8096 Optimization of Radiation Safety Release Instructions After Iodine-131 Treatment for Differentiated Thyroid Cancers

Abstract Disclosure: A.H. Smith: None. T. Greist: None. Introduction: Iodine-131 (I-131) is a common therapy for treatment of differentiated thyroid cancers (DTC); however its radioactivity poses a risk to public health. There is wide inter-facility variation in release instructions to minimize incident exposure to other individuals. Isolation measures to reduce gamma exposure may pose harm to an individual's mental or physical health, especially in new parents or patients who require caregivers. Most studies estimating incident exposure utilize cumulative dosimetry to estimate duration of safety release instructions, but this relies on expert assumptions of the clearance of I-131, which is altered in patients who have had their thyroid removed. Measuring real-time longitudinal gamma exposure would optimize recommendations to balance the radiation safety risks with the risks associated with isolation. Objective: Quantify real-time longitudinal incident gamma radiation exposure to others from patients with DTC status post thyroidectomy treated with I-131. Methods: Patients were asked to measure exposure rates at a distance of one meter three times a day for fourteen days, using a portable ion chamber at their homes. Exposure rates over time were used to form an exponential decay model and to estimate the time after which cumulative exposure is below a reasonably low threshold. Results: 32 patients were included in the study. The average effective half-life was 15.8 hours. Exposure readings over time were best fit with an exponential decay model using one decay rate, rather than a model that uses separate extrathyroidal and thyroidal decay rates. Among patients administered less than 114 mCi, cumulative gamma exposure is less than 100 mR after 24 hours of isolation. Between 114 and 163 mCi, cumulative gamma exposure is less than 100 mR after 48 hours of isolation. Conclusion: Cumulative gamma radiation exposure at one meter was found to be low enough to consider re-evaluating isolation protocols and safety release instructions for long-term distancing in patients status post thyroidectomy treated with I-131. Presentation: 6/1/2024