St nllTN oe a me ete ae ee a Pn s or Lae soem eT PATHOLOGICAL EFFECTS OF THYROID IRRADIATION 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 19495 to consider various aspects of the general problem, In 1961 a reportJon Intermal Radioactive Emitters! was issued, which included a discussion of the effects of iodine-131 on the human thyroid gland. A special report on Council in July, 1962.2 Enough new evidence on the effects of of the thyroid has come to hand to warrant consideration by the Committee to the Federal Radiation Council; for this purpose thdre was established a Subcommittee on the Effects of Radiation on the T augmented by consultants with special knowledge of the field. parts of the available data are wnpublished and incomplete, som investigations have reached a point where certain conclusions can be saf ly drawn. Some of these data come from long-term studies on the effedts of medi- cally indicated irradiations involving the thyroid gland of mand Other data come from long-term animal experiments using either iodine-131 or X-rays as the source of radiation, The human thyroid gland may be exposed to radiation from a Wwariety 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 fbdjacent areas, Radioactive iodine may be administered for either diagnostic or therapeutic purposes. Substantial quantities of iodine-131 are Broduced in nuclear fission and may be released to the environment, principally during nuclear testing in the atmosphere or from some types of actor accidents. The most important radionuclide of iodine, iodine-131, has very short half-life of 8 days which limits the quantities that can gain en rance into the body. Fallout from nuclear detonations or from a nuclear re ctor accident may deposit iodine-131, as well as other radionuclides, inc short-lived radioiodines, on vegetation and in water supplies d from the point of release, The absorption of idodine-131 by inh will be unimportant except possibly in fallout intensities which tolerable for other reasons or immediately following a reactor a Direct absorption through the skin has not been demonstrated to lp ublication No. 883, "Intermal Emitters," 1961, of the National]Academy of Sciences-National Research Council. 2"pathological Effects of Thyroid Irradiation," Federal Radiatiog _ Washington, D. C., July 1962. DOE ARCHIVES Council,