Draft

Advisory Board on Radiation and Worker Health

National Institute for Occupational Safety and Health

A Review of ORAUT-OTIB-0087 for Extremity Doses for 

Mound Exposures to Plutonium-238

Contract No. 75D30119C04183

Document No. SCA-TR-2023-PR087, Revision 0

Prepared by

Ron Buchanan, PhD, CHP

Richard Griffiths

SC&A, Inc.

2200 Wilson Blvd., Suite 300

Arlington, VA 22201-3324

April 21, 2023 

DISCLAIMER

This is a working document provided by the Centers for Disease Control and Prevention (CDC) 

technical support contractor, SC&A for use in discussions with the National Institute for 

Occupational Safety and Health (NIOSH) and the Advisory Board on Radiation and Worker 

Health (ABRWH), including its Working Groups or Subcommittees. Documents produced by 

SC&A, such as memorandum, white paper, draft or working documents are not final NIOSH or 

ABRWH products or positions, unless specifically marked as such. This document prepared by 

SC&A represents its preliminary evaluation on technical issues.

NOTICE: This document has been reviewed to identify and redact any information that is 

protected by the Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 
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SC&A, Inc. technical support for the Advisory Board on Radiation and Worker Health’s 

review of NIOSH dose reconstruction program

Document title A Review of ORAUT-OTIB-0087 for Extremity Doses for Mound 

Exposures to Plutonium-238

Document number SCA-TR-2023-PR087

Revision number 0 (Draft)

Supersedes NA

Effective date April 21, 2023

Task manager Kathleen Behling [signature on file]

Project manager Bob Barton, CHP [signature on file]

Document reviewer(s) Bob Barton, CHP [signature on file]

Kathleen Behling [signature on file]

Record of revisions

Revision number Effective date Description of revision

0 (Draft) 4/21/2023 Initial issue
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Table of Contents

List of Tables................................................................................................................... 4

List of Figures.................................................................................................................. 4

Abbreviations and Acronyms........................................................................................... 5

1 Statement of Purpose........................................................................................... 6

2 NIOSH’s General Approach to Determining Extremity dose................................. 6

2.1 Source of data.................................................................................................... 6

2.2 NIOSH’s analysis of data in ORAUT-OTIB-0087 ............................................... 6

3 SC&A’s Review of ORAUT-OTIB-0087 ................................................................ 7

3.1 SC&A’s evaluation of original Mound data used in OTIB-0087 .......................... 7

3.2 SC&A’s evaluation of tables 5-1 and 5-2 and figures 5-1 and 5-2 of OTIB-0087

......................................................................................................................... 11

3.3 SC&A’s statistical analysis ............................................................................... 12

3.4 SC&A’s evaluation of NIOSH’s recommendations ........................................... 12

4 Conclusions........................................................................................................ 13

5 References ......................................................................................................... 14

Attachment A: Summary of SC&A’s Statistical Analysis................................................ 15
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List of Tables

Table 1. Right and left wrist-to-WB gamma dose ratios as a function of operation ......... 9

Table 2. Right and left wrist-to-WB neutron dose ratios as a function of operation ....... 10

List of Figures

Figure 1. Wrist-to-WB gamma dose ratios, left and right hand........................................ 8

Figure 2. Right wrist-to-WB gamma dose ratios as a function of operation..................... 9

Figure A-1. Scatterplot of left wrist versus whole body neutron dose............................ 16

Figure A-2. Right wrist versus WB gamma dose – linear trendline ............................... 17

Figure A-3. Right wrist versus WB gamma dose – exponential trendline...................... 18

Figure A-4. Right wrist versus WB gamma dose – metallurgical evaluations................ 19

Figure A-5. Left wrist versus WB gamma dose – metallurgical evaluations .................. 20

Figure A-6. Right wrist versus WB gamma dose by operation type .............................. 21
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Abbreviations and Acronyms

