LATE EFFECTS OF RADIOACTIVE IODINE IN FALLOUT of such TSH suppression to prevent the development of thyroid carcinoma has been shown experimentally in rats (30). The one carcinoma in the Marshallese adult is quite different from the type of disease about which we have thus far been concerned, since there was no hyperplasia of the surrounding thyroid gland. This was typical, then, of the usual case of thyroid 4, carcinoma occurring in a nonirradiated population. On the other hand, there is considerable evidence that thyroid carcinoma in young adults, and especially in children, is frequently caused by radiation of the cervical area in childhood. Lindsay and Chaikoff (20) have reviewed the vari- ous clinical reports on this subject, and Winship and Rosvoll (31) reported that as many as 80% of children with thyroid car- cinoma, in a series of 562 cases, have a history of prior cervical irradiation. The amount of radiation, which is usually given in the form of X-ray therapy for thymic hypertrophy or tonsillitis, can be even smaller than that in the Marshallese population, being in the range of 90 to 1,300 rads. This was the dose range in a prospec- I239 plasms in a significant number of exposed individuals. It would also seem likely that lesser amounts of radiation, every direct hit on a gene being effective, might also lead to cancer formation. This, however, be- comes a problem in disease statistics and is one that is currently engaging the inter- est of many, thus far with no clear-cut answers. The experience in the Marshall Islands has, at least, served to illuminate one portion of the spectrum of thyroid radiation effects in man. I would nowlike to call for questions. Dr. WoLFF: What fraction of the radiation was from 121]? Dr. Conarp: Probably less than half. Dr. WotFrF: In connection with that, was there any '*°]? Have you gotten any counts on the material that was removed surgically? Dr. RALL: 2*°] has a half-life of approximately 17 million years, so that essentially it is unradioactive. For any such molecules in the lifetime we are talking about, they do not decay but arestill there to be mea- sured by neutron activation. The question thyroid carcinoma developed, on the av- is, would there be any there? Well, we do not know. Maybe we should have measured it. Maybe there is still tissue left. I of persons exposed to such radiation (20, over in the affected individuals would leave tive study of over 4,500 patients in whom erage, 11 years later in approximately 0.5% 32, 33). Although adults may not be immune to radiation-induced tumors—as suggested by the apparent increased prevalence of thyroid cancer in adults exposed to the atomic bomb in Hiroshima (34) and other types of radiation (35, 36)—the propensity for this sequela in children is almost surely related to the fact that in the cells of the growing thyroid gland there must be numerous mitoses, whereas mitoses in the adult gland are rare. The gene alterations leading to cancer formation pre- sumably require cell division for their expression. It appears clear that the sizable amounts of irradiation that we have been discussing have the potential to produce thyroid neo- am afraid that 10 years of biological turn- almost none of the original iodine around for measurement. Dr. JessE Roto: With hyperthyroid patients who have been treated with radio- iodine it is common to see a defect where. the early uptake of iodine is high, but then a large portion of this iodine is not organified. I was curious as to why it did not seem to show upin these radiated groups. Dr. Rossins: I have no real answer. There is a difference in the radiation delivered: The hyperthyroid patients get about 10,000 rads, and these children got about 1,000 rads. Also, these were children who did not have so much damage that they could not grow nodular goiters. The hyperthyroid patients are probably dam- PRPiaaaeTe Volume 66, No. 6 June 1967