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ESTIMATES OF RISKS FROM RADATION EXPOSURES

MEETING OF NORTH CAROLINA CHAPTER

HEALTH PHYSICS SOCIETY

Dade W. MoellerOctober 22, 2009

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ICRP PUBLICATION 103 (2007)

NEW INFORMATION: Item #1• Although the concept of collective dose should be retained as a prudent regulatory tool for dose and risk assessment, it should not be used for assessing risk, especially in terms of the hypothetical numbers of cancer cases involving small doses to large numbers of people over long periods of time

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ICRP PUBLICATION 103 (2007)

NEW INFORMATION: Item #2

• Although the health effects of low levels of exposure are still not known, there is no weight of evidence to support the concept that there is either a supra-linear response in this region, or that one for a low-dose threshold should be preferred for purposes of radiological protection

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ICRP PUBLICATION 103 (2007)

0THER INFORMATION: Item #3

• Environmental standards adequate to protect the general public will ensure protecting other species• The role of the stakeholder is as a decision aider• The role of the role of the regulator or other authority is as the decision maker• Interactions with stakeholders serve primarily as a means to enable the public to have input, although public acceptance is also important

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ICRP PUBLICATION 103 FOLLOW-UP REVELATIONS

• Many ICRP members believe that there is strong evidence for the existence of a practical threshold for cancer induction by all internally deposited alpha emitting radionuclides (226Ra, 239Pu, etc.)• This position, if implemented, would be a significant departure from previous ICRP positions • This pronouncement is based on epidemiological studies by Evans (1974) and the Los Alamos National Laboratory (1995)

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DOCUMENTATION FOR 226Ra (Evans, 1974)

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ESTIMATES OF A THRESHOLD DOSE FOR 226Ra • The studies by Evans, conducted at MIT

during the early 1930s and 1940s, primarily involved radium dial painters who ingested 226Ra and 228Ra while working in CT and NJ

• Applying an alpha radiation weighting factor of 20, the threshold dose (1,000 rad) was equivalent to 200 Sv

• Applying a tissue weighting factor for the bone marrow of 0.12, the corresponding effective dose was 24 Sv (2,400 rem)

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DOCUMENTATION FOR 239Pu (LANL)

• The intake limit for 239Pu, set in 1944, was based on the 226Ra data• Subsequent reviews, conducted by scientists at the Los Alamos National Laboratory, documented that not one of their workers had ever suffered any ill effects• On this basis, they concluded that this implied that 239Pu also had a threshold • This, however, could not be confirmed since the threshold was never reached

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CONSIDERING OTHER RADIONUCLIDES

Yucca Mountain Repository Regulated radionuclides: 14C, 99Tc, 129I, 228Ra, 226Ra, 237Np, 239Pu, and 241Am Realistic analyses show that none of these would be a source of exposure to the public

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THINKING OUTSIDE THE BOX

There is more to the assessment of the

health impacts of individual radionu- clides than simply estimating their dose dose rates Each one has unique characteristics that, depending on the circumstances, can significantly affect its health

impacts

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KEY FACTORS FOR EACH RADIONUCLIDE

Carbon-14• The average adult daily intake of stable carbon is 300 grams• This dilutes the maximum intake of 14C by 25 trillion to one• The result is that there is little, if any, risk due to intakes of this radionuclide

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KEY FACTORS FOR EACH RADIONUCLIDE Technetium-99

• Its biological half life is 3 days

• Its chemical nature is such that it will be immediately precipitated upon leaving the repository environment and entering the ground water

•The risk is neglible

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KEY FACTORS FOR EACH RADIONUCLIDE

Iodine-129• It has a physical half-life of 15 x 106 years• It caused no problems at Chernobyl• NCRP Report No. 80 states that its limitations “suggest that 129I does not pose a meaningful threat of thyroid carcinogenesis in people”

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KEY FACTORS FOR EACH RADIONUCLIDE

Radium-228• It has a physical half-life of 5.75 years and emits beta particles• It will have essentially completely decayed 100 years after being disposed• One could logically question why it was included in the list

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KEY FACTORS FOR OTHER RADIONUCLIDES

226Ra, 237Np, 239Pu, and 241Am• All of these emit alpha particles• As soon as the ICRP formally announces its intention to declare that they have relatively high thresholds for health effects, the estimated risks will be significantly reduced, if not eliminated

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THE FUTURE OF RADIATION RISK ASSESSMENTS THREE POTENTIAL

ASSESSMENT SITUATIONS #1: Exposures occurring now #2: Exposures that may occur in the future #3: Exposures whose effects are synergistically enhanced by other carcinogens

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REASON FOR SITUATIONS #1 AND #2

TEMPORAL RELATION• There is a temporal relation between dose and its associated risk• The reason is that the rates of cancer incidence and associated deaths is being reduced

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TEMPORAL RELATIONS

TRENDS IN CANCER RATES• From 2002 - 2004, the annual overall death rate from cancer among members of the U.S. public was reduced by an average of 2.1%; from 1993 - 2001, the reduction was 1.1% • Colorectal cancer, the 2nd leading cause of U.S. cancer deaths (after lung) is being reduced by ~5% for men, and ~4.5% for women

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TEMPORAL RELATIONS

TRENDS IN CANCER RATES• Between the early 1950s and 2009, the percentage of U.S. smokers was reduced from almost 50% to 20%.• Projections are that methods for the prevention and/or cure of the major cancers afflicting the U.S. population today will have been achieved within 20 to 30 years

