United States Scientific Perspectives onRadiation Risk to Populations from Large-scaleRadiation Events
Darrell R. Fisher
Health Physics Society

July 2, 2015
Arakawa Campus of Tokyo Metropolitan University

Richland: Home to WNP2Columbia Generating Station: 1,170 MWe
GE BWR-5 using a Mark II containment structure

2

2014

Addressing difficult challenges
 As radiation professionals, we deal with radiation
emergencies
 Our broad science backgrounds and passion for technicalaccuracy:• help us put into proper perspective the relative
magnitude of an incident,• provide us with methods for making correct radiation
measurements and analyzing data, and• help us to determine engineered solutions for site
recovery and waste management, containing andshielding radioactivity, packaging, transportation, anddisposal

We balance our perspectives onradiation risks and benefits
Our scientific perspective of radiation risks and healthdetriment, judged against the societal benefits of nuclear
technologies, engenders credibility, and facilitateseffective communication when dealing with government
officials, the news media, and the publicrisks

benefits

The principal issue today: risk
• What is the shape of the dose-response function at low
doses and for low dose-rates?
• How does our understanding of dose-response functionstranslate to assessment of individual radiation risk?

Stated in other ways
• Is there a “safe” level of radiation exposure?
• Is there a safe level “below regulatory concern”?
• Are small amounts of radiation more beneficial thanharmful? What does it mean for emergency response?

Related issues• Dose and dose-rate effectiveness factor• Adaptive response and other risk-modifying factors• Risk coefficients (cancer induction)• Deterministic effects: dose to lens of eye• Correct use of effective dose
• Emergency response guidelines

Hiroshima-Nagasaki
Atomic Bomb Survivor
Data, U.S. National
Academy of Sciences
Report, Biological
Effects of IonizingRadiation(BEIR VII) report,
2008.

Hiroshima-Nagasaki Atomic
Bomb Survivor Data, U.S.
National Academy of Sciences
Report, Biological Effects ofIonizing Radiation(BEIR VII) report, 2008.

We do notknow theactual risks
at very lowlevels

Adaptive response to low-dose radiation•As with some chemical agents, low doses of ionizing
radiation (1 cGy) can induce mechanisms whereby cells
become better able to cope with subsequent exposures
to high doses (1.0 Gy) of radiation
Example: Chromosome aberrations in cultures of human
lymphocytes were reduced by 50%(S. Wolf, Environ Health Perspectives 106:277; 1998)

60

Inhaled plutonium-239 oxide inbeagle dog lungs

Lung Tumor Incidence, Percent

50

Fisher and Weller, Health Phys.
99(3):357–362; 2010
40

n=8n = 1130n = 28
20n = 10slope = 2390 lung tumors/106 dog cGy
Ŷ = 2.39 x 10-3 (X) - 0.026, r = 0.98

1000n = 1650

100-10
Cumulative Absorbed Dose to Lungs (cGy)

150200Leuraud, Richardson, Cardis et al., Lancet
Haematol online June 22, 2015

ERR = 2.96 Gy-1
• Negative for
lymphoma and CLL

A major (but simple error) occurred in the publication by
K. Leuraud et al. in Lancet Haematol. 2015):
The authors failed to consider the increase in medical
radiation dose (e.g. from CT scans) that occurred during
1944-2005, the period of the study.
It was during this period of time that medical exposuresincreased and occupational exposures decreased.

Some problems with the linear no-thresholdhypothesis• The BEIR VII linear model assumes that the risk frominstantaneous high dose rates from theHiroshima/Nagasaki bomb data (gamma rays plusneutrons) is equivalent to the risk from protracted
low-dose-rate, internally deposited (beta plusgamma-emitting) radionuclides• The linear no-threshold hypothesis may not hold forvery low doses of radiation• An increasing dominant body of scientific evidence
contradicts the linear non-threshold modelSome problems with the linear no-threshold
hypothesis (continued)• The risk coefficients obtained therefrom have highuncertainty at very low doses• Cancer is a low-probability event, so the linear modelcannot predict individual risk

• Actual risks vary with cell type, biological end-point,
radiation quality, age and sex, and competing risks• The LNT hypothesis does not permit one to define what
constitutes a “safe” radiation exposure
Conclusion: We do not know the actual risks of cancer atvery low doses

