Radiation safety post liver Y90 therapy - Is the hospital ward safe?

Objectives: Liver radiomicrospheres treatments are carried out with Yttrium 90 (Y90) -resin incorporated in biocompatible microspheres. Y90 is a pure beta-particle-emitter with a physical half-life of 64.2 hours, 0.94 MeV decay energy, and an average penetrative depth of 2.4mm in human tissue. The patients in our institution are administered with a mean activity of 0.92 Gbq (+ 0.42). When patients are warded post-treatment to monitor their clinical conditions, these patients become a radiation source/concern mainly to the nurses and housekeepers during the hospital stays, and to visiting family members. The study strives to explore if the concerns are warranted.

Methods: The external radiation exposure rates of 30 patients were measured using a calibrated ionization survey meter. The measurements were taken at 1 meter, 2 meters, and 3 meters from the patients’ supine body axis (liver to pelvis), immediately post therapy, and at 24 hours and 48 hours. Urinary excretions in 8 patients were also measured to estimate the potential risk from the discharge into the sewage system. Radiation levels of general/biohazard wastes, toilet bowl, and external radiation exposure rates were also measured.

Results: Dose rates of 16.6 (+ 1.3), 8.5 (+ 1.2), and 1.1 (+ 1.1) µSv/hr were measured at 1, 2, and 3 meters respectively immediately post therapy. All patients had exposure rates below 1 µSv/hr by 24 hours at 1 meter from the liver. The urinary bag had a maximum dose rate recorded at 1.2 µSv/hr at 6 hours post therapy. One unflushed toilet had a maximum reading at 0.9 µSv/hr, 6.2 hours post-therapy. Insignificant radiation dose readings were recorded from the waste bins and the room environment. The calculated assumption of a housekeeper at 1 meter from a patient at these dose rates for an average continuous 0.25 hours showed insignificant radiation exposure. The conservative assumption of a nursing staff or family member at an interaction distance of 1 meter from a patient at these dose rates for a continuous 6 hours based on the measurements is less than 0.1 mSv of radiation dose exposure, with decay taken into consideration. Mean TEDE dose was 0.04 mSv.

Conclusions: The beta dose delivery is mainly confined to the liver with minimal biologic elimination of Y90. There is minimal biologic elimination of Y90 from the patient’s bodies, with only trace amounts detected. Routine housekeeping of the room during and post patients’ stay/discharge is safe with unwarranted radiation concerns.