnosis that apply to recent or future VA radiation claims are 

considered (e.g., an age at diagnosis of at least 50), additional calculations indicated that the largest 

difference between a screening dose tabulated in this report and the equivalent dose that corresponds to an 

actual upper 99% credibility limit of PC of 50% is greatly reduced for cancer types in Groups 1 and 2 (see 

Section 3.1 and Table 3-1), including liver cancer. The calculation that gives the largest difference then 

becomes basal cell carcinoma for an age at exposure of 18, and the maximum difference between a 

screening dose and its actual value for that cancer type should not exceed about ±9%. 
 26

was diagnosed of about 10 years or less, depending on the assumption about the effect of the 

minimum latency period on risk (see Section 3.2). Further discussion of screening doses for 

selected cancer types is provided in the following paragraphs. 

 Lung cancer. Screening doses for lung cancer in Tables 4-10 and 4-11 were calculated 

using different risk models (see Section 3.1.4). For younger ages at exposure and earlier times 

since exposure when cancer was diagnosed, screening doses in Table 4-11 often are substantially 

lower than the corresponding values in Table 4-10. This difference is explained by the 

following: screening doses in Table 4-10 were calculated on the basis of an estimate of the 

average ERR associated with radiation exposure in a population of all ages, and that ERR is 

substantially lower than estimated ERRs for younger ages at exposure and earlier attained ages 

that were used in calculating screening doses at those ages in Table 4-11. For never-smokers, 

however, screening doses in Table 4-11 are substantially higher than the corresponding screening 

doses in Table 4-10 for ages at exposure beyond about 25 and times since exposure beyond about 

15 years. At those ages and times, age-specific ERRs used to calculate screening doses for 

never-smokers in Table 4-11 are lower than the average ERR for never-smokers in a population 

of all ages. 

 Skin cancer. Skin cancers are the only cancer types for which risks due to radiation 

exposure are assumed to depend on race or ethnicity. Screening doses for basal cell carcinoma 

(Table 4-16) and squamous cell carcinoma (Table 4-17) are about a factor of 2 higher in white, 

non-hispanics than in blacks. For malignant melanoma, however, screening doses (Table 4-15) 

are less dependent on race or ethnicity. 

 Breast cancer. Screening doses for breast cancer in males (Table 4-19) are slightly lower 

than the corresponding values for females (Table 4-18). Even though the risk model for breast 

cancer is the same for both sexes, there are differences in uncertainties in baseline risks in the 

two sexes that affect upper 99% credibility limits of PC for an individual in the U.S. population. 

 Thyroid cancer. Screening doses for thyroid cancer (Table 4-27) increase more slowly 

with increasing age at exposure than screening doses for other solid tumors. In this case, an 

increase in uncertainty in ERR with increasing age at exposure (Land et al. 2003) has a 

substantial effect on upper 99% credibility limits of PC. In addition, screening doses are 
 27

constant for ages at exposure beyond 50, even though ERR for thyroid cancer is expected to 

decrease with increasing age at exposure beyond age 50. However, the number of thyroid 

cancers in this age group in Japanese atomic-bomb survivors was judged to be too small to 

establish a dependence of ERR on age at exposure, and ERR for thyroid cancer is assumed to be 

independent of age at exposure beyond age 50 (Land et al. 2003). 

 Leukemia. A noteworthy characteristic of screening doses for all leukemia excluding 

CLL (Table 4-31) is that values in the lower-right portion of the table decrease with increasing 

age at exposure and time since exposure when cancer was diagnosed. This behavior is seen even 

though ERR associated with radiation exposure is assumed to decrease exponentially with 

increasing age at exposure to age 55 and time since exposure to 50 years. In the portion of 

Table 4-31 where this behavior is seen, the uncertainty in the estimated ERR is increasing more 

rapidly with increasing age at exposure and time since exposure than the corresponding decrease 

in the central estimate of ERR (Land et al. 2003), resulting in increases in upper 99% credibility 

limits of PC. 

 Screening doses for acute lymphocytic leukemia (ALL) (Table 4-33) show a pronounced 

increase as the age at exposure increases from 18 to 20, provided the time since exposure when 

cancer was diagnosed is about 20 years or less. Those large increases do not result from an 

assumption that the ERR for ALL associated with radiation exposure decreases greatly when the 

age at exposure increases by only 2 years. Rather, screening doses for an age at exposure of 18 

were calculated on the basis of an average ERR for all ages at exposure up to age 20, and that 

ERR is determined primarily by the high ERRs in infants and children when ERR is assumed to 

decrease exponentially with increasing age at exposure. 

4.2 Comparison with Screening Doses in CIRRPC Table

 For cancer types included in the CIRRPC table (Table 2-1), the corresponding screening 

doses calculated with IREP usually are higher. Those increases are due in part to reductions in 

uncertainties in estimated ERRs in exposed populations, mainly Japanese atomic-bomb 

survivors, as the number of cancers on those populations has increased over time. A decrease in 
 28

uncertainty in an estimated ERR results in a decrease in uncertainty in PC and, therefore, an 

increase in the equivalent dose corresponding to an upper 99% credibility limit of PC. 