ABRWH Advisory Board on Radiation and Worker Health 

DOE U.S. Department of Energy 

DR dose reconstruction 

EE energy employee 

FP fuel processing

LiF lithium-fluoride

mrem millirem

NIOSH National Institute for Occupational Safety and Health

n/p neutron-to-photon 

NTA nuclear track emulsion, type A 

ORAUT Oak Ridge Associated Universities Team

Pu plutonium 

TLD thermoluminescent dosimeter 

WB whole-body 

W(th) watts-thermal
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1 Statement of Purpose

To support dose reconstruction (DR), the National Institute for Occupational Safety and Health 

(NIOSH) and the Oak Ridge Associated Universities Team (ORAUT) assembled a large body of 

guidance documents, workbooks, computer codes, and tools. One of those documents is 

ORAUT-OTIB-0087, revision 00, “Extremity Doses for Mound Exposures to Plutonium-238”

(NIOSH, 2017; “OTIB-0087”), which provides information about and comparison of wholebody (WB), wrist, and finger doses. This information may be used to determine ratios to assist in 

the assignment of extremity doses. Some energy employees (EEs) at Mound were only assigned

WB dosimetry. However, the work they performed may have included handling or working 

around plutonium (Pu)-238, and it would be expected that the dose to the extremities (forearm, 

wrist, hand, or finger) would be elevated in comparison with the WB dose. If an EE’s extremity 

dosimeter results are available, those results should be used to assign dose to the cancer site on 

the extremity. If not, the extremity-to-WB ratio applied to the WB dose can be used to determine 

the dose to the cancer site on the extremity.

In October 2022, SC&A was tasked to review ORAUT-OTIB-0087, revision 00 (NIOSH, 2017).

2 NIOSH’s General Approach to Determining Extremity dose

2.1 Source of data

Mound initiated a study in September 1972 to determine the need for extremity monitoring for 

personnel involved in Pu-238 operations at the site (Bigler, 1973). Wrist badges suitable for 

determining both neutron exposure using nuclear track emulsion, type A (NTA) film and gamma 

exposure using lithium-fluoride (LiF) thermoluminescent dosimeters (TLDs) were selected. The 

workers who performed the operations were monitored for various lengths of time ranging from 

2 to 22 weeks with a 2-week dosimeter exchange frequency.

A study (Bigler & Phillabaum, 1973) was also performed in 1972 and 1973 with wrist and WB 

gamma and neutron dosimeters during work in gloveboxes where the workers were wearing 

leaded rubber gloves. The monitoring approach for detecting the gamma and neutron dose used 

the same monitoring approach (i.e., LiF TLDs and NTA film, respectively) as the other study. 

This study also involved taping TLDs to the fingertips on the second or third finger of each hand 

to be able to determine the gamma dose to the fingertips. The number of days the dosimetry was 

worn ranged from 3 to 10 days.

NIOSH used the information in these reports, “Extremity Monitoring Study of Personnel in 

Plutonium Operations” (Bigler, 1973) and “Wrist and Fingertip Dose Measurements for 

Plutonium-238 Processing Operations” (Bigler & Phillabaum, 1973), to determine the ratios of 

left wrist-to-WB and right wrist-to-WB for gamma and neutron exposures. Ratios for left fingerto-left wrist and right finger-to-right wrist gamma ratios for a limited number of applications 

were also developed.

2.2 NIOSH’s analysis of data in ORAUT-OTIB-0087

NIOSH used the Akaike information criterion to estimate the quality of the model relative to 

other models for the wrist-to-WB data available from Bigler (1973) and Bigler and Phillabaum 
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(1973). The following sections summarize NIOSH’s analysis of the gamma and neutron wrist-toWB dose data.

