38 not very reliable. From our surveysof the unexposed people of Rongelap and Likiep (a nearby atoll not exposed to fallout), the incidence appears to be about 3%, mostly present in oider age groups (see Figure 29 and Table 25). We have seen a few cases of hyperthyroidism and myxedema at the Majuro Hospital, but no statistics are available. Two cases of thyroid cancer are reported from hospital admissions for a 10-year period (19521962) for the Marshall Islands, the population varying between 15,000 and 20,000 during that period. This has been estimated by Trust Terri- tory medical personnel to be about half the actual number of cases (therefore 8 cases per 20,000 people per 20 years was used for statistical com- parisons). Data on iodine intake and excretion in the Marshallese (tabulated below and presented in detail in Appendix 9) indicate that iodine-deficiency goiter would not be expected in this population. Sample . 28 Urines (1965) 19 Urines (1974)* 7 Diets 1974)" Iodine, av. pg/day (range) 105 (19-279) 127 (25-266) 70 (48~152) The urinary iodine excretionis somewhatlower than the U.S. mean of 190 pe/day (18-483) in 1941.9 On the basis of the few diets analyzed, the daily iodine intake seems to be within the recommended range of50 to 75 yg.95 These iodine levels are somewhatlower than would be expected in an oceanic population but are much higherthan seen in areas of endemic goiter.96 The Marshallese diet contains no know goitrogens, and diffuse goiters (typical of endemic goiter) have not been observed. The high incidence of both benign and malignant thyroid nodules in the exposed Rongelap people appears to be clearly related to radiation exposure with a large component due to radio- iodine in the faliout. Numerous studies on animals have shownthat thyroid neoplasia follows expo- sure both to x-irradiation and to radiciodines.?7-99 Such tumors maybe benign or malignant and appear to be dose-dependent to some degree. The incidenceof thyroid tumors is increased in Japanese atom bomb survivors!}00-103 (Figure 43). There is a considerable amountof data showing that children who were given radiation to the head and neck region for treatment of thymic hyper- *The iodine analyses were done by M.T. Kinsley and D.F. ~An S0Gbf309 = 30 = 3 OF (2 Hiroshima Nagasaki = 30t a Y a 27 lor Notincity 0-9 10-99 T65 dose 100 + rad Figure 43. Prevalence of diseases of the thyroid,fifth examination cycle, by radiation dose and city for females age 0 to 19 at time of bomb. (From Belsky et-al.104} trophy, acne, and fungus of the scalp have an in- creased incidence of both benign and malignant thyroid lesions in later years.!®5-112 Reports of tumorigenic effects of radioiodine in man are more limited. Shelineet al.,‘!5 in their follow-up study of 250 patients treated for hyperthyroidism,reported 8 having nodular goiter, of whom 6 had been irradiated at age <20 and 4 at age <10. More recentiy a numberof cancers of the thyroid have been reported in patients previously treated with radioiodine for hyperthyroidism.!14-!16 The number of such cases reported is, however, lower than might be expected on the basis of the widespread use of 1511, perhaps because thecells are more likely to undergo lethal damage.117-122 In the more heavily exposed Rongelap group the adult thyroids received a dose (335 rads) about twice that to the whole body and those of small children (700 to 1400 rads) about 8 timesthat to the whole body. Onthebasis of the incidence of benign nodules in the unexposed Marshal Islands populations examined, about 3 to 4 cases would be expected during the 20 years in the Rongelap exposed group, whereas 24 occurred. In the Utirik group about6 would be expected, and 6 occurred. Regarding cancer of the thyroid, on the basis of MarshailIslands statistics, about 0.033 cases would be expected in the Rongelap group over the 20- year period, whereas 3 occurred. In the Utink population about 0.06 cases would be expected, and 1 occurred; in view of the low dose of radiation it is unlikely that this case is radiation induced. Tables 33 and 34 show the incidence and the risk per rad in the Marshallese compared with that in other populations for both benign and malignant thyroid neoplasms. Data on benignthy- roid nodularity are scarce, but the incidence in