A practical guideline for the release of patients treated by I-131 based on Monte Carlo dose calculations for family members.

We recently published effective doses per time-integrated activity (mSv MBq(-1) s(-1)) for paediatric and adult family members exposed to an adult patient released from hospital following I-131 therapy. In the present study, we intend to provide medical physicists with a methodology to estimate family member effective dose in daily clinical practice because the duration of post-radiation precautions for the patient-family member exposure scenario has not been explicitly delineated based on the effective dose. Four different exposure scenarios are considered in this study including (1) a patient and a family member standing face to face, (2) a patient and a family member lying side by side, (3) an adult female patient holding a newborn child to her chest and (4) a one-year-old child standing on the lap of an adult female patient following her I-131 therapy. The results of this study suggest that an adult female hyperthyroidism (HT) patient who was administered with 740 MBq should keep a distance of 100 cm from a 15-year-old child for six days and the same distance from other adults for seven days. The HT female patient should avoid holding a newborn against her chest for at least 16 days following hospital discharge, and a female patient treated with 5550 MBq for differentiated thyroid cancer should not hold her newborn child for at least 15 days following hospital discharge. This study also gives dose coefficients allowing one to predict age-specific effective doses to family members given the measured dose rate (mSv h(-1)) of the patient. In conclusion, effective dose-based patient release criteria with a modified NRC two-component model provide a site medical physicist with less restrictive and age-specific radiation precaution guidance as they fully consider a patient's iodine biokinetics and photon attenuation within both the patient and the exposed family members.