ee mo me a te Ue + ite “7 re - -6From this and other evidence, it appears that iodine-13] is|consid-~ erably less effective than comparable doses of externally applied X-rays in producing thyroid cancer. The magnitude of this difference cd4nnot be stated since not-a single confirmed case ascribable to iodine-13] is known. In making a comparison it must be kept in mind that X-rays are ofdinarily delivered at a high dose rate in a single sitting or in a few divided doses; and the thyroid as well as the blood vessels supplying it and thq adjoining tissues are wmiformly exposed, In addition the age of the patierts treated and their clinical conditions are rarely the same in the two typds of treat- ment, If the radiation were administered at the same low dose rdte for both iodine-131 and X-ray, the ostensible difference might not be as 6. great. Reactor Accident In a reactor accident, radioactive iodine was released to the environment! , and control measures were instituted to prevent human thyzpid doses from exceeding 20 rads. No increase in the incidence of thyroid freoplasia in this area has been reported, but it must be remembered that the complete effects of this episode will not be known for many years. 7. Total Radiation Doses in Childhood Cancer of the Thyroid Although thyroid cancer occurs in children who are not knownjto have been exposed to artificially produced radiation, some history of K-ray ex- posure has been obtained by several workers in well over half the] cases in which careful inquiry has been made. The X-ray doses received|by most of these subjects are difficult to determine, but by tracing the fecords of radiologists it appears that the smallest doses associated with subsequent cancer range from about 100 r measured in air upwards. Only a very small number at these low levels have been reported. 8. / Thyroid Abnormalities in a Marshallese Population Exposed to Radioactive Fallout The development of thyroid nodules and hypothyroidism has begn noted in a number of Marshallese people of Rongelap Is}and in the Pacific who had been exposed to radioactive fallout in 1954.9 This developmegt is believed to be a late effect of irradiation of the thyroid gland grom intermal absorption of radioiodines and from external gamma radiafion at the time of the fallout. A total of 64 Rongelap people (54 living in 1966) received a whole body dose of gamma radiation of 175 rads, qxtensive direct irradiation of the skin from deposition of fallout thereon fand in- ternal absorption of radionuclides in the fallout. Eighteen othe Rongelap people (14 living in 1966) received a lesser exposure of Jabout 70 rads of gamma radiation along with a smaller dose to the skin and internal absorption of less amounts of radioelements. A total of [157 individuals on the island of Utirik received a whole body gamma ddse of approximately 14 rads. %conard, R. A., Rall, J. E., and Sutow, W. W.: Thyroid Nodules aq a Late Sequela of Radioactive Fallout. New England J. Med. 274:1392-1399, 6/23/66. POE ARCHIVES