tae ~.- een ok eee ae, Ss et * ee. ow ere we, ene 3 -5- oe cervical spine, or larynx and fluoroscopy of the larynx or esophagus, the thyroid gland may be exposed to a fraction of a roentgen up to several roentgens. These are frequent procedures, and to date no examples of cancer of the thyroid have been attributed to such exposures, However, systematic effort to determine such a relationship has not been made to our knowledge. b. Therapeutic X-ray In radiation treatment of hyperthyroidism, the thyroid gland may be exposed to doses of several thousand roentgens. This procedure has been carried out on thousands of patients, and carcinoma of the thyroid is an extremely rare complication. Another practice, no longer in common use, is to treat supposedly enlarged thymus glands in infants and children by exposing the upper chest and neck to doses of 100 r to 600 r or more of X-ray. When large treatment ports, particularly those placed posteriorly, were used, the thyroid gland often received the full depth dose from the primary X-ray beam. Similar exposures of the thyroid may result from X-ray treatment of enlarged cervical lymph nodes or skin diseases. Subsequent studies of these patients, both retrospective and prospective, by several authors, have disclosed a small but significant incidence of thyroid cancer in excess of the expected rate as determined by comparison with control groups of siblings. This indicates that the thyroid gland in children is susceptible to cancer induction by radiation at relatively high doses. Evidence at low doses is incomplete. 5. Exposure to Jodine-131 a. Diagnostic Procedures The use of iodine-131 was introduced into clinical medicine about 25 years ago, and for 15 years it has been widely used in a variety of diagnostic procedures. Most of these diagnostic procedures utilize between 5 to 100 microcuries of iodine-131, and most of the retained dose concentrates in the thyroid. No cases of thyroid cancer induction have been reported in the patients who have undergone these procedures. b. Therapeutic Procedures The principal uses of iodine-131 are in the treatment of hyper- yy ae thyroidism and in the management of some cases of thyroid cancer. The latter cases must beeximeed from present consideration since the radiations were acting on tissues already cancerous. There is little evidence at hand that any of the treatments for hyperthyroidism has produced a thyroid cancer, although doses have ranged from a few thousand rads upward. Ablative doses would in effect rule out the possibility of tumor induction. Sctaffurth, J. $&.: Thyroid Cancer After 131-I Therapy for Thyrotoxicosis. ‘Brit. J.° Radiol.39:471-473, 1966 JDOE ARCHIVES