Report: Anti-Nuclear Regulations Based onFalse Science, Lies

by Gene Koprowski
The Heartland Institute, June 10, 2015
WASHINGTON — A new report by the conservative Capital Research Center (CRC)
indicates that the U.S. government’s policy on radiation exposure is premised upon“irrational fear” and “discredited science,” and denies Americans easy access totechnology that could reduce the cost of electricity. The Green Watch report fromCRS, entitled, Fear Itself, was distributed toconservative activists at a background briefing
near Capitol Hill this morning. Called the“Linear No Threshold” theory by theEnvironmental Protection Agency (EPA), theOccupational, Safety and HealthAdministration (OSHA) and allies on theenvironmental Left, the theory posits that “anytiny amount” of radiation will kill “somenumber” of people per every million or billion
exposed. “The idea, in essence, is this,” theJune 2015 report indicates, “If 100 aspirins
would kill the average person, then the same
person would be killed by taking 100 aspirin
at the rate of one a day for 100 days, or, if one
day, 100 people each took one aspirin, then one of those hundred people would die.”
The theory was put forth in the 1930s by a geneticist, Hermann Muller, who was anardent socialist, and was guilty about working on the Manhattan Project to create theProblems with radiation regulation
using the linear no-threshold hypothesis• Regulatory systems are “linear” and cannot
accommodate any other model• Primary and secondary standards for radiation
protection are based on the linear model• Regulatory systems assume that the linear modelholds exactly at low doses, whereas substantial
scientific evidence shows that this is not the case• We cannot accurately measure, assign, and record
radiation dose at low (background radiation) levels

Recent U.S. citizen petition for rulemaking
June 23, 2015. Federal Register
The Nuclear Regulatory Commission received threepetitions for rulemaking requesting that the NRC amend its‘‘Standards for Protection Against Radiation’’ and change
the basis of those regulations from the Linear NoThreshold (LNT) model of radiation protection to theradiation hormesis model.
The radiation hormesis model provides that exposure of
the human body to low levels of ionizing radiation isbeneficial and protects the human body . . .

Dose and dose-rate effectiveness factor
A correction factor (DDREF) has been proposed to convert
risk determined at relatively high doses and dose rates torisk at low doses (less than 100 mGy) and low dose-rates(less than 5 mGy per hour)

DDREF = 2.0 (ICRP Publication 60, 1991)
DDREF = 1.5 (BEIR VII Report, 2006)

DDREF = 1 to 2 (NCRP Report 171, 2012)
We do not know the DDREF with confidence!

Dose and dose-rate effectiveness factor
Ozasa et al., Atomic BombSurvivors Report 14,
Radiat. Res. 177:229-243;
2012“The Dose and Dose-rate Effectiveness Factor(DDREF) is defined by dividing the slope of anon-linear function at low dose levels by the slopeof the extrapolated linear non-threshold function . . .
So this upward curvature may imply a DDREF
greater than one.”

“The apparent upward curvature appears to berelated to relatively lower than expected risks inthe dose range 0.3 - 0.7 Gy, a finding without
current explanation.”-- Ozasa et al., Atomic BombSurvivors Report 14, Radiat. Res.
177:229-243; 2012

Prospective risk assessments• Cancer risk coefficients may be obtained directly fromthe dose-response function• It is a common practice to use the risk coefficients forpredicting radiation risk in other populations exposed to:• environmental exposure to radiation sources• radiation at nuclear power plants• medical diagnostic radiological exams
If the dose-response function at low dose is highly
uncertain, then what is the value of a prospective risk
assessment derived therefrom?

Nominal risk coefficients x 10-2 Sv-1
ICRP Publication 60, 1990 (cancer mortality)
ICRP Publication 103, 2007 (cancer incidence)

Population
Whole
Adults onlyCancer
ICRP ICRP
103
60
5.5
6.0
4.1
4.8

Heritable
ICRP ICRP
10360
0.2
1.3
0.1
0.8

Total
ICRP ICRP
10360
5.7
7.3
4.2
5.6

Calculation: person•Sv x risk (10-2 Sv-1 ) = expectedcases in a population

Implied cancer risk*
Procedure

Effective
Dose (mSv)

Risk(4x10-2 Sv-1)