 In a few cases, a lower screening dose was calculated with IREP compared with the 

corresponding screening dose obtained from the CIRRPC table. These cases include: colon 

cancer and breast cancer for ages at exposure of about 20 years or less and times since exposure 

when cancer was diagnosed of about 10-15 years, and acute lymphocytic leukemia (ALL) for 

ages at exposure less than 20 years and times since exposure less than about 10 years. In those 

cases, changes in data and assumptions used to estimate ERRs other than reductions in 

uncertainties in estimated ERRs in Japanese atomic-bomb survivors are important. Depending 

on the cancer type, important changes may include: (a) increases in central estimates of ERR, 

(b) differences in assumptions about the transfer of ERRs in atomic-bomb survivors to the U.S. 

population to account for differences in baseline risks in the two populations, and (c) a change 

from a linear-quadratic dose-response relationship, as used to calculate screening doses for most 

cancers in the CIRRPC table, to a linear relationship and a DDREF at low doses and low dose 

rates in IREP (Land et al. 2003; NIH 1985). However, a change in the dose-response 

relationship is not relevant for breast cancer, since a linear relationship was assumed previously. 

Furthermore, a change from a linear-quadratic relationship to a linear relationship with a DDREF 

for solid tumors does not apply to any type of leukemia (excluding CLL), since a linear-quadratic 

dose-response relationship for those cancer types was assumed previously and is assumed in 

IREP under conditions of acute exposure to low-LET radiations. 

 Although screening doses calculated with IREP are higher in most cases than the 

corresponding screening doses obtained from the CIRRPC table, increases in screening doses 

should affect compensation decisions in only a small fraction of VA claims. All cancers 

included in the CIRRPC table are presumptive diseases in VA regulations [38 CFR 3.309(d)(2)]. 

Therefore, except as noted in Section 1 (see footnote 2), adjudication of claims for compensation 

for those cancers does not require an evaluation of causation. Screening doses for the most 

common cancers in VA radiation claims (basal cell carcinoma and prostate cancer) are not 

included in the CIRRPC table. However, the lowest screening doses for basal cell carcinoma 
 29

calculated with IREP (Table 4-16) are similar to or less than the screening dose of about 9 rem 

used previously by VA (see Section 2.2). 

 Another difference between screening doses calculated with IREP and screening doses in 

the CIRRPC table concerns their dependence on time since exposure when cancer was 

diagnosed. Screening doses for many cancer types calculated with IREP increase with 

increasing time since exposure when that time is sufficiently long that an assumption about the 

minimum latency period (see Section 3.2) does not have a significant effect on estimated ERRs. 

However, with the exception of the various types of leukemia, screening doses in the CIRRPC 

table are independent of time since exposure when cancer was diagnosed. 

4.3 Application of Screening Doses

 Comparisons of estimated equivalent doses to individuals with screening doses tabulated 

in this report may be straightforward in some cases. However, additional consideration needs to 

be given to cases in which an individual was exposed to multiple radiation types or exposures 

occurred in more than one year. These situations are discussed in the following sections. 

4.3.1 Exposure to Multiple Radiation Types

 Screening doses in Tables 4-1 through 4-34 are equivalent doses to organs or tissues in 

which each cancer type occurs. Therefore, the dose to an individual that should be compared 

with a screening dose is a total equivalent dose from all radiation types combined that takes into 

account the biological effectiveness of different radiation types. Alpha particles and neutrons are 

the high-LET radiations of concern for which the biological effectiveness is considerably greater 

than for high-energy photons. 

 As noted in Section 1, estimates of equivalent dose that are provided by DTRA for use by 

VA in adjudicating claims are intended to be at least upper 95% credibility limits of uncertain 

doses. Therefore, upper credibility limits of total equivalent doses to be compared with tabulated 

screening doses should take into account uncertainties in the biological effectiveness of alpha 
 30

particles and neutrons when exposure to those radiation types occurred, as well as uncertainties 

in absorbed doses.28

 Uncertainties in the biological effectiveness of alpha particles and neutrons 

that can be used in estimating upper bounds of equivalent dose from these radiation types are 

represented by probability distributions of radiation effectiveness factors (REFs) that were 

developed by Kocher et al. (2002; 2005) for use in IREP (Land et al. 2003).29,30

 Uncertainties in 

the biological effectiveness of alpha particles and neutrons should also take into account a small 

correction to probability distributions of REFs to represent an assumed inverse dose-rate effect 

and its uncertainty.31

 28These considerations also apply to the use of screening doses in the CIRRPC table (Table 2-1). 

29It is important to emphasize that uncertainties in the biological effectiveness of alpha particles 

and neutrons should not be taken into account when estimating equivalent doses from those radiation 

types to be used as input to IREP. Since uncertainties in REFs are incorporated in IREP, they are taken 

into account when IREP is used to calculated an upper 99% credibility limit of PC. Therefore, when 

IREP is used, equivalent doses from alpha particles and neutrons (including upper bounds used by VA in 

adjudicating claims for compensation) should be estimated using point values of radiation weighting 

factors (wR) recommended by ICRP (1991), without uncertainty; the recommended wR is 20 for alpha 

particles and fission neutrons. The need to account for uncertainty in the biological effectiveness of alpha 

particles and neutrons in estimating equivalent doses arises only when an estimated upper bound of the 

total equivalent dose from all radiation types combined is compared with a tabulated screening dose. 

