Examining the role of elective pelvic radiotherapy in patients Diagnosed with high- and very High-Risk Non-Metastatic prostate cancer.

Introduction: In the treatment of node-negative, non-metastatic high-risk (HR) and very high-risk (VHR) prostate cancer, the necessity of elective pelvic irradiation is controversial. According to our in-house treatment protocol - elective pelvic irradiation is generally omitted for HR and VHR patients over the age of 70 or those in poor general health due to its toxicity. Objective: To retrospectively examine the outcome for HR and VHR prostate cancer patients treated with elective whole pelvic radiotherapy (WPRT) versus prostate-only radiotherapy (PORT). Materials and Methods: The study included 434 patients treated with definitive radiotherapy, 203 patients received PORT (HR: 127, VHR: 76) and 231 WPRT (HR: 113, VHR: 118) with a boost to the prostate. Patients also received 2-3 years of androgen deprivation. Patients' average age who received PORT vs. WPRT was 73.9 ± 4.3 years vs. 66.4 ± 5.4 years respectively. An inverse propensity score weighting method was utilized to create homogeneous WPRT and PORT treatment groups that are balanced for T stage, PSA, and Gleason score, but not for age. The survival outcomes for HR and VHR subgroups were examined depending on whether they received WPRT or PORT. Biochemical- (BRFS), local- (LRFS) and regional relapse-free survival (RRFS), distant metastasis-free- (DMFS), disease-free- (DFS), failure-free- (FFS), and overall survival (OS) were compared using the Kaplan -Meier method and Cox regression analysis. Results: The median follow-up time was 76 months (3-134 months). In the VHR subgroup five-year outcomes showed a significant advantage for patients receiving WPRT vs. PORT in BRFS (82.2 % vs. 73 %; p = 0.028), in DMFS (87.5 % vs. 73.6 %; p = 0.025), in DFS (86.1 % vs. 70.5 %; p = 0.012), and in FFS (82.3 % vs. 68.9 %; p = 0.005), respectively. The OS (92.8 % vs. 81.8 %; p = 0.056) showed a trend favoring the WPRT group. There was no significant difference between WPRT vs. PORT in LRFS (95.8 % vs. 96.4 %; p = 0.763) and RRFS (95.8 % vs. 89.9 %; p = 0.099). On the contrary, in the HR group, no significant survival differences were observed between WPRT vs. PORT groups: BRFS 93.0 % vs. 93.3 % (p = 0.978), LRFS 99.0 % vs. 100 % (p = 0.120), RRFS 98.2 % vs. 95.1 % (p = 0.813), DMFS 93.5 % vs. 95.5 % (p = 0.793), DFS 91.7 % vs. 92.9 % (p = 0.691), FFS 89.5 % vs. 90.9 % (p = 0.853), OS 91.0 % vs. 87.7 % (p = 0.407). Conclusion: Based on our retrospective data elective pelvic irradiation can be omitted in HR patients, especially over the age of 70. For VHR patients, elective pelvic irradiation should be considered even for the subgroup of elderly patients.