III. A. THYROID NODULES AND THYROID CANCER RISK FROM FALLOUT Tabulation of Thyroid Effects and Age at Exposure Medical records were reviewed by Adams of the Marshall Islands Medical Program for age at exposure and thyroid nodule data. Conard had performed a similar tabulation (Co80). Memoranda between the evacuation teams and their superiors were reviewed for age-at-exposure data (0C68). Data gathered by the Marshall Islands Radiological Safety Program related to age at the time of whole-body counting measurements were reviewed. When discrepancies between the three sources of age data became apparent (about April 1982) Medical Program records were assumed correct. Differences, between age groupings reported in Table 1 of the Conard report (Co80) and Tables 24 or 25 as reported here, exist because of the age-at-exposure discrepancies. Two young Rongelap males with severe growth retardation and gradually developed atrophy of the thyroid gland were not included in Tables 24 and 25 because thyroid nodules would not develop in these individuais. Surgical examina~ tion of nodules detected by palpation in the field revealed four persons without nodules at the time of surgery (see Table 24). In addition, two persons too old to undergo surgery were included among those having nodules. B. Tabulation of Risk of Thyroid Cancer The unexposed population incidence rate of thyroid cancer was higher at Rongelap and Utirik than for other sea-level populations, 2 cancers per hundred- thousand person-years observed at Singapore (Le82) versus 59 cancers per hundredthousand person~years observed in the Marshall Islands comparison group. The comparison group makeup has been described previously by Conard (Co80). Thyroidcancer in the United States has been diagnosed at the rate of 2.5 per hundredthousand person-years observed (De75). Our estimated vaiue for thyroid cancer risk from fallout for the exposed population is 150 cancers per million person-gray-years at risk (1.5 cancers per million person-rad-years). This estimate was based on the Marshall Islands’ comparison group incidence, thyroid doses estimated here, and thyroid observations in the exposed groups at Rongelap, Utirik, and Sifo Islands (see Table 25). It could be assumed that the larger studies of cancer gave a more accurate reflection of the spontaneous incidence rate of thyroid cancer at Rongelap and Utirik than the comparison group statistics. For a population of 251 people examined over 29 years, about 0.15 thyroid cancers would be expected on the basis of the rate given at Singapore (Le82). This value when incorporated into the estimate of cancer risk from radiation exposure leads to a Rongelap-Utirik-Sifo population value of 210 thyroid cancers per million person-gray-years at risk (2.1 thyroid cancers per million person-rad-years at risk), 40% higher than the value we estimated using Marshallese comparison statistics. Comparison to Other Estimates of Thyroid Cancer Risk The value for the radiation-induced incidence of thyroid cancer was 147 per million person-gray-years (1.47 cancers per million person-rad~years) for =“ t7 er} 4 - 62 gp oc ot POL - ATS a © , iremmaligipemarems te 2s ee i. Fee C.