2.2.1 Wrist-to-whole body gamma dosimetry data analysis

The wrist-to-WB gamma dosimetry data for the left and right wrist are summarized in table 5-1 

of OTIB-0087 for 28 employees covering nine different operations involving the handling of 

Pu-238 at Mound. NIOSH found that the wrist-to-WB gamma dosimetry data were best 

represented using a Weibull distribution. Figure 5-1 of OTIB-0087 provides a summary plot of 

the fit comparison for the gamma wrist-to-WB ratio. NIOSH determined the Weibull distribution 

values were 1.3295 (shape of curve), 1.9271 (scale), and 0.3436 (location). 

2.2.2 Wrist-to-whole body neutron dosimetry data analysis

The wrist-to-WB neutron dosimetry data for the left and right wrist are summarized in table 5-1 

of OTIB-0087 for 28 employees covering nine different operations involving the handling of 

Pu-238 at Mound. NIOSH found that the wrist-to-WB neutron dosimetry data were best 

represented using a lognormal distribution. Figure 5-2 of OTIB-0087 provides a summary plot of 

the fit comparison for the neutron wrist-to-WB ratio. NIOSH determined the most appropriate fit 

to be a lognormal distribution with a geometric mean of 1.5796 and geometric standard deviation 

of 2.5414. 

2.2.3 Finger-to-wrist gamma dosimetry data analysis

The finger-to-wrist gamma dosimetry data for the left and right hand/wrist are summarized in 

table 5-2 of OTIB-0087 for six workers covering three different operations involving the 

handling of Pu-238 at Mound. NIOSH found that since the data are limited, a fit comparison 

could not be determined; therefore, NIOSH recommends the use of a normal distribution model. 

From the limited dataset, NIOSH calculated an average left-hand finger-to-wrist ratio of 3.18, 

with a standard deviation of 0.53, and a right-hand finger-to-wrist ratio of 2.76, with a standard 

deviation of 0.85. Unless it is known that a worker is right- or left-handed, NIOSH recommends 

that the higher ratio should be used (i.e., 3.18 with a standard deviation of 0.53). 

3 SC&A’s Review of ORAUT-OTIB-0087

SC&A evaluated the original recorded Mound data, their use in constructing tables 5-1 and 5-2 

and figures 5-1 and 5-2 of OTIB-0087, and the DR recommendations in section 6.0 of OTIB0087. SC&A also performed a statistical analysis of the available data. 

3.1 SC&A’s evaluation of original Mound data used in OTIB-0087

SC&A reviewed the tabulated Mound data (Bigler, 1973, PDF pp. 177–183; Bigler & 

Phillabaum, 1973, PDF pp. 203–206). SC&A found that, while the quantity of data was 

somewhat limited (data from 28 employees for determining wrist-to-WB ratios and data from six 

employees for determining finger-to-wrist ratios), the measurements were conducted using 

acceptable dosimetry methods. As illustrated in figure 1 of this report, there were variations in 

the resulting ratio values listed in table 5-1 of OTIB-0087. Similar results are listed for neutron 

wrist-to-WB dose ratios.
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Figure 1. Wrist-to-WB gamma dose ratios, left and right hand

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017).

SC&A reviewed the wrist-to-WB ratio values in view of the potential impact of different 

fractions of time the worker was exposed to Pu-238 sources compared to the fraction of time 

spent in the general radiation area. The wrist-to-WB dose data (Bigler & Phillabaum, 1973, PDF

p. 205) provide three situations where the fraction of time spent with the Pu-238 sources 

compared to the total monitoring time was provided. The time fraction ranged from 

approximately 11 percent to 40 percent. However, the data did not provide any apparent 

correlation between the fraction of time and the wrist-to-WB ratios for either gamma or neutron 

exposure. Therefore, SC&A reviewed the wrist-to-WB ratios to determine if there was a general 

correlation of ratio values to the operation the workers performed.