30Caution is advised when estimated total equivalent doses to be compared with tabulated 

screening doses for various types of leukemia include significant contributions from alpha particles or 

neutrons. Such comparisons are difficult when the dose-response relationship for acute exposure to 

photons assumed in calculating screening doses is linear-quadratic, but the dose-response relationship for 

alpha particles and neutrons is linear. This difference is not a concern for cancer types other than 

leukemia. 

31This correction represents an assumption that the biological effectiveness of high-LET 

radiations increases with decreasing dose rate and, thus, that the risk from chronic exposure at a given 

dose is higher than the risk from acute exposure at the same dose. In using IREP, VA assumes that all 

exposures to alpha particles are chronic and, to follow guidance provided by NIOSH (2002), VA uses the 

same assumption for external exposure to neutrons because it is more favorable to claimants. Therefore, 

when using tabulated screening doses in cases of exposure to those radiation types, an inverse dose-rate 

effect should be taken into account in estimating upper bounds of equivalent doses, to be consistent with 

VA’s assumptions. If VA were to change its policy and assume that all exposures of service personnel to 

neutrons at atmospheric nuclear-weapons tests were acute, an REF for neutrons uncorrected for an inverse 

dose-rate effect should be used in estimating upper bounds of equivalent doses. 
 31

4.3.2 Exposures in More Than One Year

 Another complicating factor in using tabulated screening doses arises when exposures 

occurred in more than one year (i.e., at more than one age). Exposures in more than one year can 

affect comparisons of estimated equivalent doses with screening doses when the screening dose 

depends on age at exposure and time since exposure when cancer was diagnosed. This situation 

occurs for most cancer types. As described below, suitable approaches to addressing exposures 

in more than one year depend on whether the intent is to use a screening dose to show that the 

upper 99% credibility limit of PC associated with estimated equivalent doses is clearly less than 

50% or clearly greater than 50%. All suitable approaches discussed below involve comparisons 

of the total equivalent dose from all years of exposure with an applicable screening dose for the 

cancer type of concern. 

 If a screening dose is used to determine whether estimated equivalent doses correspond to 

an upper 99% credibility limit of PC that is clearly less than 50%, the simplest approach to 

accounting for exposures in multiple years is to compare the total equivalent dose with the 

lowest screening dose for the cancer type of concern that applies to any age at exposure and time 

since exposure when cancer was diagnosed. In making such comparisons, it is important to take 

into account the accuracy of screening doses calculated with IREP (i.e., potential differences 

between tabulated screening doses and the equivalent dose that corresponds to an actual upper 

99% credibility limit of PC of 50%), as discussed in Section 4.1.2. The lowest tabulated 

screening dose for each cancer type is given in Table 4-35. If the estimated upper bound (at least 

an upper 95% credibility limit) of the total equivalent dose from exposure in all years is less than 

the lowest screening dose that applies to the cancer type of concern, the upper 99% credibility 

limit of PC is less than 50%. This conclusion applies without regard for the distribution of 

equivalent dose with age at exposure or the age at the time of diagnosis. 

 For all cancer types except leukemia, an alternative approach can be used to demonstrate 

that estimated equivalent doses correspond to an upper 99% credibility limit of PC that is clearly 

less than 50%. In this approach, the total equivalent dose is compared with the screening dose 

(again with due consideration of its accuracy) that applies to the youngest age at exposure and a 
 32

time since exposure given by the difference between the age at diagnosis and the oldest age at 

exposure (age during the year of last exposure). This alternative is valid when screening doses 

do not decrease with increasing age at exposure or time since exposure when cancer was 

diagnosed. However, it should be used only when the difference between the age at diagnosis 

and oldest age at exposure exceeds the time over which the minimum latency period for the 

cancer type of concern has a significant effect on estimated risks. 

 The alternative approach described above also is valid for specific types of leukemia 

(CML, ALL, and AML) in many cases, given the dependence of screening doses (Tables 4-32, 

4-33, and 4-34) on age at exposure and time since exposure when cancer was diagnosed. 

However, as indicated by the dependence of screening doses for all leukemia as a group 

(Table 4-31) on age at exposure and time since exposure when cancer was diagnosed (see 

Section 4.1.3), this alternative may not be valid when using screening doses in that table. For 

example, it may not be valid if significant external doses were received in different years, or if a 

substantial fraction of the total equivalent dose resulted from intakes of long-lived radionuclides 

that are tenaciously retained in the body and deliver a dose over many years. In both examples, 

an assumption that a total equivalent dose was received at the youngest age at exposure could 

result in a substantial underestimate of ERR and PC in some cases. 

