Does prostate brachytherapy treat the seminal vesicles? A dose-volume histogram analysis of seminal vesicles in patients undergoing combined Pd-103 prostate implantation and external beam irradiation

Purpose: Combined brachytherapy of the prostate and external beam irradiati on (EBRT) of the prostate and seminal vesicles (SV) is becoming a popular t reatment for high-risk prostate cancer. Dose-volume histogram (DVH) analysi s of the SV in patients undergoing this treatment was performed to determin e the dose distribution to the SV and the adequacy of this treatment in pat ients with potential SV involvement. Methods and Materials: Twenty-five con secutive patients were treated with a Pd-103 implant of the prostate alone and 45 Gy of EBRT to the prostate and SV. Attempts were not made to implant the SV but seeds were routinely placed at the junction of the prostate and SV. All patients underwent CT-based postimplant dosimetric analysis 1 mont h after implantation. As part of this analysis, DVH were generated for the prostate and total SV volume (SVT). In addition, the SV was divided into 6- mm-thick volumes identified as SV1, SV2, SV3, SV4, and SV5 starting from th e junction of the prostate and SV and extending distally. DVH were also gen erated for these structures. Delivered dose was defined as the D90 (dose de livered to 90% of the organ on DVH). Results: The median volumes in cc of t he prostate, SVT, SV1, SV2, SV3, SV4, and SV5 were 34.33, 9.75, 2.7, 3.48, 2.92, 3.18, and 1.96 respectively. The SVT contained from 0-9 seeds (median 2). There was little dose delivered to the SVT and SV volumes from the imp lanted prostate. The median D90 values for the prostate, SVT, SV1, SV2, SV3 , SV4, and SV5 were 8615 cGy, 675 cGy, 3100 cGy, 1329 cGy, 553 cGy, 246 cGy , and 67 cGy, respectively. The dose delivered to the prostate covered smal l percentages of SV. The percents of SV volumes covered by the prostate D90 were 11, 35, 3.3, 0, 0, and 0 for SVT, SV1, SV2, SV3, SV4, and SV5, respec tively. Conclusions: DVH analysis of the SV reveals that dose generated fro m an implanted prostate contributes little to the SV. Those patients at hig h risk for SV involvement may be undertreated with combined EBRT to prophyl actic doses and prostate implantation. (C) 1999 Elsevier Science Inc.