Predictive estimate of effective dose to family members from patients of thyroid carcinoma treated with radioiodine

The radiation dose received by any member of the family attending to the patient released after 131I therapy, primarily will be influenced by the whole body activity retained by the patient, the effective half-life of 131I in the body and the length and proximity of contact with the patient i e. the occupancy factor. According to International Commission of Radiological Protection (ICRP 60), the annual effective dose limit for the members of the public is 1 mSv. In the reports available of the doses received by the family members from patients treated with 131I, the doses either have been estimated using dosimeters worn by the relatives for a specific time period or have been theoretically calculated considering physical decay of the radionuclide. In the present study, the likely doses to the family members were estimated based on calculations, wherein the actual effective half-life of 131I and whole body activity of 131I have been used. Two distances (0.6 m and 1 m) and 4 different occupancy factors (0.125, 0.25, 0.75 and 1), were considered for these calculations. In India, the patient is released from the hospital when the whole body 131I activity is less than or equal to 555 MBq (15 mCi), a limit stipulated by AERB. The objective of retaining the patient in the hospital till the whole body retained activity has fallen below the recommended limit is to minimize the radiation exposure to the general public and family members. Our predictive estimated values of effective dose suggests that with proper instructions of radiation safety and hygiene to the patient, doses to the family members and public can be kept below the limit of 1 mSv. Since some individuals in the family will be knowingly and willingly involved in the care, support and comfort of the patient, a dose of more than 1 mSv is acceptable, however, it should be constrained so that it does not exceed 5 mSv. (author)