 We now consider the use of screening doses to demonstrate that estimated equivalent 

doses correspond to an upper 99% credibility limit of PC that is clearly greater than 50%. One 

of two approaches to comparing the total equivalent dose with a screening dose (again with due 

consideration of its accuracy) can be used.32

 The first approach, which can be used for all cancer 

types, is to use only the highest equivalent dose in any year. This approach is particularly 

 32The approaches described here apply only if acute exposure is assumed, because an assumption 

of acute exposure to photons or electrons was used in calculating all screening doses. If chronic exposure 

were assumed, in which case the full DDREF in IREP would be applied, the estimated PC at a given dose 

would be less and, therefore, the applicable screening dose would be greater than values tabulated in this 

report. As noted previously, VA assumes that all external exposures to photons or electrons are acute in 

using IREP to calculate an upper 99% credibility limit of PC, in order to be more favorable to claimants; 

only internal exposures to those radiation types are assumed to be chronic. The restriction to an 

assumption of acute exposure does not apply when a screening dose is used to demonstrate that estimated 

equivalent doses correspond to an upper 99% credibility limit of PC that is clearly less than 50%. 
 33

appropriate when the total dose is dominated by the dose in a single year. If the highest 

equivalent dose in any year equals or exceeds the screening dose for that age at exposure and 

time since exposure when cancer was diagnosed, the upper 99% credibility limit of PC would 

clearly be greater than 50%. The second approach is to compare the total equivalent dose with 

the screening dose that applies to the oldest age at exposure and a time since exposure given by 

the difference between the age at diagnosis and the youngest age at exposure (age during the year 

of first exposure). This approach is valid except when using screening doses for all leukemia as 

a group (Table 4-31) or ALL (Table 4-33) for some ages at exposure and times since exposure. 

4.4 Summary Discussion of Calculated Screening Doses

 In considering and using screening doses tabulated in this report, certain assumptions 

embodied in the calculations with IREP and the implications of those assumptions should be 

borne in mind. Important points about screening doses are summarized as follows: 

• All screening doses were calculated using the default number of iterations per run (2000) 

and random seed (99) in IREP; these defaults are assumed by VA when IREP is used to 

calculate an upper 99% credibility limit of PC for the purpose of evaluating causation of 

cancer in veterans who were exposed to ionizing radiation. Since calculated screening 

doses can vary substantially with changes in the number of iterations per run and the 

random seed, screening doses should not be interpreted as giving equivalent doses that 

correspond to an upper 99% credibility limit of PC of exactly 50% (see Section 4.1.2). 

• All screening doses were calculated by assuming acute exposure to high-energy photons 

(> 250 keV) or higher-energy electrons (> 15 keV) to be consistent with assumptions 

used by VA in using IREP to calculate an upper 99% credibility limit of PC in cases of 

external exposure to those radiation types. Screening doses that would be obtained by 

assuming chronic exposure to those radiation types are higher (see Section 4.1.1.). 

• Screening doses can be used when exposure to alpha particles or neutrons occurred. 

However, uncertainties in the biological effectiveness of those radiations (including an 
 34

inverse dose-rate effect) need to be taken into account when an estimated equivalent dose 

to be used in comparisons with a screening dose is intended to be an upper bound (at least 

an upper 95% credibility limit). Caution is also advised in using screening doses for 

various types of leukemia when doses from alpha particles or neutrons are a significant 

contributor to the total equivalent dose (see Section 4.3.1). 

• All screening doses are presented to two significant figures. This is an important 

consideration when a screening dose is 100 rem or greater. Each screening dose is the 

lowest equivalent dose (to two significant figures) at which the calculated upper 99% 

credibility limit of PC is 50% or greater; a screening dose is not necessarily the 

equivalent dose that gives a calculated upper 99% credibility limit of PC closest to 50%. 

• On the basis of an analysis of the variation in calculated screening doses due only to a 

change in the random seed in IREP when the number of iterations per run is fixed at the 

default value (see Section 4.1.2), the equivalent dose that corresponds to an actual upper 

99% credibility limit of PC of 50% could differ from a screening dose tabulated in this 

report by no more than ±12% in the worst case. This difference should be less than 

±10% in almost all cases of practical interest in VA radiation claims. 

 Screening doses tabulated in this report are potentially useful in several ways. When due 

consideration is given to their accuracy, screening doses can be used to indicate whether the 

upper 99% credibility limit of PC associated with estimated equivalent doses is clearly less than 

50% or clearly greater than 50%. Thus, for example, they can be used to provide a check of the 

validity of calculated upper 99% credibility limits of PC and the resulting decision on granting a 

claim for compensation for cancer in specific cases. More generally, we believe that the most 

important use of screening doses is to give a general indication of the magnitude of radiation 

doses that are required to warrant a favorable compensation decision. 
 35

Table 4-1. Screening doses (rem) calculated with IREP: 

Cancers of oral cavity and pharynx (including lip)a,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 110 32 45 61 77 93 (98)d

20 160 43 59 76 95 120 

25 300 82 110 140 160 160 

30 530 150 170 210 210 210 

35 740 190 210 210 210 210 

≥ 40 890 210 210 210 210 210 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 36

Table 4-2. Screening doses (rem) calculated with IREP: 

Cancer of esophagusa,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 41 12 16 22 28 33 (35)d

20 56 15 21 28 34 40 

25 120 28 37 47 56 56 

30 210 50 61 72 72 72 

35 270 64 72 72 72 72 

≥ 40 340 77 72 72 72 72 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 37

Table 4-3. Screening doses (rem) calculated with IREP: 

Cancer of stomacha,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 40 9.0 13 17 22 26 (27)d

20 54 12 16 21 27 32 

25 110 22 29 37 44 44 

30 210 40 48 58 58 58 

35 270 50 58 58 58 58 

≥ 40 330 61 58 58 58 58 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 38

Table 4-4. Screening doses (rem) calculated with IREP: 

