Salvage prostate re-irradiation using high-dose-rate brachytherapy or focal stereotactic body radiotherapy for local recurrence after definitive radiation therapy

Background: Optimal management of locally recurrent prostate cancer after definitive radiation therapy is still challenging. With the development of highly accurate radiotherapy devices, prostate salvage re-irradiation might generate lower toxicity rates than classical salvage therapies. We retrospectively evaluated the toxicity and the feasibility of a prostate re-irradiation after definitive radiation therapy failure. Two modalities were investigated: high-dose-rate brachytherapy (HDRB) on whole prostate gland and focal stereotactic radiotherapy (SBRT) using CyberKnife (R) linac. Methods: Between 2011 and 2015, 28 patients with imaged and/or biopsy-proven intra-prostatic recurrence of cancer after definitive radiation therapy underwent a salvage re-irradiation using HDRB (n = 10) or focal SBRT (n = 18). The schedule of re-irradiation was 35 Gy in 5 fractions. Biological response (defined as post-salvage radiation PSA variation) and biochemical no-evidence of disease (bNED) were evaluated in the whole cohort. For patients who had a positive biological response after salvage radiation, biochemical recurrence (BCR) and survival after salvage radiotherapy were evaluated. Post-salvage toxicities were assessed according to the Common Terminology Criteria for Adverse Events (CTCAE) v4.03 and were compared to baseline status. Results: Within a median follow-up of 22.5 months (IQR = 8-42), 9 (90%) patients experienced a positive biological response after salvage HDRB and 5 (50%) remained bNED at the end of the follow-up. Among patients who initially responded to salvage HDRB, the BCR rate was 44.4% after a median interval of 19.5 months (IQR = 11.5-26). Only one patient experienced a transient grade 3 urinary complication. In the SBRT group, the median follow-up was 14.5 months (IQR = 7-23) and 10 (55.6%) out of the 18 patients remained bNED. Among the 15 patients who initially responded to salvage SBRT, 5 (33.3%) experienced a BCR. One patient experienced a transient grade 4 urinary complication. At the end of the follow-up, all evaluated patients had a urinary status grade variation = <= + 1 grade. No grade 3-4 digestive toxicity was observed. Conclusions: Salvage prostate re-irradiation for locally recurrent cancer is feasible and generate low toxicities rates when using with HDRB or focal SBRT. However, further investigations are necessary to confirm these findings and to determine predictive features for patients who might benefit from such an approach.