Stereotactic reirradiation with CyberknifeR for locally recurrent prostate cancer, long-term toxicity and clinical outcomes from a monocentric cohort.

Abstract

Up to 47% of patients with localized prostate cancer (PCa) treated with radiotherapy (EBRT) eventually develop local recurrence. To date, no clear consensus exists on optimal management. A growing body of interest supports the use of stereotaxic re-irradiation (rSBRT), with promising oncological outcomes and low toxicity profile. We collected a single-center case series of locally recurrent PCa who underwent re-irradiation after a previous course of postoperative or definitive radiotherapy. Data from 101 patients treated at our institution for locally recurrent PCa from June 2012 to June 2021 were retrospectively collected. Patients underwent rSBRT with CyberKnife system (Accuray Inc., Sunnyvale, CA, USA), delivered to intraprostatic or macroscopic recurrences within the prostate bed, for a total dose of 30Gy in 5 fractions. All patients received prior EBRT. The median EQD2 total dose was 75.0Gy (range, 60-80Gy). Thirty-two (32%) patients were receiving androgen deprivation therapy (ADT) after prior biochemical recurrence. After a median follow-up of 57.8months, BR occurred in 55 patients (54.5%), with a median BR-free survival (BRFS) of 40.4months (95% C.I. 34.3-58.3). Thirty-two patients (31.7%) developed metastatic disease, with a median metastasis-free survival (MFS) not reached. PSA ≥ 2.5ng/ml and ADT were associated with worst BRFS (26.06 vs. 39.3months, p = 0.03 and 22.7 vs. 27months, p = 0.01, respectively). Castration-resistant status and ADT were found to be predictive of worst MFS (34.1 vs. 50.5months, p = 0.02 and 33.5 vs. 53.1months, p = 0.002, respectively). Concomitant ADT was confirmed as an independent factor for MFS (HR 4.8, 95% CI 1.5-10.6, p = 0.007). No grade > /2 adverse were recorded. After almost 5years of follow-up, with a median BRFS of 40.4months and no grade ≥ 2 AEs, CyberknifeR rSBRT proved effective and safe in a cohort of 101 patients affected by locally recurrent PCa.