Cancer of colona,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 40 12 17 24 31 37 (39)d

20 54 16 23 31 38 45 

25 110 33 41 54 64 64 

30 210 57 70 85 85 85 

35 280 74 85 85 85 85 

≥ 40 330 89 85 85 85 85 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 39

Table 4-5. Screening doses (rem) calculated with IREP: 

Cancer of rectum (including anus and anal canal)a,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 150 36 50 66 83 100 (110)d

20 190 48 63 83 110 130 

25 370 91 120 150 180 180 

30 650 160 200 230 230 230 

35 880 210 230 230 230 230 

≥ 40 1100 240 230 230 230 230 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 40

Table 4-6. Screening doses (rem) calculated with IREP: 

Cancers of digestive tract other than stomach, colon, and rectuma,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 76 22 30 42 53 63 (66)d

20 110 28 38 51 64 75 

25 190 49 63 81 96 96 

30 310 79 96 120 120 120 

35 410 110 120 120 120 120 

≥ 40 510 130 120 120 120 120 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). Specific organs 

and tissues to which this cancer type applies are listed in Table 4 of NIOSH (2002), and the risk model for 

this cancer type is described in Section 3.1.1. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 41

Table 4-7. Screening doses (rem) calculated with IREP: 

Cancer of liver (including biliary system)a,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 15 4.0 5.3 7.3 8.8 11 (11)d

20 19 5.2 6.7 8.5 11 13 

25 35 8.5 11 14 16 16 

30 60 14 17 20 20 20 

35 78 18 20 20 20 20 

≥ 40 96 22 20 20 20 20 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.1. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 42

Table 4-8. Screening doses (rem) calculated with IREP: 

Cancer of gallbladder (including bile ducts)a,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 24 6.0 7.8 11 13 16 (17)d

20 33 7.6 9.8 13 16 18 

25 68 14 17 21 24 24 

30 130 24 27 33 33 33 

35 160 30 33 33 33 33 

≥ 40 190 34 33 33 33 33 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 43

Table 4-9. Screening doses (rem) calculated with IREP: 

Cancer of pancreasa,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 120 31 42 55 70 84 (89)d

20 150 40 53 70 86 110 

25 310 74 93 130 150 150 

30 540 140 160 200 200 200 

35 710 170 200 200 200 200 

≥ 40 900 200 200 200 200 200 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 44

Table 4-10. Screening doses (rem) calculated with IREP: 

Cancer of lung (including trachea and bronchus) – Ia,b

Time since exposure when cancer was diagnosed (y)c

Smoking status Age at exposure 

(y) 5 10 ≥ 15 

Never smoker Any 220 46 44 

Former smoker Any 530 130 130 

Current smokerd

 Any 720 160 150 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Sections 3.1.3 and 3.1.4. c

Difference between age at diagnosis and age at exposure. 

d

Screening doses apply when the number of cigarettes smoked per day is unknown. IREP also 

calculates PC for separate smoking categories of < 10, 10-19, 20-40, and ≥ 40 cigarettes per day; 

screening doses for these smoking categories are similar to values for former smokers and current 

smokers with an unknown number of cigarettes smoked per day. 
 45

Table 4-11. Screening doses (rem) calculated with IREP: 

Cancer of lung (including trachea and bronchus) – IIa,b,c

Time since exposure when cancer was diagnosed (y)d Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 58 

95 

100 

18 

23 

23 

26 

32 

33 

35 

43 

44 

44 

54 

54 

52 (54)e

63 (66) 

64 (68) 

20 76 

120 

140 

24 

30 

31 

33 

41 

42 

44 

54 

54 

55 

65 

67 

63 

76 

78 

25 150 

250 

250 

45 

56 

57 

60 

71 

73 

77 

89 

91 

90 

110 

110 

90 

110 

110 

30 270 

420 

440 

80 

95 

97 

100 

120 

120 

120 

140 

140 

120 

140 

140 

120 

140 

140 

35 360 

550 

570 

100 

120 

120 

120 

140 

140 

120 

140 

140 

120 

140 

140 

120 

140 

140 

≥ 40 450 

680 

720 

130 

150 

150 

120 

140 

140 

120 

140 

140 

120 

140 

140 

120 

140 

140 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.3 of NIH-IREP (Land et al., 2003). The risk model 

for this cancer type is described in Sections 3.1.2 and 3.1.4. c

For each age at exposure and time since exposure when cancer was diagnosed, first entry gives 

the screening dose for never smokers, second entry gives the screening dose for former smokers, and third 

entry gives the screening dose for current smokers that applies when the number of cigarettes smoked per 

day is unknown. IREP also calculates PC for separate smoking categories of < 10, 10-19, 20-40, and 

≥ 40 cigarettes per day; screening doses for these smoking categories are similar to values for former 

smokers and current smokers with an unknown number of cigarettes smoked per day. 

d

Difference between age at diagnosis and age at exposure. 

e

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater).
 46

Table 4-12. Screening doses (rem) calculated with IREP: 

Cancers of respiratory tract other than lunga,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 150 34 47 62 79 94 (100)d

