Thyroid cancer after diagnostic administration of iodine-131 in childhood

To determine the carcinogenic effects of diagnostic amounts of I-131 on the juvenile thyroid gland, a multicenter retrospective cohort study was condu cted on 4,973 subjects who either had been referred for diagnostic tests us ing uptake of I-131 (n 2,262) or had had a diagnostic procedure on the thyr oid without I-131 (n = 2,711) before the age of 18 years, Follow-up examina tions were conducted after a mean period of 20 years after the first examin ation in 35% of the exposed subjects (n = 789) and in 41% of the nonexposed subjects (n = 1,118), Iodine-131 dosimetry of the thyroid was carried out according to ICRP Report No 53, and the median thyroid dose was 1.0 Gy, In the exposed group, two thyroid cancers were found during 16,500 person-year s, compared to three cancers in the nonexposed group during 21,000 person-y ears, The relative risk for the exposed group was 0.86 (95% CI: 0.14-5.13), The study did not demonstrate an increased risk for thyroid cancer after a dministration of I-131 in childhood. (C) 2001 by Radiation Research Society .