Figure 2 shows an example of the right wrist-to-WB gamma dose ratios as a function of 

operation. The number of pairs of right wrist-WB gamma dose data points is indicated by the 

n = number following the specific handling operation in the figure legend. There was a total of 

23 pairs for the right wrist-WB gammas doses because five of the 28 entries were listed as 

“N/M” (SC&A assumed that that meant “not measured”). 
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Figure 2. Right wrist-to-WB gamma dose ratios as a function of operation

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017).

SC&A obtained similar, but not identical, results for the left wrist-to-WB gamma dose ratios, as 

well as the left and right wrist-to-WB neutron dose ratios. Tables 1 and 2 summarize the wristto-WB dose ratios, from largest to smallest, as a function of operation. 

Table 1. Right and left wrist-to-WB gamma dose ratios as a function of operation

Position

Number of 

pairs of wristto-WB data 

points *

Average right 

wrist-to-WB 

gamma dose 

ratio

Average left 

wrist-to-WB 

gamma dose 

ratio

Vacuum hot press operation of Pu-238 discs 5 4.12 3.30

Pu-238 fuel processing 6 3.08 2.22

Metallurgical evaluations and studies involving 

encapsulation of Pu-238

4 1.87 2.94

Encapsulation and decontamination of Pu-238 

sources

3 1.37 2.37

Handle encapsulated and project Pu-238 sources 

outside of glovebox and move sources within 

plant

3 1.19 1.22

Audit of Pu-238 encapsulation process 2 1.18 0.78

Analytical determination of Pu-238 fuel used in 

sources

3 1.10 1.26
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Position

Number of 

pairs of wristto-WB data 

points *

Average right 

wrist-to-WB 

gamma dose 

ratio

Average left 

wrist-to-WB 

gamma dose 

ratio

Radiography and leak testing of Pu-238 sources 1 0.88 0.56

Handling of Pu-238 neutron sources 1 0.36 0.83

* There were several instances where the right or left wrist dose was listed as “N/A” or “N/M.” 

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017).

Table 2. Right and left wrist-to-WB neutron dose ratios as a function of operation

Position

Number of 

pairs of wristto-WB data 

points *

Average right 

wrist-to-WB 

neutron dose 

ratio

Average left 

wrist-to-WB 

neutron dose 

ratio

Metallurgical evaluations and studies involving 

encapsulation of Pu-238

4 2.94 11.11

Radiography and leak testing of Pu-238 sources 1 2.68 1.61

Vacuum hot press operation of Pu-238 discs 5 2.50 7.26

Pu-238 fuel processing 6 2.09 1.44

Audit of Pu-238 encapsulation process 2 1.78 0.60

Handle encapsulated and project Pu-238 sources 

outside of glovebox and move sources within 

plant

3 1.31 1.43

Encapsulation and decontamination of Pu-238 

sources

3 1.25 1.16

Analytical determination of Pu-238 fuel used in 

sources

3 1.19 1.81

Handling of Pu-238 neutron sources 1 0.29 0.50

* There were several instances where the right or left wrist dose was listed as “N/A” or “N/M.” 

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017).

Tables 1 and 2 indicate that the right and left wrist-to-WB ratios varied according to the type of 

operation being performed (for both gamma and neutron doses). This relationship is examined in 

more details in attachment A of this report.

The original Mound data (Bigler, 1973, PDF p. 182; Bigler & Phillabaum, 1973, PDF p. 206) 

provide lists of derived neutron-to-photon (n/p) ratios from WB, left wrist, and right wrist dose 

data. The n/p values have a wide range of 0.22 to 12.00; therefore, neutron along with gamma 

extremity dosimetry is needed because the use of an average n/p value instead of using neutron 

dosimetry could result in considerable errors in neutron extremity dose assignment. 

