Thyroid remnant ablation with 1110MBq of 131I in outpatients: measurement of effective dose to household members and establishment of safety precautions

Aim. The aim of this study was to establish and confirm the safety of administering 1110MBq of I-131 to outpatients. Methods: Total radiation exposure from patients to household members was hypothesized from the measured dose rate at 1 m when the patient is released. Actually we also measured the effective dose to household members who assisted outpatients during the first 7 days after the administration of I-131 by personal dosimeter. A list of radiation safety precautions is given to the patient and household members. Behavioral reports about the distances and times of close contact throughout the 7 days are requested of each household member. Results: The effective dose measured using the personal dosimeter to all household members employing several safety precautions was confirmed to be lower than the hypothesized dose calculated using our formula. And the mean whole-body effective dose rate over the 7 days in household members was 0.05 +/- 0.08 (range, 0.05 to 0.43) mSv, which specify that radiation exposure to household members of the outpatients who have just received ablative radiation therapy must be below 5.0 mSv/event. Conclusion: Remnant thyroid ablation with 1110MBq for outpatients showed that the radiation doses to household members were within the recommended constraint dose according to several safety precautions. The method of returning home after remnant thyroid ablation is thought to be the most important factor that determines the effective dose to household members of outpatients.