Peking University First Hospital Beijing, State...
Y. Gao, X. Gao, X. Qi, and J. Y. Chen; Department of Radiation Oncology, Peking University First Hospital, Beijing, China
Purpose/Objective(s): To evaluate the association between genitourinary (GU) toxicity and planning dose-volume parameters, and to investigate the effectiveness of the innovative urinary protection technique (UPT) in reducing radiation dose to the urethra and trigone. Materials/
Methods: A total of 62 patients with prostate cancer treated with radical radiotherapy from August 2022 to December 2023 were collected, and the prescribed dose was 70Gy/2.8Gy/25f. They were stratified into two groups according to toxicity, including one low-grade group (grade = 1, n = 36) and one high-grade group (grade = 2, n = 26). The urethra was delineated in the 3D T2WI sequence of MR. The dose–effect relations of the urethra and bladder dose-volume parameters, separately, and GU toxicity grade=2 (CTCAE 5.0) were analyzed. An additional urinary protection plan was created for the high-grade group as a self-control plan. UPT means the whole bladder and urethra were divided into the inside part and the outside part of the PTV to limit the maximum and mean doses, respectively. Plan differences were analyzed with the Wilcoxon signed-rank test. Continuous variables were described as means (standard deviation) and compared with the Student’s t-test. Statistical software was employed for statistical analysis, and p < 0.05 was considered statistically significant. Results: There was no significant difference between the two groups in V40~60% of the whole bladder. The V75cc in the trigone and V73.5cc in the urethra of the high-grade group were 0.35 ± 0.49 and 0.92 ± 0.74 respectively, which were significantly higher than those in the low-grade group (0.02 ± 0.05 and 0.49 ± 0.48) (P < 0.05). Grade = 2 GU toxicity was significantly associated with high-dose volumes of trigone >75Gy and urethra >73.5Gy. D95% of PTV using UPT was comparable to conventional planning (70.52 ± 0.14 and 70.64 ± 0.48) (P < 0.01). The D0.03cc of the trigone (72.66 ± 0.80Gy) and the maximal and mean doses of the prostatic urethra (73.73 ± 0.84Gy and 44.77 ± 10.61Gy, respectively) and external prostatic urethra (55.49 ± 16.37Gy and 11.75 ± 5.05Gy, respectively) in the UPT plan were significantly lower than those (trigone 75.71 ± 0.76Gy, prostatic urethra 76.23 ± 0.96Gy and 47.88 ± 11.26Gy, external prostatic urethra 62.76 ± 11.78Gy and 17.63 ± 6.97Gy, respectively) in the non-UPT plan. Conclusion: For prostate moderate-fractionated radiotherapy, grade = 2 GU toxicity was significantly associated with hot spots in the trigone and urethra. The urinary protection technique has significant dosimetry advantages by reducing urinary high-dose volume without compromising the target coverage.