20 210 45 59 78 95 120 

25 360 83 110 130 160 160 

30 630 150 170 210 210 210 

35 840 190 210 210 210 210 

≥ 40 1100 220 210 210 210 210 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). Specific organs 

and tissues to which this cancer type applies are listed in Table 4 of NIOSH (2002), and the risk model for 

this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 47

Table 4-13. Screening doses (rem) calculated with IREP: 

Cancer of bonea,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 3 5 10 15 20 25 ≥ 30 

18 33 10 14 21 30 38 45 (48)d

20 47 14 19 28 37 47 55 

25 96 32 37 51 64 76 76 

30 190 61 66 84 110 110 110 

35 270 83 84 110 110 110 110 

≥ 40 320 110 110 110 110 110 110 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.5 of NIOSH-IREP (NIOSH, 2002); see 

Section 4.1.1, footnote 13. The risk model for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 48

Table 4-14. Screening doses (rem) calculated with IREP: 

Cancers of connective tissue (including other soft tissue not listed)a,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 48 16 23 31 39 47 (50)d

20 69 21 29 39 49 58 

25 140 41 53 67 80 80 

30 260 72 87 110 110 110 

35 330 92 110 110 110 110 

≥ 40 410 120 110 110 110 110 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer types occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater).
 49

Table 4-15. Screening doses (rem) calculated with IREP: 

Malignant melanoma of skina,b

Time since exposure when cancer was diagnosed (y)c

White, non-hispanicd Black Age at d

exposure (y) 

5 10 ≥ 15 5 10 ≥ 15 

18 35 6.3 5.9 28 5.6 5.3 

20 49 8.4 7.9 37 7.7 7.3 

25 94 17 16 72 15 15 

30 190 33 31 140 30 29 

35 310 55 51 250 49 47 

≥ 40 550 91 86 440 80 77 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.5. c

Difference between age at diagnosis and age at exposure. 

d

 IREP also calculates risks of skin cancers for the following racial or ethnic groups: American 

Indians or Alaska natives; Asians, native Hawaiians, or other Pacific islanders; and white Hispanics. 
 50

Table 4-16. Screening doses (rem) calculated with IREP: 

Basal cell carcinoma of skina,b

Time since exposure when cancer was diagnosed (y)c

White, non-hispanicd Black Age at d

exposure (y) 

5 10 ≥ 15 5 10 ≥ 15 

18 36 6.2 5.9 18 3.2 3.1 

20 48 8.5 7.9 24 4.3 4.0 

25 94 17 16 46 7.9 7.4 

30 190 33 31 89 15 15 

35 320 54 51 160 26 24 

≥ 40 550 89 87 270 44 42 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.5. c

Difference between age at diagnosis and age at exposure. 

d

IREP also calculates risks of skin cancers for the following racial and ethnic groups: American 

Indians or Alaska natives; Asians, native Hawaiians, or other Pacific islanders; and white Hispanics. 
 51

Table 4-17. Screening doses (rem) calculated with IREP: 

Squamous cell carcinoma of skina,b

Time since exposure when cancer was diagnosed (y)c

White, non-hispanicd Black Age at d

exposure (y) 

5 10 ≥ 15 5 10 ≥ 15 

All 2500 310 300 1100 160 150 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.5. c

Difference between age at diagnosis and age at exposure. 

d

IREP also calculates risks of skin cancers for the following racial and ethnic groups: American 

Indians or Alaska natives; Asians, native Hawaiians, or other Pacific islanders; and white Hispanics. 
 52

Table 4-18. Screening doses (rem) calculated with IREP: 

Cancer of breast (female)a,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 49 14 22 33 43 53 (57)d

20 64 18 27 39 51 62 

25 130 32 45 60 75 75 

30 230 51 66 84 84 84 

35 300 69 84 84 84 84 

≥ 40 380 89 84 84 84 84 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.1. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 53

Table 4-19. Screening doses (rem) calculated with IREP: 

Cancer of breast (male)a,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 38 12 20 30 41 50 (53)d

20 51 16 25 37 49 58 

25 94 29 41 56 70 70 

30 160 46 61 78 78 78 

35 210 63 78 78 78 78 

≥ 40 270 80 78 78 78 78 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.1. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater).
 54

Table 4-20. Screening doses (rem) calculated with IREP: 

Cancer of ovarya,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 42 14 19 25 32 38 (41)d

20 60 17 23 32 39 46 

25 120 33 42 53 63 63 

30 220 57 69 82 82 82 

35 290 73 82 82 82 82 

≥ 40 350 87 82 82 82 82 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 55

Table 4-21. Screening doses (rem) calculated with IREP: 

Cancers of all female genitalia other than ovarya,b

Time since exposure when cancer was diagnosed (y)c

Age at exposure (y) 

5 10 ≥ 15 

All 26000 1600 1500 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.3. c

Difference between age at diagnosis and age at exposure. 
 56

Table 4-22. Screening doses (rem) calculated with IREP: 

Cancers of all male genitalia (including prostate)a,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 89 21 28 38 47 56 (60)d

20 120 27 36 47 57 68 

25 250 50 61 77 91 91 

30 420 85 99 120 120 120 

35 490 110 120 120 120 120 

≥ 40 650 130 120 120 120 120 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 57

Table 4-23. Screening doses (rem) calculated with IREP: 