Finding 1: When applying ratios to other operating periods or DOE sites, NIOSH should 

have an understanding that the exposure conditions are similar to those used in 

OTIB-0087

Considering the variations in wrist-to-WB ratio values as a function of operation, it is important 

when applying the Mound extremity ratio values to DR from other operating periods at Mound 

or other U.S. Department of Energy (DOE) sites, as recommended in section 1.2 of OTIB-0087, 

to first ascertain that the conditions of exposure to Pu-238 during the other periods at Mound or 

at other sites are encompassed by the Mound operations. For example, leaded glove, as was used 

when the OTIB-0087 measurements were conducted, could influence the resulting ratios. If 
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leaded gloves were not worn during other operational periods at Mound or other sites, the 

measured ratios might not be applicable. 

It should also be noted that SC&A is aware that NIOSH is applying the OTIB-0087 ratios at 

other DOE sites. SC&A has reviewed a 2020 DR case that applied the wrist-to-WB dose 

methodology as recommended in OTIB-0087 for an EE who worked at the Pantex Plant and had 

potentially handled Pu-238. SC&A found that NIOSH correctly applied the recommendations in 

OTIB-0087 to that DR. However, the exposure conditions at the Pantex Plant were not analyzed 

in the DR report to indicate that they were similar to those at Mound to justify applying OTIB0087 to Pantex. 

3.2 SC&A’s evaluation of tables 5-1 and 5-2 and figures 5-1 and 5-2 of OTIB-0087

The gamma-ray energies listed in table 3-1 of OTIB-0087 were obtained from “Gamma 

Shielding Requirements for Plutonium-238 and Polonium-210” (Foster, 1966), and the neutron 

energy spectra in figure 3-1 of OTIB-0087 were obtained from “Neutron Flux, Spectrum, and 

Dose Equivalent Measurements for a 4500-W(th) 238PuO2 General Purpose Heat Source” 

(Anderson, 1985). These are typical for Pu-238 and reasonable to assume for dosimetry for the 

Mound extremity monitoring in OTIB-0087. SC&A analyzed the data in tables 5-1 and 5-2 of 

OTIB-0087 and compared them to the original Mound data (Bigler, 1973, PDF pp. 177–183; 

Bigler & Phillabaum, 1973, PDF pp. 203–206). SC&A found that the original Mound data were 

correctly entered in tables 5-1 and 5-2. However, SC&A did have the following two 

observations. 

Observation 1: Two entries from Mound data not located in OTIB-0087

SC&A found that NIOSH incorporated all six entries of the Mound data for finger-wrist-to-WB

exposure (Bigler & Phillabaum, 1973, PDF p. 205) into table 5-2 of OTIB-0087. Additionally, 

SC&A found that NIOSH incorporated the first four entries of the Mound data for finger-wristto-WB exposure into table 5-1. However, SC&A could not locate where NIOSH incorporated the 

last two entries of the Mound data for finger-wrist-to-WB exposure into table 5-1. The wrist-toWB ratio values for these two entries were very similar to the other wrist-to-WB ratio values in 

table 5-1; therefore, this would not greatly affect the results. However, it would be helpful for 

NIOSH to clarify why these last two entries appear to be omitted from table 5-1 of OTIB-0087. 

Observation 2: Discrepancies in number of ratios between table 5-1 and figures 5-1 

and 5-2 

There appear to be discrepancies between the data reported in table 5-1 and figures 5-1 and 5-2. 

For instance, figure 5-1 reports that there were 55 values used to construct the histogram and fit 

the Weibull curve. However, there are only 45 valid wrist-WB gamma ratios reported in table 5-

1. The mean ratio is reported as 2.116 in figure 5-1, but the mean of the wrist-WB gamma ratios 

in table 5-1 is 2.143.

Figure 5-2 reports that there were 53 values used to construct the histogram and fit the lognormal 

distribution. However, there are only 43 valid wrist-WB neutron ratios in table 5-1. Figure 5-2 

also lists minimum and mean values of 0.179 and 2.551, respectively. The minimum wrist-WB 

neutron ratio listed in table 5-1 is 0.27, and the mean wrist-WB neutron ratio in the table is 

2.502. 
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SC&A could not locate anything in OTIB-0087 that would explain the noted discrepancies.