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REDUCTIONS IN CANCER LETHALITY FACTIONS

(ICRP) Organ ICRP 60

(1990)ICRP 103 (2007)

Factor of Reduction

Bladder

0.50 0.29 1.7

Bone 0.72 0.45 1.6

Bone marrow

0.99 0.67 1.5

Breast 0.50 0.29 1.7

Ovary 0.70 0.57 1.2

Thyroid

0.10 0.07 1.4

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IMPLICATIONS

It is impossible to predict the risks (excess cancer incidence and deaths) due to radiation exposures more than about a decade into the future

Nonetheless, it is almost certain that the risks will be dramatically reduced

This will have a significant impact on the health risks of radiation exposures

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BACKGROUND ON SITUATION #3

Epidemiologists have discovered

that radiation can interact with chemical carcinogens to yield synergistic effects

These effects can have profound impacts, particularly those involving alpha emitting radionuclides (i.e., 210Po)

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SYNERGISTIC EFFECTS

For cigarette smokers, this combination can increase the risk of lung cancer by a factor of 8 to 25

Once again, this emphasizes the need to consider a range of factors in evaluating the risks of radiation

It also emphasizes the importance of ensuring continuing progress in cancer prevention and treatment

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CLOSING COMMENTARY

The field of risk assessment is undergoing rapid change

This will require the application of new approaches and concepts to what has, for years, remained a rather static field of endeavor

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ESTIMATES OF RISKS FROM RADATION EXPOSURES

THANK YOU FOR YOUR ATTENTION

Dade W. Moeller

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TRENDS IN CANCER RATES

Between 2002 and 2004, the overall death rate from cancer among members of the U.S. population was reduced by an average of 2.1% per year. From 1993 to 2001, the reduction was 1.1% per year

The current annual rate of reduction in colorectal cancer, the 2nd (behind lung cancer) leading cause of U.S. cancer deaths is ~5% for men, and almost 4.5% for women

Between the late 1940s and 2009, the percentage of U.S. smokers was reduced from almost 50% to 20%.

Projections are that methods for the prevention and/or cure of the major cancers afflicting the U.S. population today will have been achieved within 20 to 30 years

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CASE #1INFLUENCING

FACTORS RADIONUCLIDE SPECIFIC

Stable Element Intake: 14C Effective Half Life & Chemistry: 99Tc Half Life & Potential Effects: 129I & 228Ra Threshold Effects: 226Ra & 239Pu Impacts of Long Effective Half-Lives on Committed Doses: 237Np, 239Pu, & 241Am

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CASE #2CONSIDERATIONS

RELATION OF DOSE TO RISK In providing its Guidance on the

Standards for Yucca Mountain, the NAS Recommended that the Limits be Expressed in Terms of Risk

The Reason was that, as Progress in the Development of Methods for the Prevention and Cure for the Cancers are Achieved, the Risk per Unit Dose will be Correspondingly Reduced

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CASE #2INFLUENCING

FACTORS

Lung Cancer: Cigarette Smoking Colorectal Cancer: Colonoscopies Skin Cancers: Population Composition Cervical Cancers: Vaccinations Breast Cancers: Age of Mother at First

Child All Cancers: Obesity

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CASE #2 U.S. CANCER TRENDS

The annual rate of reduction in lung cancer (the #1 cause of cancer deaths) is following that of the reduction in cigarette smoking, from almost 50% in the early 1950s to 21% today

The annual rate of reduction in colorectal cancer (the #2 cause of cancer deaths) is almost 5% for men, and almost 4.5% for women; this is with only half of the eligible population receiving colonoscopies

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CASE #2OVERALL CANCER TRENDS

Between 1993 and 2001, the overall annual death rate from cancer among members of the U.S. population was reduced by 1.1%; Between 2002 and 2005, it was reduced by 2.1%

A 2008 poll of cancer specialists indicated that, methods for the prevention and/or cure of the major cancers that afflict the U.S. population, would be achieved within the next 20 to 30 years

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CASE #3PROVIDING PERSPECTIVE

The NCRP estimates that the

Radioactive Materials (including 210Po and 210Pb) in Cigarettes Yield an Average Annual Effective Dose to U.S. Smokers of 0.30 mSv

This is 30% of the limit for a member of the U.S. public and the Dose is Primarily Limited to 15% of the Population

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CASE #3 PROVIDING

PERSPECTIVE Localized Doses to the Bronchial Epithelium are Extremely High

It would require a Non-Smoker to have 2,000 chest x-ray Exams each year (more than 5 per day) to maintain the same dose rate

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CASE #3CONCLUSIONS

This led Michael J. Tidd (Journal of

the Royal Society of Medicine, June, 2008) to Conclude that:

“Smokers are killed by alpha-radiation, whatever its origin. Arguably, a significant part of this mortality is a result of Po-210 in tobacco”

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CASE #3PROVIDING PERSPECTIVE

Based on a total of 45 million U.S.

smokers, their Collective Dose is 13,500 person-Sv

This is More than 36 times the Correspond-ing Dose to the Workers at All the U.S. Nuclear Electric Generating Plants and Nuclear Installations of the U.S. Depart-ment of Energy, plus the Crews on All the Nuclear-Powered Submarines and Surface Vessels of the U.S. Navy