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.