Dosimetry of anal radiation in high-dose-rate brachytherapy for prostate cancer

PURPOSE: The objective of this study is to determine the radiation dose to the anus during brachytherapy using high-dose-rate Ir-192 sources. METHODS AND MATERIALS: Thermoluminescence dosimeters were used for measuring the dose to the distal part of the anus in 10 patients, and in a prostate phantom to measure the radiation dose during the transport of the radiation source. RESULTS: The measured dose to the anus in vivo was on average 0.85 Gy (range, 0.48-1.37 Gy) per treatment. The transport dose using 15 and 19 needles in the prostate phantom was 0.07 and 0.08 Gy, respectively. CONCLUSIONS: The dose delivered to the anus using high-dose-rate brachytherapy with Ir-192 sources is quite low. There is a contribution to the anal radiation dose during the transport of the Ir-192 source into the needles. However, in clinical practice when using 15-20 needles, the dose from transporting the Ir-192 source can be ignored.