oe Lhe” a » 4 ed BROOKHAVEN NATIONAL LABORATORY i 4 ASSOCIATED UNIVERSITIES, INC. iia dd 1 4 4 4 Upton Long island, NewYork 11973 (516) 282. FTS 666° Safety & Enwronmental Protection Divisicn 4250 May 2, 1983 Mr. Charles B. Meinhold, Head Safety & Environmental Protection Division Brookhaven National Laboratory Upton, New York 11973 Dear Charlie: This is in response to your request to review portions of a report of Task Group 7 of Scientific Committee 5/7 entitled, "“Thyroidal Carcinogenesis Following Exposure to Ionizing Radiation". I am familiar with background material related to estimates of thyroid absorbed dose to Rongelap and Utirik Atoll residents who were exposed as a result of the U.S. Pacific Weapons Testing Program. Specifically, my colleagues and I have reassessed thyroid ahsorbed dose. Details of the methods for the reassessment are in draft form and are going through initial review. Rasults of the study, which are tentative, are given in Table One. I have consulted with the Marshal! Islands Medical Program Director, William Adams, M.0. in order to determine the total number of people and the total thyroid effects since the time of exposure, March 1954. These data are given also in Table One. The data include the most recent thyroid nodules detected in the exposed population. Or, Adams and I estimated the excess cases of nodules and thyroid cancer based on Robert Conard's twenty-six year report (Co80). However, thyroid cancer and nodule data from the Marshallese comparison populations are being thoroughly re-examined by us due to possible low-level exposure of some of these people from the testing program. The average time at risk per irradiated subject was assumed to be the time from radiation expasure on March 1-3, 1954 to time of surgery. OQne person in the Utirik exposed population was assumed not to be an excess thyroid cancer. Debate continues and a clear distinction of either carcinoma or adenoma for this individual may never be resolved. One implication of the dose reassessment was that the thyroid dose to each population (see Table One) was from different relative amounts of external and internal radiation. Also, the internal radiation dose rete was different for each atoll population due to differences in nuclide composition as a function of fallout age. The greatest portion of thyroid ahsorbed dose was reassessed to be from the shorter lived iodine isotopes [-133 and I-135 and not from I-131.