61 | 16 14} MB Rongelap a Ailingnae {_] Utirik 4 @ Benign q 4 Malignant 10.20 30 40 50 Age at developmentof lesions & & (_"] Unexposed T Figure 47. Relationship of thyroid dose to age whenlesions develop in Marshallese. , Benign: 1, malignant. ceived their dose largely from radioiodines, and the groups receiving x-irradiation. These data are not extensive enoughto show possible threshold effects. Since in animal experiments !31I ts only about “io to is as effective as. x-irradiation in pro- oS bo - Percent lesions oftotal lesions 80 | T Thyroid dose (rads) J Loo ml 10 20 30 40 30 60 Age at developmentoflesions 70 Figure 46. hypothyroidism develops, the cases of thyroid cancer 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 tumorsis in line with this rea- soning. Offsetting, somewhat, the greater incidence of thyroid cancerin childrenis the finding that children survive longer than older people, even with the well differentiated types.13° Thepossible effects of the stress of puberty in the developmentof thyroid lesions have been previously noted.23 The stress of frequent pregnan- cies, which had occurred before the development of malignantlesions in the three Rongelap women, may have been a factor in developmentof neoplasia. Both these correlations, however, may be fortuitous. 2. Comparison of Thyroid Neoplasias From X-Ray Radiation and Radioiodine Irradiation The data in Tables 33 and 34 show thatthe risk per rad for the development of 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, whore- ducing 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 141I (20 to 50 Ci) in the past resulting in thyroid doses up to hundredsof rads, yet only | case with thyroid tumors has been re- ported.!31.132 U.S. Public Health Service workers recently reviewed a large number ofcase histories of people whohad received radioiodines for treatment of hyperthyroidism.!22 They were unable to show any clear-cut increase in incidenceof thyroid tumors in this group compared with a group treated by surgical thyroidectomy. Increasing numbersof the patients treated with !31] 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 therapyfor hyperthyroidism.!!4-116 The numberof cases reported is lower than expected on the basis of dosage to the thyroid. The increased tumorigenesisin the Marshallese mayberelated to the natureof the radiation, more than half the dose being due to short-lived isotopes of iodine (particularly 1421, 1337, and 1357), which are more energetic (see Ap- pendix 9C). Vasilenko and Klassovskiil33 have demonstrated that when these shorter-lived isotopes of iodine are combined with 1411 the tumori-