61 eo 7 rT ! 30+ 1 Tal Rongeiap 4 [_] Utirik 4 SS Ailingnae ([_] Unexposed . | 1000 4 of qT 2m vee . 300 ty T e Benign : 4 Malignant . | ty i | ! - 1 | 17 e & I @ . | * e » . | 0 10 ry 820 ©6930 4 «©6530 6S Age at developmentoflesions 5 60 a rr:is is i Figure 47. Relationship of thyroid dose to age whenlesions develop in Marshallese. @, Benign; a, malignanc. i o Percent lesions of total iesions yg yp Phyruid duse (rads) T 12 \ ceived their dose largely from radioiodines, and the groups receiving x-irradiation. These data are not extensive enough to show possible threshold effects. Since in animal experiments /3!1 is only 30 a 40-50 Age at developmentoflesions Figure 46. hypothyroidism develops, the cases of thyroid can- cer are fewer than expected. 120,121, 128,129 The development, in the two stunted Marshallese boys, of thyroid atrophy with hypothyroidism but without the developmentof tumors is in line with this reasoning. Offsetting, somewhat, the greater incidence of thyroid cancerin childrenis the finding that chil- about Mo to \s as effective as x-irradiation in producing thyroid tumors,85.120.129.130 why do the Marshallese data indicate near equality of effect? It is estimated that thousands of children have received diagnostic 1311 (20 to 50 #Ci) in the pastresulting in thyroid doses up to hundreds ofrads, yet only | case with thyroid tumors has been reported.131.132 U.S. Public Health Service workers recently reviewed a large numberof case histories of people who had received radioiodines for treatment of hyperthyroidism.!22 They were unable to show any clear-cut increase in incidence of thyroid tumors in this group compared with a group treated by surgical thyroidectomy. Increasing dren survive longer than older people, even with numbers of the patients treated with 1311 devel- the developmentof thyroid lesions have been pre- years. The low incidence of tumors following such treatment may be related to the high doses of the well differentiated types. 15? The possible effects of the stress of puberty in viously noted.25 Thestress of frequent pregnan- cies, which had occurred before the development of malignantlesions in the three Rongelap women, may have beena factor in developmentof neoplasia. Both these correlations, however, may be fortuitous, 2. Comparison of Thyroid Neoplasias From X-Ray Radiation and Radioiodine Irradiation oped varying degrees of hypothyroidism in later radiation given to the thyroid, sufficientto destroy its regenerative capacity. It should be noted, however, that in the past few years a numberof thyroid malignancies have been reported following radioiodine therapy for hyperthyroidism.!14116 The number of cases reported is lower than expected on the basis of dosage to the thyroid. The increased tumorigenesis in the Marshallese mayberelated to the natureof the Thedata in Tables 33 and 34 show thatthe risk per rad for the developmentof thyroid neoplasms in the Marshallese was quite similar to that in radiation, more than half the dose being due to short-lived isotopes of iodine (particularly 151, Figure 44 indicate a linear relationship between demonstrated that when these shorter-lived iso- 133], and 135]), which are more energetic (see Ap- populations exposed to x-irradiation. The data in pendix 9C). Vasilenko and Klassovskii!33 have nodularity in the Marshallese children, who re- topes of iodine are combined with 131 the tumori- 690Gb 158