Cancer of bladdera,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 48 16 22 31 38 46 (49)d

20 64 21 29 38 47 56 

25 140 40 51 64 77 77 

30 260 69 84 100 100 100 

35 330 88 100 100 100 100 

≥ 40 400 110 100 100 100 100 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 58

Table 4-24. Screening doses (rem) calculated with IREP: 

Cancers of kidney and other urinary organs except bladdera,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 41 14 21 29 36 44 (46)d

20 57 19 27 36 45 53 

25 120 38 49 63 75 75 

30 220 67 83 100 100 100 

35 290 87 100 100 100 100 

≥ 40 370 110 100 100 100 100 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). Specific organs 

and tissues to which this cancer type applies are listed in Table 4 of NIOSH (2002), and the risk model for 

this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 59

Table 4-25. Screening doses (rem) calculated with IREP: 

Cancer of eyea,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 51 16 23 30 39 47 (49)d

20 71 21 29 39 48 57 

25 150 41 52 67 78 78 

30 270 73 87 110 110 110 

35 360 92 110 110 110 110 

≥ 40 430 120 110 110 110 110 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 60

Table 4-26. Screening doses (rem) calculated with IREP: 

Cancers of nervous system (including brain)a,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 120 32 44 60 74 89 (95)d

20 170 42 57 73 92 110 

25 350 78 100 130 150 150 

30 570 140 160 190 190 190 

35 760 170 190 190 190 190 

≥ 40 960 200 190 190 190 190 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). Specific organs 

and tissues to which this cancer type applies are listed in Table 4 of NIOSH (2002), and the risk model for 

this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 61

Table 4-27. Screening doses (rem) calculated with IREP: 

Cancer of thyroida,b

Time since exposure when cancer was diagnosed (y)c

Age at exposure (y) 

3 5 ≥ 10 

18 44 9.4 7.5 

20 51 11 8.3 

25 71 15 12 

30 110 23 18 

35 160 34 26 

40 180 36 29 

45 220 39 31 

≥ 50 250 43 34 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.5 of NIOSH-IREP (NIOSH, 2002); see 

Section 4.1.1, footnote 13. The risk model for this cancer type is described in Section 3.1.5. c

Difference between age at diagnosis and age at exposure.
 62

Table 4-28. Screening doses (rem) calculated with IREP: 

Cancers of endocrine glands other than thyroida,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 42 14 20 28 36 42 (45)d

20 58 19 27 35 44 51 

25 130 37 47 61 74 74 

30 230 66 81 96 96 96 

35 290 83 96 96 96 96 

≥ 40 360 99 96 96 96 96 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 63

Table 4-29. Screening doses (rem) calculated with IREP: 

Cancers of other and ill-defined sitesa,b

Time since exposure when cancer was diagnosed (y)c Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 52 16 23 31 40 48 (50)d

20 72 21 29 39 49 58 

25 150 42 53 68 81 81 

30 280 74 88 110 110 110 

35 360 93 110 110 110 110 

≥ 40 430 120 110 110 110 110 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). The risk model 

for this cancer type is described in Section 3.1.2. c

Difference between age at diagnosis and age at exposure. 

d

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 64

Table 4-30. Screening doses (rem) calculated with IREP: 

Lymphoma and multiple myelomaa,b,c

Time since exposure when cancer was diagnosed (y)d Age at 

exposure 

(y) 5 10 15 20 25 ≥ 30 

18 96 22 30 38 48 57 (61)e

20 120 29 37 47 59 70 

25 230 50 64 78 93 93 

30 420 88 110 130 130 130 

35 520 110 130 130 130 130 

≥ 40 690 140 130 130 130 130 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). Specific 

diseases to which this cancer type applies are listed in Table 4 of NIOSH (2002), and the risk model for 

this cancer type is described in Section 3.1.2. c

VA assumes that chronic lymphocytic leukemia (CLL) is a form of non-Hodgkin’s lymphoma. 

d

Difference between age at diagnosis and age at exposure. 

e

First entry applies at time since exposure of 30 years; second entry in parentheses applies at time 

since exposure of 32 years or greater (age at diagnosis of 50 years or greater). 
 65

Table 4-31. Screening doses (rem) calculated with IREP: 

All leukemia excluding chronic lymphocytic leukemia (CLL)a,b,c

Time since exposure when cancer was diagnosed (y)d Age at 

exposure 

(y) 3 5 10 15 20 25 30 35 40 45 ≥ 50 

18 2.2 1.9 4.4 9.1 17 28 41 58 78 110 140 

20 2.5 2.2 4.8 9.8 18 29 42 59 79 110 140 

25 3.4 3.0 6.1 12 20 31 44 59 78 100 130 

30 4.5 3.9 7.4 14 22 32 44 57 73 92 120 

35 5.7 5.0 8.8 15 23 32 42 53 65 78 94 

40 6.9 6.0 11 16 24 31 38 46 53 61 69 

45 8.0 7.0 12 17 23 29 34 37 40 43 46 

50 9.2 8.0 12 18 23 26 28 29 29 28 27 

≥ 55 11 8.8 13 19 22 24 23 21 19 17 15 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

