Prostatectomy Bed Image-guided Dose-escalated Salvage Radiotherapy (SPIDER): An International Multicenter Retrospective Study.

Background: Management of macroscopic local recurrence (MLR) after radical prostatectomy is a challenging situation with no standardized approach.

Objective: The objective of our study was to assess the efficacy and safety of functional image-guided salvage radiotherapy (SRT) in patients with MLR in the prostate bed.

Design, Setting, And Participants: In this international multicenter retrospective study across 16 European centers, eligible patients were initially treated by radical prostatectomy (RP) with or without pelvic lymph node dissection for localized or locally advanced adenocarcinoma of the prostate.

Outcome Measurements And Statistical Analysis: Prostate-specific antigen (PSA) measured 4 wk after RP was <0.1 ng/ml. All patients presented a biochemical relapse after RP defined by an increase in PSA level of ≥0.2 ng/ml on two successive measures. Only patients with an MLR lesion in the prostatectomy bed visualized on functional imaging (multiparametric magnetic resonance imaging, positron emission tomography/computed tomography [PET/CT] choline, or PET/CT prostate-specific membrane antigen) were eligible. Patients with lymph node, bone, or visceral dissemination at restaging imaging (CT and/or bone scintigraphy and/or magnetic resonance imaging and/or PET) were excluded. Dose escalation was defined as a dose of >66 Gy prescribed to the prostate bed or to MLR. Toxicities were classified using the Common Terminology Criteria for Adverse Events scale, version 4.03. The primary endpoint was progression-free survival (PFS). Secondary outcomes were metastasis-free survival (MPFS), biochemical progression-free survival, and overall survival. Genitourinary (GU) and gastrointestinal (GI) toxicities were analyzed.

Results And Limitations: Between January 2000 and December 2019, 310 patients received at least one dose escalation on MLR and 25 patients did not receive any dose escalation. The median PSA level before SRT was 0.63 ng/ml (interquartile range [IQR], 0.27-1.7). The median follow-up was 54 mo (IQR, 50-56). Five-year PFS and MPFS were 70% (95% confidence interval [CI]: [64; 75]) and 84% (95% CI: [78; 88]), respectively. Grade ≥2 GU and GI late toxicities were observed in 43 (12%) and 11 (3%) patients, respectively. When the prescribed dose on the MLR lesion was ≥72 Gy, an improvement in 5-yr PFS was found for patients received at least one dose escalation (73% [95% CI: 65-79]) vs 60% [95% CI: 48; 70]; p = 0.03).

Conclusions: In this contemporary study integrating functional imaging data, we found potential efficacy of SRT with dose escalation ≥72 Gy for patients with MLR in the prostate bed and with an acceptable toxicity profile. Prospective data exploring this MLR dose escalation strategy are awaited.

Patient Summary: In this report, we looked at the outcomes from salvage radiotherapy for prostate cancer and macroscopic relapse in a large European population. We found that outcomes varied with prostate-specific antigen at relapse, Gleason score, and dose escalation. We found potential efficacy of salvage radiotherapy with dose escalation for macroscopic relapse in the prostate bed, with an acceptable toxicity profile.