Toxicity Comparison between a Four-Week Moderate Hypofractionation and a Six-Week Conventional Fractionation in the Post-Prostatectomy Salvage Radiotherapy for Prostate Cancer.

[INTRODUCTION] We compared toxicity profiles of moderate hypofractionated radiotherapy (HFRT) and conventional radiotherapy (CFRT) in salvage radiotherapy (SRT) for prostate cancer patients who underwent radical prostatectomy.

[PATIENTS AND METHODS] We retrospectively reviewed prostate cancer patients who underwent SRT between 2022 and 2023. Two groups were analyzed: CFRT (66 Gy in 30 fractions) and HFRT (55 Gy in 20 fractions). Propensity score matching was performed using variables associated with toxicity outcomes including androgen deprivation therapy usage, anticoagulant usage, diabetes mellitus, baseline genitourinary symptoms, SRT field, and boost irradiation. Follow-up evaluations were conducted every 3 months for the first year and every 6 months thereafter, for up to 2 years. The primary endpoint was acute and late genitourinary (GU) and gastrointestinal (GI) toxicity.

[RESULTS] A total of 70 CFRT and 66 HFRT patients were included. After matching, 112 patients (56 per group) were analyzed with median follow-up of 27.8 and 24.8 months, respectively. There was no significant difference in baseline toxicities before SRT between the 2 groups. GU toxicities at 3 months were comparable except for grade 1 urgency, which was more frequent in CFRT (30.4% vs. 14.3%, P = .041) but resolved by 1 year. Late GU toxicities at 1 or 2 years were not significantly different between the 2 groups. No grade ≥ 3 late GU toxicities were observed. For GI toxicities, grade 3 rectal bleeding occurred in 3.6% of CFRT and 1.8% of HFRT patients within 1 year (P = 1.000). Aside from more grade 2 diarrhea at 3 months in CFRT (26.8% vs. 8.9%, P = .014), no significant differences in GI toxicity were found.

[CONCLUSION] Four-week HFRT for SRT showed favorable long-term toxicity outcomes, sustained for up to 2 years and comparable to those of 6-week CFRT.