Radiation safety of receptive anal intercourse with prostate cancer patients treated with low-dose-rate brachytherapy

PURPOSE: Prostate low-dose-rate (LDR) brachytherapy involves implantation of radioactive seeds permanently into the prostate gland. During receptive anal intercourse, the penis of the partner may come in close proximity to the implanted prostate gland. We estimate the potential intrarectal dose rates and suggest guidance on radiation precautions. METHODS AND MATERIALS: One hundred two patients were included in the study. After implantation, with patients under anesthesia in the dorsal lithotomy position, a new set of ultrasound (US) images and a CT scan were obtained. The images were fused, radioactive seeds and US probe locations were determined on the CT, and prostate, bladder, and rectal contours were drawn on the US. Dose rates (cGy/h) were calculated for the portion of the US probe spanning the prostate for several dose-volume histogram parameters. RESULTS: Twenty patients were treated with I-125 and 82 patients with Pd-103. Average dose rates at Day 0 to the portion of the US probe spanning the prostate were 2.1 1.3 cGy/h and 2.5 +/- 0.8 cGy/h for patients treated with I-125 and Pd-103, respectively. After 60 days, average calculated probe dose drops to 1.0 +/- 0.6 cGy/h and 0.2 +/- 0.1 cGy/h for I-125 and Pd-103, respectively. CONCLUSIONS: During the immediate weeks after prostate seed implant, the estimated intrarectal dose rates are higher in Pd-103 compared to I-125. As Pd-103 decays faster than I-125, 2 months after the implant, radiation exposure from Pd-103 becomes lower than I-125. Receptive anal intercourse time should be kept as low as possible during 2 and 6 months after low-dose-rate brachytherapy of the prostate with Pd-103 and I-125, respectively. (C) 2016 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.