Contamination During a Brachytherapy Procedure

Abstract

This paper describes an unusual contamination incident that occurred during the treatment of a prostate cancer patient with seeds containing ¹²⁵I. The incident became particularly interesting as the radiation safety procedures in place prior to the incident were, in fact, inappropriate for the type of incident that occurred, resulting in a series of response errors. Strands containing 108 ¹²⁵I seeds with a total activity of 1.61 GBq (43.6 mCi) were implanted into a patient’s prostate and the patient was sent to the recovery room. A radiation survey detected radiation levels of up to 15 μR h⁻¹, 10 cm from the surface of the implantation needles. Multiple individuals entered the room and were potentially exposed to contamination. Contamination was detected in a sample of the patient’s urine, indicating that one or more implanted seeds were leaking. Initial test results for staff showed that 12 of 15 had thyroid levels potentially above their corresponding minimum detectable activity levels, with calculated thyroid burdens ranging from 0.17 kBq to 0.94 kBq, but, subsequent measurements, using each staff member’s thigh counts as background, suggested that no staff member had been contaminated. The patient showed high uptake of ¹²⁵I in his neck 10 d following the incident, estimated to correspond to an initial thyroid burden of 58 kBq. The possibility of contamination was not immediately considered due to the suspicion of the more common problem of a misplaced source. The initial measurements suggesting thyroidal contamination in staff point to an error in our thyroid screening method.