The corresponding cancer type in the CIRRPC table (Table 2-1) is leukemia (excluding chronic 

lymphatic). c

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). Specific 

diseases to which this cancer type applies are listed in Table 4 of NIOSH (2002), and the risk model for 

this cancer type is described in Section 3.1.5. 

d

Difference between age at diagnosis and age at exposure. 
 66

Table 4-32. Screening doses (rem) calculated with IREP: 

Chronic myeloid leukemia (CML)a,b,c

Time since exposure when cancer was diagnosed (y)d Age at 

exposure 

(y) 3 5 10 15 20 25 30 35 40 45 50 

All 1.6 1.4 5.0 12 22 37 57 86 130 180 240 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

The corresponding cancer type in the CIRRPC table (Table 2-1) is chronic granulocytic 

leukemia. c

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). Specific 

diseases to which this cancer type applies are listed in Table 4 of NIOSH (2002), and the risk model for 

this cancer type is described in Section 3.1.5. 

d

Difference between age at diagnosis and age at exposure. 
 67

Table 4-33. Screening doses (rem) calculated with IREP: 

Acute lymphocytic leukemia (ALL)a,b,c

Time since exposure when cancer was diagnosed (y)d Age at 

exposure 

(y) 3 5 10 15 20 25 30 35 40 45 50 

18 0.28 0.24 0.91 2.7 6.5 13 24 40 64 110 160 

≥ 20 19 16e

 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Acute leukemia of unspecified type is included in the CIRRPC table (Table 2-1). 

c

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). Specific 

diseases to which this cancer type applies are listed in Table 4 of NIOSH (2002), and the risk model for 

this cancer type is described in Section 3.1.5. 

d

Difference between age at diagnosis and age at exposure. 

e

Entry applies at all times since exposure when cancer was diagnosed of 5 years or greater. 
 68

Table 4-34. Screening doses (rem) calculated with IREP: 

Acute myeloid leukemia (AML)a,b,c

Time since exposure when cancer was diagnosed (y)d Age at 

exposure 

(y) 3 5 10 15 20 25 30 35 40 45 50 

All 6.7 5.8 9.1 14 19 25 29 33 35 38 39 

a

Screening doses are equivalent doses, to two significant figures, to the organ or tissue in which 

cancer type occurs that are intended to correspond to an upper 99% credibility limit of PC of 50%. 

Calculations are described in Section 4.1.1 and the accuracy of screening doses is discussed in 

Section 4.1.2. 

b

Acute leukemia of unspecified type is included in the CIRRPC table (Table 2-1). 

c

Calculations were performed with Version 5.4 of NIOSH-IREP (NIOSH, 2002). Specific 

diseases to which this cancer type applies are listed in Table 4 of NIOSH (2002), and the risk model for 

this cancer type is described in Section 3.1.5. 

d

Difference between age at diagnosis and age at exposure. 
 69

Table 4-35. Lowest screening doses for any age at exposure and time since exposure 

when cancer was diagnosed for all cancer types calculated with IREPa

Cancer type Screening dose 

(rem) Cancer type Screening dose 

(rem) 

Oral cavity and pharynx 

(including lip) 

32 Non-melanoma basal cell 

carcinoma of skin 

3.1 (5.9)c

Esophagus 12 Non-melanoma squamous 

cell carcinoma of skin 

150 (300)c

Stomach 9.0 Breast (female) 14 

Colon 12 Breast (male) 12 

Rectum (including anus 

and anal canal) 

36 Ovary 14 

Digestive tract other than 

stomach, colon, and rectum 

22 All female genitalia other 

than ovary 

1500 

Liver (including biliary 

system) 

4.0 All male genitalia 

(including prostate) 

21 

Gallbladder (including bile 

ducts) 

6.0 Bladder 16 

Pancreas 31 Kidney and other urinary 

organs except bladder 

14 

Lung (including trachea 

and bronchus)b

18 Eye 16 

Respiratory tract other than 

lung 

34 Nervous system (including 

brain) 

32 

Bone 10 Thyroid 7.5 

Connective tissue 

(including other soft tissues 

not listed) 

16 Endocrine glands other 

than thyroid 

14 

Malignant melanoma of 

skin 

5.3 (5.9)c Other and ill-defined sites 16 

 Table is continued on following page. 
 70

Table 4-35. (continued) 

Cancer type Screening dose 

(rem) Cancer type Screening dose 

(rem) 

Lymphoma and multiple 

myeloma 

22 Acute lymphocytic 

leukemia (ALL) 

0.24 

Leukemia excluding 

chronic lymphocytic 

leukemia (CLL) 

1.9 Acute myeloid leukemia 

(AML) 

5.8 

Chronic myeloid leukemia 

(CML) 

1.4 

a

Lowest screening dose for each cancer type is obtained from Tables 4-1 through 4-34. Values 

apply to age at exposure of 18 and shortest time since exposure when cancer was diagnosed at which 

assumption about minimum latency period does not have significant effect on estimated risk (see 

Section 3.2). 

b

Lowest screening dose for never smokers calculated with NIH-IREP (Land et al., 2003) and 

obtained from Table 4-11. Lowest screening dose calculated with NIOSH-IREP (NIOSH, 2002) and 

given in Table 4-12 is higher. c

First entry applies to blacks; second entry in parentheses applies to white, non-Hispanics. 
 71

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(December 17). 
 73

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