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 ibnormalities seen, since 200 natives of the same ethnicbackground 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 goitro- genic 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 yreater 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 averayge 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 may 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 Nayasaki exposed to radiation from the atomic-bomb explosions. The numbers are small, however, com- The treatmentof the exposed group with levothyroxine deserves some further comment. Bielschow- sky*® 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 and unpublished data by Godwin™® demonstrating a reduced incidence of [!-induced adenomas in rats treated with thyroid hormone. This form oftreatment, 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 Ronye- lap Island who were accidentally exposed to radioactive fallout in 1954. Definite thyroid nodules were noted in 1] 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 almost 15,000 individuals, as compared to 2 cases in slightly less than 5000 unexposed individuals.* _ skin from fallout products and internal absorption of fission products. One case with a nodule was noted These people were exposed to varying doses ‘of in an adult woman in the smaller Ronyelap ygroup external radiation to the thyroid gland but not to (16 of the 18 are still alive) that had received less internal exposure from radioiodine. than half the exposure of the other group. In 200 The growth retardation previously noted in some individuals of a control proup not exposed no such of the exposed children has been assumed to be thyroid abnormalities were found. In the more due to the radiation, but the mechanism has not i teresting that the exposedyirls have shown verylittle retardation of growth and development although the nodules are more prevalent among them. Except for the 2 boys with hypothyroidism, the rest of the chil- heavily exposed group, thyroid abnormalities de- veloped in 55 per cent of children exposed at less than ten years of age. Five children were found at surgery to have benign adenomatous goiters. The 1 adult patient had a mixed papillary and follicular carcinoma, with localized metastasis. Two boys showed marked retardation of prowth, apparently owing to primary hypothyroidism. dren with growth retardation have shown normal pro- . The radiation etiology in these cases appears to be reasonably certain in view of the following facts: enough to account for the growthretardation seen. The finding of high TSH levels in the 2 most retarded boys radiation (adults about 300 rads, and children about 700 to 1400 rads); and the incidence of thyroid ab- tein-bound iodine and cholesterol values. Minimal hypothyroidism may have been missed and may be 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. 5012902 the thyroid glands received a substantial dose of radiation from radioiodines and external gamma normalities was high in the exposed group and ab- sent in an unexposed control population living on the same island. The present findings suggest that the seriousness of the internal hazard associated with fallout, particularly from radioiodine, must be revised upward. PRIVACY ACT MATERIAL REMOVED ee been known.? With the recent development of frank hypothyroidism in 2 of the most retarded boys in the exposed yvroup hypothyroidism seems the most likely cause. In 2 other retarded boys ( and ) thyroid nodules have developed. However, it is in- eeie ee eee eee AUNMattes ot ag Rte 0+e RRATTI prising 19 cases in a combined exposed yroup of