Transcript Slide 1

ESTIMATES OF RISKS
FROM RADATION EXPOSURES
MEETING OF NORTH CAROLINA
CHAPTER
HEALTH PHYSICS SOCIETY
Dade W. Moeller
October 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 supralinear 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 radionuclides 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
Pu, and 241Am
226Ra, 237Np, 239
• 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)
Bladder 0.50
Bone
0.72
Bone
0.99
marrow
Breast
0.50
Ovary
0.70
Thyroid 0.10
ICRP 103 Factor of
(2007) Reduction
0.29
1.7
0.45
1.6
0.67
1.5
0.29
0.57
0.07
1.7
1.2
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


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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


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
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
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today will have been achieved within 20 to 30 years
CASE #1
INFLUENCING FACTORS
RADIONUCLIDE SPECIFIC

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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 #2
CONSIDERATIONS
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 #2
INFLUENCING FACTORS
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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

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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 #2
OVERALL 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 #3
PROVIDING 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 #3
CONCLUSIONS

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 #3
PROVIDING 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 Corresponding Dose to the Workers at All the U.S.
Nuclear Electric Generating Plants and
Nuclear Installations of the U.S. Department of Energy, plus the Crews on All the
Nuclear-Powered Submarines and Surface
Vessels of the U.S. Navy
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