Nagasaki persons who received greater than 50 rad (CBEIR80). A value of 220 per
million person-gray-years (2.2 cancers per million person-rad-years) was
reported for individuals exposed at Hiroshima (CBEIR80).
A group of 2611 people
who were irradiated during the first year of life for presumed enlargement of
the thymus gland exhibited an incidence of 290 per million person-gray-years
(2.9 cancers per million person-rad-years) (CBEIR80). The University of Chicago
head and neck irradiation sample of 100 children irradiated at about 4.5 years
of age resulted in a risk of thyroid cancer of about 400 per million persongray-years (4 cancers per million person-rad-years) (CBEIR80). The Michael
Reese Hospital head and neck irradiation sample of 2109 people irradiated during
infancy, childhood, or adolescence exhibited a thyroid cancer risk of 210 per
million person-gray-years (2.1 cancers per million person-rad-years) (CBIER80).
A person-weighted average of the above values gives a combined risk of about 200
per million person-gray-years (2 thyroid cancers per million person-rad-years).
Thus, the comparison of risk from Marshall Islands fallout studies to external
irradiation studies involving instantaneous doses to the thyroid showed no significant difference.
Scalp irradiation of over 10,000 Jewish children resulted in an absolute
risk estimate of 630 per million person-gray-years (6.3 thyroid cancers per mil
lion person-rad-years) (CBEIR80). Another study of 261 Jewish persons
irradiated during infancy for presumed enlargement of the thymus resulted in a
risk of 480 per million person-gray-years (4.8 thyroid cancers per million person-rad-years) (CBEIR80). Comparison of our value to Jewish populations showed
no statistically significant difference due to variations in doses estimated in
either of the exposed groups (Ha52).
Studies’ of children exposed to fallout radioiodine in Utah and Nevada have
not revealed any excess thyroid cancers (CBEIR80).
There is no evidence to dem-
onstrate a carcinogenic effect in people following intake of 131 for treatment
of hyperthyroidism (CBEIR80). No value of risk can be estimated for
I exposure on the basis of Marshall Islands experience. This is because the internal
dose to the Marshallese thyroids from 1311 amounted to about 10 to 20% of the
total thyroid dose. The beta to gamma dose ratio from the BRAVO mixture of iodines plus external radiation was not similar to 1317, 3.5 versus 7.5 respectively.
Another major difference between 131; exposure and the Marshallese exposure was dose rate.
D.
Estimate of the Uncertainty in the Derived-Risk Estimate
In order to estimate the uncertainty in the derived risk estimate the fol-
lowing argument was used.
ask
Ri
=
# of effects
dose x # of years at risk
.
=
a
be
e
(1)
The uncertainty in the risk, A Risk, is approximately the sum of the products of the uncertainties in a, b or ¢ times the effect that a, b or c have on
the value of risk (Be69).
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