Outcome and Toxicity of Moderately Hypofractionated Post-Prostatectomy Radiotherapy: A Retrospective Study

<b>Background</b>: In this study, we retrospectively analyzed clinical and toxicity outcomes of 67 prostate cancer (PCa) patients undergoing moderately hypofractionated radiotherapy (RT) after prostatectomy, with adjuvant or salvage intent. <b>Methods</b>: Irradiation was delivered by volumetric modulated arc therapy. The median follow-up was 48 months. The 3- and 5-year biochemical relapse-free survival rates were 80% and 69%. The RT schedule consisted of a median total dose of 67.5 Gy with a median number of 25 fractions and a median fraction dose of 2.7 Gy to the prostate bed (PB) and 60% of patients simultaneously received whole pelvis irradiation (WP; fraction dose: 1.8 Gy, median total dose of 46.8 Gy). <b>Results</b>: The rate of acute toxicity was 54% for gastrointestinal (GI) and 36% for genitourinary (GU). No grade 3 acute toxicity was observed. Late toxicity was as follows: G1, G2, and G3 GI events in 25.5%, 3.6%, and 1.8% of the cases, respectively; G1, G2, and G3 GU events in 37.1%, 11.1%, and 7.4%, respectively. The toxicity-free survival (TFS) curves showed a different trend for acute and late toxicity. TFS was significantly associated with RT volume, except for acute GI toxicity. Specifically, the concomitant irradiation of PB and WP appeared to be a significant risk factor for late GI and GU toxicity (<i>p</i> = 0.029 and <i>p</i> = 0.012, respectively). <b>Conclusions</b>: At the 48-month median timepoint considered by our study, postoperative hypofractionated RT achieved promising results in terms of clinical outcomes with acceptable toxicity. Only the irradiated volume seems to be an important predictor for toxicity.