3.3 SC&A’s statistical analysis

The sparsity and variation of the data in table 5-1 suggests that the estimated ratios in 

OTIB-0087 are likely quite imprecise. Thus, extremity dose estimates based on these ratios will 

be imprecise. An important step in validating the estimated distribution parameters and average 

ratio values in OTIB-0087 would be to estimate the precision of the statistics used in the 

analysis.

There are several issues that suggest the estimated ratios are imprecise:

1. Sparsity of data – A relatively small number of observations are used in the estimation; 

there is a total of 28 employee observations in table 5-1. From those, there are 45 valid 

wrist-WB gamma ratios and 43 valid wrist-WB neutron ratios. It should be noted that 

those observations are also interrelated because each employee potentially supplied two 

wrist-WB gamma and two wrist-WB neutron observations. This reduces the effective 

sample size to something less than 45 and 43, respectively.

2. Outliers – Some large outliers in the ratio measurements affect the ability to accurately 

fit empirical distributions.

3. Linear relationship – The use of ratios to estimate wrist doses from WB doses assumes

a linear relationship between the two types of doses. The linear relationship is not entirely 

evident from the data in table 5-1.

4. Operation type – There are indications that the relationship between wrist doses and WB

doses differs by operation type, which suggests the need for different estimated ratios by 

operation type for imputations to be valid.

It would be instructive to address these items that may contribute to imprecisions of the derived 

ratios. SC&A provides further analysis of the data related to these items in attachment A of this 

report. As a result of this analysis, SC&A had the following finding about the ratio values.

Finding 2: Use of upper bound may be more appropriate in dose reconstruction

Considering the issues with the data as summarized in this section and analyzed in attachment A, 

SC&A suggests that it would be more claimant favorable to use an upper bound ratio, such as the 

upper limit of the confidence interval, instead of a distribution or average ratio value. 

3.4 SC&A’s evaluation of NIOSH’s recommendations

Section 6.0 of OTIB-0087 recommends that when a worker was exposed to Pu-238 and an 

extremity dose is needed, the dose reconstructor should use the following dose ratios and dose 

distributions to calculate the extremity dose:

• To determine the gamma dose to the wrist, the dose reconstructor should use the Weibull 

distribution, shape of the curve equal to 1.3295, scale equal to 1.9271, and location equal 

to 0.3436, in conjunction with the gamma WB dose to determine the wrist dose.
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• To determine the neutron dose to the wrist, the dose reconstructor should use the 

lognormal distribution, with a geometric mean of 1.5796 and a geometric standard 

deviation of 2.5414, in conjunction with the neutron WB dose to determine the wrist 

dose. 

• When evaluating the finger-to-wrist extremity dose, use the average value of 3.18 times 

the wrist dose for the left finger dose and 2.76 times the wrist dose for the right finger. 

Since a meaningful fit could not be determined, assign data using a normal distribution. If 

it is not known if the worker was right or left-handed, use the greater of the ratios, 3.18. 

SC&A’s evaluation of the data presented in OTIB-0087 and related documents finds that the 

recommendations in section 6.0 of OTIB-0087 may be useful for DR purposes, but the 

recommended ratio values are imprecise as discussed in previous sections of this report and 

summarized in finding 2. 

4 Conclusions

SC&A evaluated the original recorded Mound data, its use in constructing tables 5-1 and 5-2, 

and the DR recommendations. SC&A also performed a statistical analysis of the recorded data. 

