61 T 30 — TTT im Rongelap 16 _ r T 4 S83 Ailingnae [J Utirik / Varee cust Pe tengats cot teeta besrenzes Cc] Unexposed Thyroid dose (rads) i00 T of 1000 eee T T 1 TTT e Benign 4 Malignant se a ro ! t ' { . 500 { i e 1 e 4&4 @ ! 1 I e a 10 e e » ° ya 8 6-200 30 40 4 ! 50 | OS Age at developmentoflesions Figure 47. Relationship of thyroid dose to age whenlesions develop in Marshallese. e, Benign; a, malignant. 10 =. WSL70 30 40 50 60 Ageat developmentoflesions 8, 12 Figure 46. hypothyroidism develops, the cases of thyroid cancer are fewer than expected.120,121, 128,129 The devel- opment, in the two stunted Marshallese boys, of thyroid atrophy with hypothyroidism but without the development of tumors is in line with this reasoning. Offsetting, somewhat, the greater incidence of thyroid cancerin childrenis the findingthat children survive longer than older people, even with the well differentiated types.15° The possible effects of the stress of puberty in the developmentofthyroid lesions have been previously noted.?3 The stress of frequent pregnan- cies, which had occurred before the development of malignant lesions in the three Rongelap women, mayhave been a factor in development of neoplasia. Both these correlations, however, may be fortuitous. 2. Comparison of Thyroid Neoplasias From X-Ray Radiation and Radiciodine Irradiation The data in Tables 33 and 34 show thatthe risk per rad for the developmentof thyroid neoplasms in the Marshallese was quite similar to that in populations exposed to x-irradiation. The data in Figure 44 indicate a linear relationship between nodularity in the Marshallese children, who re- ceived their dose largely from radiotodines, and the groups receiving x-irradiation. These data are not extensive enoughto show possible threshold effects. Since in animal experiments 1411 is only about Mo to Ks 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 havereceived diagnostic 1411 (20 to 50 pCi) in the past resulting in thyroid doses up to hundredsof rads, yet only 1 case with thyroid tumors has been reported.131.132 U.S. Public Health Service workers recently reviewed a large numberofcase histories of people who had received radioiodines for treatment of hyperthyroidism.!22 They were unable to show anyclear-cut increase in incidenceof thyroid tumors in this group compared with a group treated by surgical thyroidectomy. Increasing numbers of the patients treated with 431] developed varying degrees of hypothyroidism in later years. The low incidence of tumors following such treatment may be related to the high doses of radiation given to the thyroid,sufficient to 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.?14-146 The numberof cases reported is lower than expected on the basis ofdosage to the thyroid. The increased tumorigenesis in the Marshallese maybe related to the natureof the radiation, more thanhalf the dose being due to short-lived isotopes of iodine (particularly 1971, 133, and 135]), which are more energetic (see Ap- pendix 9C). Vasilenko and Klassovskii!5? have demonstrated that when these shorter-lived isotopes of iodine are combined with 151] the tumori-