125~-14-6535 o ‘ s 6. ~ e nae ewe ee a ee ) oo meee ete eee The high incidence of thyroid nodularity in the irradiated subjects is in agreement with previous data linking irradiation of the gland with subsequent development of thyroid nodules or carcinoma. Since 1311is considered much less tumorigenic for thyroid tumors than x rays, it is rather surprising that, in view of the large contribution of radioiodines to the thyroid ‘dose of the Marshallese, the risk factor (risk/rad) is comparable to that noted following x-ray exposure. This mc be related to the presence of more potent short-lived isotopes of iodine present ia the fallout which accounted for two to three times the dose from 1311. ‘Two boys who developed myxedema received an estimated thyroid dose of 1150 rads. In addition, at least five of the Rongelap population who had appropriate testing prior to surgery had either biochemical hypothyraidism or decreased thyroid reserve. Because of the suspicion of possible hypothyroidism in individuals exposed to even lower calculated doses, a series of studies of thyroid reserve in previously uo operated exposed Marshallese was initiated in 1974. . Since the most sensitive index of inpaired thyroid function is an elevation in serum TSH which occurs through the hypothalmic~pituitary—thyroid feedback axis, serum TSH concentrations and their response to thyrotropin-releasing hormones (TRH) were measured in both the comparison and the exposed Rongelap population. On the basis of these studies, criteria were ‘established for classification of patients as having biochemical evidence of impaired thyroid function~. In a control group of 115 who were not exposed to radiation, 10% had a serum TSH > 3 pU/ml (normal < 3 yU/ml, borderline 3-5 pU/ml, elevated > 5 pU/ml). In 9%, serum TSH was only minimally elevated (4 U/ml or Less). None of these patients had detectable clinical hypothyroidism or thyroid énlergement, but serum T4 concen— trations were generally in the Low:normal range. --- In the exposed Utirik population, 12Z of the subjects tested had at least one basal serum TSH greater than 3 pU/ml, though none of these was in excess of 5 pU/nl. The prevalence of elevated TSH in this population is not significantly different from that of the unexposed group. In the Rongelap and Ailingnae population, 25% of the subjects were found to have at least a single elevated basal serum TSH greater then 3 pU/ml. In two cases, the serum TSH was in excess Of 7 pU/ml. This is a Significantly higher prevalence than in the other two groups pooled. An association of thyroid nodularity and cancer with prior radiation of the thyroid gland, particularly in younger patients, is well—recognized and the asso-— ciation has recently been reviewed by Maxon et al. (Am-J.Med. 63: 967, 1977) and De Groot et al. (Radiation-Associated Thyroid Carcinoma, Grune & Stratton, N.Y., 1977). In addition, it has been recognized that radiation ta the thyroid delivered in the course of treatment of patients with thyroid hyperfunction is associated with hypo- thyroidism in a significant fraction of the patients (as high as 50%) at the higher dose levels. ‘ . There is little data available in the literature relative to the possibility o hypothyroidism following 1311 dosages of less than 2500 rads. Preliminary results of Hanilton and Thompkins (Further Adv.Thy.Res.,k-Fellinger ,R.iofer,Eds.,Vionna 1971,p.60 indicated that eight of 443 subjects (1.8%) diagnostic 1311 tests at less than 16 years. subsequently became hypothyroid after The present studies suggest that there is a significant risk of development of impaired thyroid function many yerrs following estimated thyroid doses of Less than °500 rads from the misture of radiotodines end gamma radtatton present in Fallout foou nuclear denomerions, In the Rangebiup and Ailinenase: ereup, the effect his Cc c e 1 tr C ra ou CEU 18