SC&A identified two findings and two observations:

• Finding 1: Caution when applying ratios to other operating periods or DOE sites 

• Finding 2: Use of upper bound may be more appropriate in dose reconstruction 

• Observation 1: Two entries from Mound data not located in OTIB-0087 

• Observation 2: Discrepancies in number of ratios between table 5-1 and figures 5-1 

and 5-2. 
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5 References

Anderson, M. E. (1985). Neutron flux, spectrum, and dose equivalent measurements for a 

4500-W(th) 238PuO2 general purpose heat source (MLM-3248). Monsanto Research Corporation, 

Mound, Miamisburg, Ohio. SRDB Ref. ID 003171, PDF pp. 54–68 

Bigler, W. A. (1973). Extremity monitoring study of personnel in plutonium operations. 

Monsanto Research Corporation, Mound Facility, Miamisburg, Ohio. SRDB Ref. ID 003281, 

PDF pp. 177–191 

Bigler, W. A., & Phillabaum, G. L. (1973). Wrist and fingertip dose measurements for 

plutonium-238 processing operations. Monsanto Research Corporation, Mound Facility, 

Miamisburg, Ohio. SRDB Ref. ID 003281, PDF pp. 203–206 

Foster, K. W. (1966). Gamma shielding requirements for plutonium-238 and polonium-210 

(revised) (MLM-1315). Monsanto Research Corporation, Mound Facility, Miamisburg, Ohio. 

SRDB Ref. ID 46890 

National Institute for Occupational Safety and Health. (2017). Extremity doses for Mound 

exposures to plutonium-238 (ORAUT-OTIB-0087, rev. 00). 

https://www.cdc.gov/niosh/ocas/pdfs/tibs/or-t87-r0.pdf

National Institute for Occupational Safety and Health. (2018). Applications of regression in 

external dose reconstruction (ORAUT-RPRT-0087, rev. 00). 
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Attachment A: Summary of SC&A’s Statistical Analysis

SC&A analyzed the four issues referred to in section 3.3 of this report that may contribute to 

imprecisions of the derived ratios: (1) sparsity of data, (2) outliers, (3) linear relationship, and 

(4) operation type. This attachment summarizes SC&A’s analysis and conclusions.

Sparsity of Data

It is understandable that there are not a lot of data to base practical procedures for imputing 

unmeasured doses at one bodily area from another. Unfortunately, with the small amount of data 

in table 5-1 of OTIB-0087, it is difficult to robustly determine a valid statistical distribution that 

resembles the true wrist-to-WB ratios that apply to all Pu-238 handlers. Additionally, even if the 

distributions could be adequately determined, fitting a statistical distribution that requires the 

estimation of several parameters is problematic. The parameter estimates are going to be 

imprecise, and data that do not fit well into the assumed distribution (outliers) compound the 

problem. 

Outliers

Related to the issue of the lack of data is the issue of outliers in the data. If we examine the left 

wrist neutron doses versus WB neutron doses from table 5-1 in the form of a scatterplot 

(figure A-1), a couple of things stand out. The first is that there are some points that are fit very 

poorly by the linear model, the basis of the ratio method. In particular, the two points in the 

upper left quadrant of the figure are far removed from the trendline. These points have an undue 

influence on the parameter estimates of the line; thus, they have the same undue influence on the 

ratios calculated by fitting a statistical distribution to the data.

The second thing that stands out is the strength of the linear relationship between the left wrist

and WB doses: The R2 value (0.40) for this trendline, on which the estimated left wrist-WB ratio 

is based on, is not very large. 
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Figure A-1. Scatterplot of left wrist versus whole body neutron dose

y = 1.2771x

R2 = 0.4037

0

1000

2000

3000

4000

5000

6000

0 500 1000 1500 2000 2500

Left wrist neutron dose (mrem)

Whole body neutron dose (mrem)

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017). 

Linear Relationships Are Not Necessarily Optimal

It may not be optimal to use simple ratio adjustments to impute for missing dose data. 

Relationships between doses at different areas of the body may be more complex than a simple 

ratio. For instance, a ratio connotes that there is a linear relationship between doses from two 

bodily areas that remains the same across individuals. However, even the limited data of this 

study indicate that such a relationship is not necessarily the best way to describe the association. 

