PRIVACY ACT MATERIAL REMOVED ceived thyroid irradiation in 1954 seems to conform in a general way to, the concepts outlined above. Radiation appears to have been the cause of the thyroid abnormalities seen, since 200 natives of the same ethnic background and living under identical conditions showed no thyroid disease. Furthermore, there is no evidence that these people have been exposed to other factors that might cause pathologic changes in the gland: urinalyses indicate that the iodine intake is adequate, and no dietary goitrogenic factors have been implicated. In addition, the data in the present study show a much greater incidence of thyroid disease in children than in adults in accord with the findings cited above. This greater sensitivity of infants may also be related to the relative magnitudes of the dose of radiation received, the infant gland probably receiving five to ten times the radiation dose that an average adult’s gland received. The dose range of from 700 to 1400 rads delivered to the children’s thyroid glands is similar to the doses received during thymic irradiation. The apparently greater incidence of pathologic changes in the glands of the Marshallese is not clear. It mav be related to a greater dose of radiation received by the Marshallese since the calculations for thyroid dose in these people is subject, as noted above, to large uncertainties. There appears to be an increased incidence of thyroid carcinoma in inhabitants of Hiroshima and Nagasaki exposed to radiation from the atomic-bomb explosions. The numbers are small, however, com- prising 19 cases in a combined exposed group of almost 15,000 individuals, as compared to 2 cases in slightly less than 5000 unexposed individuals.* These people were exposed to varying doses of external radiation to the thyroid gland but not to internal exposure from radioiodine. The growth retardation previously noted in some of the exposed children has been assumed to be due to the radiation, but the mechanism has not been known. With the recent development of frank hypothyroidism in 2 of the most retarded boys in the exposed group hypothyroidism seems the most likely cause. In 2 otherretarded boys. and thyroid nodules have developed. However,it is interesting that the exposed girls have shownverylittle retardation of growth and development although the nodules are more prevalent among them. Except for the 2 boys with hypothyroidism, the rest of the children with growth retardation have shown normal protein-bound iodine and cholesterol values. Minimal hypothyroidism may have been missed and may be enoughto account for the growth retardation seen. The finding of high TSH levels in the 2 most retarded boys with hypothyroidism and slight elevation in 2 other retarded children strongly indicates primary hypothyroidism. The growth response of these children after thyroid feeding will offer an interesting therapeutic test of the hypothyroid etiology of the growth retardation: The treatment of the exposed group with levothyroxine deserves some further comment. Bielschowsky?# and Astwood and Cassidy* have reviewed the favorable effects of thyroid treatment of patients with nodules of the thyroid gland. The only experimental evidence found directly applicable to the Marshallese situation is a paper by Nichols et al. and unpublished data by Godwin®* demonstrating a reduced incidence of I'!-induced adenomas in rats treated with thyroid hormone. This form of treatment, therefore, seems reasonable in the Marshallese. ' The implications of the present findings are twofold. In the first place, contrary to previous concepts, the. quantity of radioisotopes of iodine in fallout of the close-in type associated with atomicbomb detonations must be regarded as a major longterm hazard. Secondly, the development of hypothyroidism, of thyroid adenomatoid lesions and of a thyroid carcinoma after doses of radioiodine that deliver 300 to 1400 rads to the gland makes caution in the use of radioiodine necessary SUMMARY AND CONCLUSIONS Pathologic changes in the thyroid gland were found in a number of Marshallese people of Rongelap Iskand who were accidentally exposed to radio- active fallout in 1954. Definite thyroid nodules were noted in 11 people, minimal changes in 5 others, and hypothyroidism in 2. All but 1 case occurred in the more heavily exposed population (55 living of the original 64 persons), who received about 175 rads of whole-body gamma radiation, burns of the skin from fallout products and internal absorption of fission products. One case with a nodule was noted in an adult woman in the smaller Rongelap group (16 of the 18 are still alive) that had received less than half the exposure of the other group. In 200 individuals of a control group not exposed no such thyroid abnormalities were found. In the more heavily exposed group, thyroid abnormalities de- veloped in 55 per cent of children exposed at less than ten vears of age. Five children were found at surgerv to have benign adenomatous yoiters. The 1 adult patient had a mixed papillary and follicular carcinoma, with localized metastasis. Two boys showed marked retardation of growth, apparently owing to primary hypothvroidism. The radiation etiology in these cases appears to be reasonably certain in view of the following facts: the thyroid glands received a substantial dose of radiation from radioiodines and external gamma radiation (adults about 300 rads, and children about 700 to 1400 rads); and the incidence of thyroid abnormalities was high in the exposed group and ab- sent in an unexposed control population living on the same island. The present findings suygvest that the seriousness of the internal hazard associated with fallout, particularly from radioiodine, must be revised upward. PRIVACY ACT MATERIAL REMOVED