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Hypofractionation in salvage radiotherapy (SRT) for biochemical recurrence (BCR) of prostatic cancer after prostatectomy  is a debated issue. We report the outcomes of 2 moderately hypofractionated schedules in pts who received SRT to prostate bed for BCR.

Pts treated with Image Guided-VMAT and a total dose of 65 Gy/26 fractions (Group A; BED=173.4 Gy for α/β=1.5) or 66 Gy/30 (Group B; BED=162.8 Gy for α/β=1.5) were considered. Inclusion criteria were: pN0/pNx, PSA at BCR ≥ 0.2 ng/ml and ≤ 1 ng/ml, no evidence of pelvic/extrapelvic disease at restaging (when indicated), no pelvic irradiation or boost on macroscopic local recurrence, follow-up ≥2 years and available pre/post SRT data. Concomitant ADT was used prevalently in pts with high risk features. Early and late toxicities were assessed using CTCAE Vers. 4.0. 

150 pts were identified (Tab 1). Median follow-up was 67  months (IQR: 52-81) in group A and 38 (IQR: 30-46) in Group B (p<0.001). 3-year recurrence rate of biochemical, local and distant failure in Group A and Group B were  30.6% and 32.2% (p=0.928), 4.2% and 6.1% (p=0.562), 23.5% and 25.9% (p=0.961), respectively (Fig 1). Among pts with a distant failure pattern of relapse, 23 pts (82.1%) in Group A and 15 (71.4%) in Group B had oligometastatic relapse (p=0.494); 5 pts (17.9%) in Group A and 6 (28.6%) in Group B had polimetastatic relapse. 5 pts in Group A (2 oligoprogressive pts) and 4 pts in Group B (1 oligoprogressive pt) developed mCRPC; median hormone-sensitive time was 57 months in Group A and 14 in Group B. 3-year OS was 100% in group A and 92.2% pts in Group B (p=0.158), disease specific OS was 100% in Group A and 96.1% in Group B (p=0.319). On multivariate analysis, ISUP score ≥4 was associated with worse biochemical failure (HR=2.29, 95% CI: 1.25-4.23; p=0.008); ISUP score≥4 (HR=2.08, 95% CI: 1.05-4.10, p=0.036) and time to BCR<24 months (HR=2.24, 95% CI: 1.09-4.62, p=0.028) were significantly associated with worse distant failure. Among pts undergoing concomitant ADT, pts in Group A reported a lower rate of biochemical (HR=0.19; 95% CI: 0.07-0.52) and distant failure (HR=0.17; 95% CI: 0.06-0.49) than Group B (Fig 1). A significantly higher late genitourinary toxicity rate was observed in Group A (p=0.032).

Although the study was limited by the retrospective design, the relative shortness of the median follow-up and the small number of pts in some of the evaluated subgroups, our analysis did not show any significant difference in outcome between the 2 treatment schedules except for a greater late genitourinary toxicity in the higher BED group. Our finding of improved biochemical and distant disease control with a higher BED hypofractionation and concomitant ADT indicates the need to improve the selection of pts who may benefit from integrated and intensificated SRT.