Evaluation of radiation doses to relatives of patients treated by I-131 for thyroid carcinoma

Objectives Patients treated with I-131 for thyroid carcinoma are source of potential radiation exposure for other individuals. To provide more reliable information to patients and relatives, this pilot study evaluated the radiation dose received by family members after discharge from the hospital.

Methods Thirty-five consecutive thyroid cancer patients who were treated post-operatively with 3.7 GBq of I-131 following thyroid treatment withdrawal were included in the study after informed consent. A calibrated NaI(Tl) counting device was implemented in the treatment room to measure whole-body retention during hospitalization (3 days). Additional dose rate measurements were performed using an ionization chamber before discharge from the hospital. An electronic dosimeter (sensitivity close to 1 μSv) was given to 46 family members who wore it on their chest when they were at home, during 7 days. This allows to describe both total dose and dose delivery. Measurements were corrected for natural background. A questionnaire was completed to depict the family’s habit and condition of life.

Results At discharge, the median residual activity was 148 (47 - 529) MBq. The median effective half-life was 0.58 (0.38 - 1.09) days and the dose rate at 1 meter from thyroid bed ranged from 0.8 to 14 µSv/h. The median dose received by relatives during 7 days was 27 (3 - 193) µSv, and the time of contact (nearby the patient) was 38 (3 - 136) hours. In most cases, the dose was received during the first 3 days following discharge.

Conclusions The results highlighted the low level of radiation received by the relatives of patients, that are far below the ICRP recommendation for public.