Radiation exposure to family members of patients with thyrotoxicosis treated with iodine-131

Purpose The purpose of this study was twofold: (1) to measure the radiation exposure to family members of out-patients with thyrotoxicosis treated with radioiodine, ¹³¹I, using the recommendations from the European Commission (EC) guidance and age-specific periods for behaviour restrictions; (2) to use the results to identify necessary restrictions to ensure recommended dose constraints.Methods The study population comprised 76 family members (46 adults and 30 children below the age of 18) of 42 patients. The patients were treated with an average activity of 417 MBq (range 260–600 MBq). They received oral and written EC recommendations about behaviour restrictions (translated into Norwegian). On the day of treatment we repeated the oral instructions to the patient and an adult family member. The time periods for restrictions were 14 days for children aged 0–10 years, 7 days for persons aged 11–59 years and 3 days for persons aged 60 years and older. Family members wore a thermoluminescent dosimeter (TLD) on each wrist day and night for 2 weeks. The doses received were adjusted to give an estimate of the expected values if the TLDs had been worn indefinitely.Results Radiation doses well below the recommended dose constraints were measured for all adult family members and children, except one 2-year-old child; in the latter case the mother probably did not comply with the instructions given.Conclusion The radiation dose to family members of thyrotoxic patients treated with up to 600 MBq of radioiodine is well below recommended dose constraints if EC instructions are given and compliance is adequate. The duration of restrictions for various age groups used in this study may be considered when establishing guidelines in Norway.