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Improving I-131 Outpatient Safety Through Inpatient Data

O Blasi

O Blasi*, N Busse , C Frame , Colorado Assn in Medical Phys (CAMP), Denver, CO


SU-I-GPD-T-4 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Following post-thyroidectomy I-131 administration, the effectiveness of time-dependent restrictions placed on the outpatient depends highly on the ability to accurately predict exposure rate experienced by those coming into contact with the patient. We propose estimation of the biological clearance rate based on available patient diagnostic information.

Methods: Inpatients, administered doses of I-131 ranging from 50 to 212 mCi, were monitored for exposure rates using a calibrated survey meter at a distance of one meter. Measurements of each patient were made sequentially until it was determined that the exposure rate had decreased enough to meet release criteria, typically 2-5mR/hr. In addition, diagnostic information, specifically the presence of metastatic thyroid cancer, was collected and correlated with these exposure rate data.

Results: The exposure rate normalized per mCi of I-131 for all patients was fit with an exponential function with an exponential coefficient of -0.45/hr. Comparing the modeled exposure rate falloff function for patients with and without metastatic cancer resulted in values of -0.39/hr and -0.53/hr, respectively. This difference in biological clearance rates corresponds to a recommended increase of 12 hours of increased isolation for our typical release criteria.

Conclusion: Presence of metastatic cancer at the time of administration of I-131 can lead to a decrease of biological clearance rates of the isotope. This factor should be taken into account when constructing I-131 patient isolation restrictions, and we suggest adding an additional 12 hours to the isolation safety restrictions for patients with metastatic cancer.

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