8 lltea Te ek ne da eee ae ee ee = eee va sme TE ey PATHOLOGICAL EFFECTS OF THYROID IRRADIATION 7 INTRODUCTION The constituent groups of the National Academy of Sciences - National Research Council Committees on the Biological Effects of Atomic Radiation, - now disbanded, had met periodically since their formation in 1955 to consider various aspects of the general problem, In 1961 a report on Internal Radioactive Emitters+ was issued, which included a discussion of the effects of iodine-131 on the human thyroid gland. A special report on the Pathological Effects of Thyroid Irradiation was issued by the Federal Radiation Council in July, 1962.2 Enough new evidence on the effects of irradiation of the thyroid has come to hand to warrant consideration by the Advisory Committee to the Federal Radiation Council; for this purpose there was established a Subcommittee on the Effects of Radiation on the Thyroid Gland augmented by consultants with special knowledge of the field. Although parts of the available data are wnpublished and incomplete, some investigations have reached a point where certain conclusions can be safely drawn. Some of these data come from long-term studies on the effects of medi- cally indicated irradiations involving the thyroid gland of man. Other data come from long-term animal experdments using either iodine-131 or X-rays as the source of radiation. The human thyroid gland may be exposed to radiation from a variety of sources, Medical and dental requirements can lead to an X-ray exposure, either from a direct beam or as scatter from the irradiation of adjacent areas. Radioactive iodine may be administered for either diagnostic or therapeutic purposes. Substantial quantities of iodine-131 are produced in nuclear fission and may be released to the environment, principally during nuclear testing in the atmosphere or from some types of reactor accidents. The most important radionuclide of iodine, iodine-131, has a very short half-life of 8 days which limits the quantities that can gain entrance into the body. Fallout from nuclear detonations or from a nuclear reactor accident may deposit iodine-131, as well as other radionuclides, including very short-lived radioiodines, on vegetation and in water supplies downwind from the point of release, The absorption of idodine-131 by inhalation will be unimportant except possibly in fallout intensities which are intolerable for other reasons or immediately following a reactor accident. Direct absorption through the skin has not been demonstrated to be an loublication No. 883, "Internal Emitters," 1961, of the National Academy of Sciences-National Research Council. 2 pathological Effects of Thyroid Irradiation," Federal Radiation Council, . Washington, D. C., July 1962. SOE ARCHIVES