Incidence of malignant thyroid tumors in humans after exposure to diagnostic doses of iodine-131. II. Estimation of thyroid gland size, thyroid radiation dose, and predicted versus observed number of malignant thyroid tumors.

The size of the thyroid glands was analyzed for 10% of the patients in a selected group that had been exposed to diagnostic doses of 131I. The mean thyroid gland weight +/- SD was 50 +/- 33 g for patients 20 or more years of age and 10 +/- 5 g for patients less than 20 years of age. With the present follow-up, diagnostic doses of 131I appeared not to be associated with an increased risk for later development of malignant thyroid tumors. Possible reasons for the difference between the observed number of such tumors and the number expected (47-124) on the basis of risk estimates of the United Nations Scientific Committee on the Effects of Atomic Radiation are discussed.