Correlation Between Dosimetric Parameters and Late Rectal and Urinary Toxicities in Patients Treated With High-Dose-Rate Brachytherapy Used as Monotherapy for Prostate Cancer

Purpose: To evaluate the correlation between dosimetric parameters and late rectal and urinary toxicities in high-dose-rate brachytherapy (HDR-BT) used as monotherapy for prostate cancer. Methods and Materials: The data of 83 patients treated with HDR-BT alone for prostate cancer from 2001 through 2005 at Osaka University Hospital were analyzed. Median follow-up time was 36 months (range, 18-70). The total prescribed dose was 54 Gy in nine fractions over 5 days. Correlation between dosimetric parameters and late toxicities was examined. Results: The means of V30, V40, V50, V60, V70, D1cc, D2cc, D5cc, and D10cc of the rectum were significantly higher in 18 patients who presented with late rectal toxicity (Grades 1-3 rectal bleeding) than in the other 65 patients who did not. A significant difference was observed for D1cc-10cc but not for D5-90. The statistically most significant difference was observed for V40 and D5cc. Late rectal toxicity rate was significantly higher for patients with rectal V40 ≥ 8 cc than those with the rectal V40 < 8 cc (42% vs. 8%; p < 0.001), as well as for patients with rectal D5cc ≥ 27 Gy compared with those with rectal D5cc < 27 Gy (50% vs. 11%; p < 0.001). Dosimetric parameters of the urethra of 15 patients with late urinary toxicity were not significantly different from the 68 patients without toxicity. Conclusion: Rectal V40 < 8 cc and D5cc < 27 Gy may be dose-volume constraints in HDR-BT used as monotherapy for prostate cancer.