T T 1 5 | - cal | | wa Rongelap 16 _ do te Ld B0e _d Aulingnae (_] Ctirik Percent lesions of tutal lesions (* Unexposed q ‘Thyroid dose (rads) 1906 1000 T @ t oe T T e Benign oe pe 300 rT] \ 1 ' ! & - T 1 1 ' | e | \ | O14 10 20.30 i50—«i 8S Age at developmentof lesions Figure 47. Relationship of thvroid dose to age whenlesions develop in Marshallese. @, Benign: =, malignant. 10 20 30 40 30 60 Age at development of lesions 70 80 Figure 46. hvpothyroidism develops, the cases of thyroid cancer are fewer than expected. !20.121.128,129 The devel- opment, in the two stunted Marshallese boys, of thyroid atrophy with hypothyroidism but without the developmentof tumorsis in line with this reasoning. Offsetting, somewhat, the greater incidence of thyroid cancer in childrenis the findingthatchildren survive longer than older people, even with the well differentiated types. !3° Thepossible effects of the stress of puberty in the developmentof thyroid lesions have been previously noted.23 Thestress of frequent pregnancies, which had occurred before the development of malignantlesions in the three Rongelap women, may have beena factor in development of 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 thattherisk 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 radioiodines, and the groups receiving x-irradiation. These data are not extensive enoughto show possible threshold effects. Since in animal experiments !3!1 is only about ‘io to 5 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 ofchildren have received diagnostic !31I (20 to 50 Ci) in the past re- sulting in thyroid doses up to hundredsofrads, 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.122 They were unable to show anyclear-cut increase in incidenceof thyroid tumors in this group compared with a group treated by surgical thyroidectomy. Increasing numbersof the patients treated with }31I 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 hvperthyroidism.1!4-116 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 nature ofthe radiation, more than half the dose being due to short-lived isotopes of iodine (particularly +371, 133], and 1351), which are more energetic (see Ap- pendix 9C). Vasilenko and Klassovskiil33 have demonstrated that when these shorter-lived isotopes of iodine are combined with 14!I the tumori-