It seems less likely that this single isolated case among the Utirik people “would involve radiation etiology in view of the low dose received by this group and the fact that no nodular lesions had been noted among the children, ‘Based on the present incidence of thyroid malignancy in the high exposure Rongelap group the risk for development of this malignancy per 10° per person per rad per year is 3 cases for the children exposed at less than 10 years of age, 10 cases for the older people and 5.6 cases for the group ‘as awhole. The risk in the Marshallese children is not inconsistent with that reported by others!3, it has been generally believed that radioiodine exposure was less effective than X-radiation in producing thyroid lesions based primarily on the fact that few thyroid tumors had been noted following radioiodine . . therapy. It seems likely, however, that the scarcity of such findings is related to the high doses of radiation used (5-10, 000 rads or more in the treatment of hyperthyroidism and 50,000 rads or more for ablation of the gland to ameliorate symptoms in certain diseases). Such doses probably are so destructive that they preclude proliferative activity and malignant transformation in. such damaged glands. The increasing incidence of hypothyroidism without tumor formation, years after treatment of hyperthyroid patients with radioiodines illustrates this point. It:has | been shown that tumor formation in animals is not always a dose dependent phenomenon!, Shellabarger et a1,16 showed that breast tumors in rats reached a maximum incidence at about 400 rad and the occurrence of neoplasms fell off with higher doses. Lindsey et a1.8 reported that doses of 1311 in rats in excess of 200-400 pCi were less carcinogenic than lower doses, — . . _. | | i | ~ : ° DOE ARCHIVES . . . /P we Lisa