Radiation safety considerations for post-iodine-131 hyperthyroid therapy

The purpose of this study was to develop guidelines based on patient measurements as to when iodine-131- (131I) treated hyperthyroid patients may resume close personal contact. External exposure rates were measured on 59 patients using an ionization survey meter in the upright position. The initial measurement was recorded within 20 min post-dose administration at one meter. Exposure rates were measured 2-11 days post-dose administration at 1, 0.6, and 0.3 meters from the patient's thyroid. In the administered dose range of 3 to less than 12 mCi of 131I, all 40 patients measured less than or equal to 2.0 mR/hr at one meter on Day 0, and 25 patients (25/29) were less than or equal to 2.0 mR/hr at 0.6 meter on Days 2-4. Guidelines can be prepared based on the administered dose that are rational and in conformity with existing radiologic health standards.