For example, figure A-2 shows the right-wrist gamma dose measurements against the WB

gamma dose measurements for all individuals that had both measurements in table 5-1 of OTIB0087. While the linear relationship between the two measurements is strong, there is greater 

evidence of a nonlinear relationship. The trendline in figure A-3 models an exponential 

relationship between the two. The practical importance of this is that predictions of right-wrist 

doses from WB doses on a case-by-case basis are going to be better with a model, such as using 

an exponential relationship, instead of a simple ratio. However, because of the sparsity of data, 

the most conversative method is to use a bounding approach as indicated in finding 2 for both the 

right and left hand-to-WB ratios. 
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Figure A-2. Right wrist versus WB gamma dose – linear trendline

y = 2.1417x

R2 = 0.86

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

0 200 400 600 800 1000 1200

Right wrist gamma dose (mrem)

Whole body gamma dose (mrem)

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017). 
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Figure A-3. Right wrist versus WB gamma dose – exponential trendline

y = 106.39e0.0034x

R2 = 0.9389

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

0 200 400 600 800 1000 1200

Right wrist gamma dose (mrem)

Whole body gamma dose (mrem)

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017). 

Operation Type

One complexity that would be difficult to account for with simple ratios is dosage relationships 

that differ by type of operation. It’s difficult to tell from such a sparse data set, but looking at the 

measurements from the four employees involved in metallurgical evaluations gives a different 

picture than that obtained from the entire dataset. Figures A-4 and A-5 display the right wrist 

versus WB and left wrist versus WB gamma doses measured for the employees involved in 

metallurgical evaluations. (Note: Only two of the employees registered left wrist measurements 

and three registered right wrist measurements.) These graphs suggest a relationship different than 

the overall relationship shown in figure A-2. 

This is partly a problem with using the small data set and partly a potential issue due to 

complexity. The small data set does not allow us to fully grasp the differences between types of 

operations, but it does indicate the possibility that the ratios for metallurgical evaluations are 

different from those of other operations.
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Figure A-4. Right wrist versus WB gamma dose – metallurgical evaluations

0

100

200

300

400

500

600

700

800

900

1000

0 50 100 150 200 250 300 350 400 450 500

Right wrist gamma dose (mrem)

Whole body dose (mrem)

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017). 
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Figure A-5. Left wrist versus WB gamma dose – metallurgical evaluations

0

100

200

300

400

500

600

700

800

900

1000

0 50 100 150 200 250 300 350 400 450 500

Left wrist gamma dose (mrem)

Whole body gamma dose (mrem)

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017). 

Another way to think about this is to graph right wrist dosage by WB dosage for each operation 

type side by side, as in figure A-6. In this figure, each pane in the figure displays the right-wristby-WB gamma dosage for a different operation type. It is clear from this graph that the fuel 

processing (FP) data drive the linear relationship observed in the overall graph (figure A-2). If 

we removed the FP data from the analysis, we would get a very different picture of the 

distribution of right-wrist-to-WB gamma ratios and a very different estimated ratio for rightwrist-to-WB gamma doses.
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Figure A-6. Right wrist versus WB gamma dose by operation type

 

Source: Table 5-1 of OTIB-0087 (NIOSH, 2017). 

Other and Similar Work

SC&A noted that the quantile regression work in ORAUT-RPRT-0087, revision 00, 

“Application of Regression in External Dose Reconstruction” (NIOSH, 2018), modeled the 

components of ratio relationships differently. One dose was used to predict for the other in a 

more complex way. While the basis of the relationship was still linear in that work, a parametric 

distribution was not overlaid on the relationship. Additionally, and importantly, the predicted 

relationship was allowed to vary at different quantiles of the distribution. These are two concepts 

that might be effectively exploited in an extension of OTIB-0087 for modeling extremity doses 

in relationship to WB doses, if there were adequate data to support the model.