Radiation exposure of the families of outpatients treated with radioiodine(iodine-131) for hyperthyroidism

Patients who receive radioiodine (iodine-131) treatment for hyperthyroidism (195-800 MBq) emit radiation and represent a potential hazard to other ind ividuals. Critical groups amongst the public are fellow travellers on the p atient's journey home from hospital and members of the patient's family, pa rticularly young children. The dose which members of the public are allowed to receive as a result of a patient's treatment has been reduced in Europe following recently revised recommendations from ICRP. The annual public do se limit is 1 mSv, though adult members of the patient's family are allowed to receive higher doses, with the proviso that a limit of 5 mSv should not be exceeded over 5 years. Unless the doses received during out-patient adm inistration of radioiodine can be demonstrated to comply with these new lim its, hospitalisation of patients will be necessary. The radiation doses rec eived by family members (35 adults and 87 children) of patients created wit h radioiodine at five UK hospitals were measured using thermoluminescent do simeters mounted in wrist bands. Families were given advice (according to c urrent practice) from their treatment centre about limiting close contact w ith the patient for a period of time after treatment. Doses measured over 3 -6 weeks were adjusted to give an estimate of values which might have been expected if the dosimeters had been worn indefinitely. Thirty-five passenge rs accompanying patients home after treatment also recorded the dose receiv ed during the journey using electronic (digital) personal dosimeters. For t he "adjusted" doses to infinity, 97% of adults complied with a 5-mSv dose l imit (range:0.2-5.8 mSv) and 89% of children with a 1-mSv limit (range: 0.2 -7.2 mSv). However 6 of 17 children aged 3 years or less had an adjusted do se which exceeded this 1 mSv limit. The dose received by adults during trav el was small in comparison with the total dose received. The median travel dose was 0.03 mSv for 1 h travel (range: 2 mu Sv-0.52 mSv for 1 h of travel time). These data suggest that hyperthyroid patients can continue to be tr eated with radioiodine on an out-patient basis, if given appropriate radiat ion protection advice. However, particular consideration needs to be given to children aged 3 years or younger. Admission to hospital is not warranted on radiation protection grounds.