Objective: Thyroid cancer patients treated with I-131 are potential source of radiation exposure to relatives who are
knowingly and willingly exposed to ionizing radiation as a result of providing comfort to patients undergoing I-131 therapy.
This study aims to determine radiation dose received by relatives who care for non self-supporting I-131 patients at Siriraj Hospital.
Material and Method: Twenty caregivers of 20 patients underwent I-131 therapy for thyroid cancer with a standard protocol were given specific instructions with regard to radiation safety and provided with electronic digital dosimeter to continuously measure radiation dose received on daily basis, three days in the hospital. On the day patient is released, thyroid uptake estimates were performed to assess internal radiation dose received by caregivers.
Results: The 3-day accumulative doses to caregivers to patients receiving 150 mCi (n = 11) and 200 mCi (n = 9) of I-131 ranged from 37 to 333 μSv and 176 to 1,920 μSv respectively depending on the level of supports required. Thyroid uptake estimates in all caregivers were undetectable. Dosimeter indicated a maximum whole-body dose of 1.92 mSv was more than the public dose limit of 1 mSv but within the dose constraint of 5 mSv for caregivers.
Discussion: Radiation dose to caregivers of a non self-supporting hospitalized patient undergoing I-131 therapy were well below the limits recommended by the ICRP. The patients can be comforted with confidence that dose to caregivers will be less than the limit.
Conclusion: This study provides guidance for medical practitioners to obtain practical radiation safety concerns associated with hospitalized patients receiving I-131 therapy especially when patient needs assistance.

Keywords: Radioiodine therapy, Caregivers, Dose constraints