Head CT

21/12500

Abdominal CT

101/2500

Heart CT angiography

201/1250

Chest x-ray

0.1

1/250,000

Upper gastro-intestinal fluoroscopy

51/5000

Angioplasties

51/5000

Stents40

1/625

Diagnostic arteriography

71/3571

Cardiac percutaneous intervention

23

1/1087

F-18-Fluorodeoxyglucose

14

1/1786

Tc-99m-MDP bone scan

6.3

1/3968*not for individual risk analysis

Comparable risks: Lifetime risk ofdeath from everyday activities
Activity

1/riskExamination

1/riskRiding in a car

304

Crossing the street652

CT abdomen (10 yr)

1600

Choking on food894

CT abdomen (40 yr)

2900

Drowning

1127

18FDG-PET (10 yr)

1515

Falling down stairs

2024

18FDG-PET (40 yr)

2700

Riding bicycle

4734

99mTC-MDP (10 yr)

2560

Airplane crash

7058

99mTC-MDP (40 yr)

4760

Hit by lightning

84,388From Fahey et al, J Nucl Med, 2011

Conclusion: It is not appropriate to
extrapolate cancer risks obtained from one
organ or tissue, biological end-point, doserate, and cancer type to another organ ortissue, end-point, or cancer type“Misuse of the linear no-threshold model
for predicting radiation effects in exposed
individuals and populations should bediscontinued.”-- Siegel JA and Stabin MG,
Health Physics 102(1):90-99; 2012

Equivalent dose, HT (ICRP 60)

HT = ∑wR DT,R(to an organ or tissue)

where DT,R is the absorbed dose (averaged over a tissueor organ T) due to radiations of type R, and wR is theradiation weighting factor• DT,R can not be measured experimentally• The weighting factor adjusts absorbed dose forbiological effectiveness

Unit: J kg-1 (not a physical quantity)
Special name is sievert (Sv)

Effective dose, E (ICRP 60)
E = ∑wTHT = ∑wT ∑wR DT,R
where wT is a tissue weighting factor to adjust for total
detriment to health• Effective dose represents a doubly-weighted surrogate
of risk based on energy imparted multiplied by twocorrection factors

Unit: J kg-1 (not a physical quantity)
Special name is sievert (Sv)Problems with the concept of effective dose
• Represents a “surrogate” of risk; it is not a physicalquantity• Not a good measure for retrospective risk analysis• Designed only for establishing radiation protection
standards• Presupposes validity of the linear model• Applies only to an age-averaged, sex-averaged (maleplus female), region-averaged population group Does not apply to individual medical patients
 Cannot be used to predict individual risk
 Cannot predict population risks at low doses

Deterministic effects• Tissue reactions (ICRP 2012) due mainly to cell killing• Examples: radiation skin burns, ulceration, necrosis• Characterized by a clinical threshold dose
• Severity increases with dose
• Effects may appear from minutes to weeks• Chronic changes (over months) may be due to fibrosis andsmall blood vessel narrowing or occlusion leading tonecrosis• Sensitivity and expression vary with age at exposure(UNSCEAR 2013)

Dose to lens of eye
Vision-impairing cataracts may occur after high radiation
doses (more than 5 Gy) to the lens of the eye
Radiation cataracts may sometimes be differentiatedfrom senile cataracts by first appearing in the posterior
aspect of the lens

Dose to lens of eye• The ICRP recommended a large reduction in dose
limits to the lens
• Previous limit: 150 mSv• New limit: 20 mSv per year averaged over fiveconsecutive years, and 50 mSv in any single year

Is this change in dose limits justified?

Position of the Health Physics Society andNCRP Scientific Committee 1-23
• It is not clear that the proposed ICRP dose limit isjustified by scientific data
• Recent data on threshold appearance (0.5 Gy) apply tolens opacities, not cataracts• Supporting studies lack robust dosimetry• Dose fractionation alters the biological response• Cataracts may be corrected surgically (and does not
represent a life-threatening risk to health)• New dose limits will impact ability of radiologists toperform essential medical procedures
Conclusion: the change is premature and not based onsufficient scientific evidenceEmergency response• Effective dose is not an accurate predictor of future riskof cancer for individuals or populations• Emergency response actions should never be basedon statements involving estimated future risk of cancer
to workers or to the public• Regulators need to begin thinking in terms of “safe” or“not harmful” dose levels

Thank you!
I haveenjoyedmeeting withthe Japan
HealthPhysics
SocietyKanazawa Park 2014