ee “7 Sr Nagasaki persons who received greater than 50 rad (CBEIR80). nate Meanie 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 person- gray-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 sig~ nificant 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 demonstrate a carcinogenic effect in people following intake of 13lr for freatment of hyperthyroidism (CBEIR80). No value of risk can be estimated for 13!1 expo- sure 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 131t, 3.5 versus 7.5 respec— tively. Another major difference between l3ly 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 following argument was used. ae # of effects = 2a Risk dose x # of years at risk be ° (1) The uncertainty in the risk, A Risk, is approximately the sum of the pred- ucts of the uncertainties in a, b or c times the effect that a, b or c have on the value of risk (Be69). ouGlohgs a Cc - 65 -