Cancer risk following radioactive iodine-131 exposures in medicine

Most types of cancer have been associated with external radiotherapy and exposures from the atomic bombs in Hiroshima and Nagasaki. Although epidemiologic, and some experimental studies, suggest that iodine-131 (I-131) may be less effective in inducing malignancies, the potential late health effects of I-131 remain a concern to both the general public and the medical community. Other radionuclides are currently used for diagnosis, but it is estimated that over 10 million adults have had I-131 treatment of choice for hyperthyroidism and is used frequently to treat thyroid cancer. Since 1942, when I-131 therapy for hyperthyroidism was introduced, millions of patients, almost all adults, have had this treatment. In contrast to the substantial medical use of iodine-131 in adults, its use in children and adolescents has been extremely limited because of concerns regarding its long-term carcinogenic and genetic effects. Some physicians, however, are advising re-evaluation of treatment for children because it is convenient, effective and relatively inexpensive. Over the last few decades, case reports and some small epidemiologic studies have linked medical exposure to I-131 with thyroid cancer and leukemia. Attention also has focused on breast cancer and cancers occuring in organs that concentrate appreciable quantities of iodine, i.e. salivary glands, stomach, kidney, and bladder. In this report, the author briefly summarizes the major epidemiologic studies of medical exposures to I-131 and compares the results with what is known about external radiation exposure