Production and Clinical Development of a New Ideal Radioisotope of Iodine — Iodine-123

Abstract

The use of radioiodine for thyroid tests still comprises some 57 % of the proce-dures performed in Nuclear Medicine Laboratories according to the recent Stanford Research Institute Survey conducted by the Bureau for Radiological Health [1]. Wide diagnostic use of Iodine-131 for thyroid tests results in what has been considered a tolerable absorbed radiation dose to the thyroid. Certainly there has been no direct study indicating a significant deleterious effect from Iodine-131 in such use and probabilities are against any study ever conclusively demonstrating measurable permanent radiation effects. However, a recent review by Hempleman has raised the possibility that adenomas are induced by as little as a 20 rad dose of external radiation to the thyroid of young individuals [2]. As an approximate figure, an adult with a normal uptake and gland and a 100 μCi administered dose of Iodine-131 might be expected to receive 150 rad to the thyroid. Younger individuals would, of course, receive relatively larger doses because of smaller glands, but similar uptake values. Absorbed doses associated with scanning procedures with Iodine-131 then may approach the levels questioned by Hempleman as inducing adenomas. Thus, only marginal evidence would prompt one to suspect the diagnostic use of Iodine-131 as having permanent deleterious radiation effects on the thyroid, except perhaps in children. Certainly, at this time, a dose reduction motive alone would probably not warrant abandoning the convenience and economics of Iodine-131.