Stereotactic reirradiation for local prostate cancer recurrence: Mono-institutional experience of 108 patients.

365 Background: The aim of this study was to report the efficacy and toxicity of salvage stereotactic body radiation therapy (SBRT) for local prostate cancer recurrence after radiotherapy. Methods: We retrospectively reviewed a total of 108 medical records of patients treated with salvage SBRT for prostate cancer recurrence, between July 2015 and February 2021 in our institution. Patients who had initial radical prostatectomy were excluded. The median time interval between the two radiation treatments was 9 years (range, 3-20 years). All the patients had biochemical recurrence, with a PSA of 3.5 ng/mL (range, 1.8-43 ng/mL). Local recurrence was to be proven by biopsies, without distant lymph node or metastasis. The local recurrence was visible in 82% and 99% of patients on mpMRI and choline/PSMA PET/CT, respectively. The salvage treatment consisted in SBRT at a total dose of 36 Gy in six fractions delivered every other day, associated with androgen deprivation therapy in 44% of patients. We reported efficacy and toxicity (according to CTCAE v 4.03 classification) after salvage SBRT. Results: Median follow-up was 19.6 months (range, 2.3-67 months). Two year biochemical recurrence-free survival and lymph node/metastases free survival rates were 76% (95% CI: 66-87%) and 88% (95% CI: 80-96%), respectively. Regarding acute toxicity, rates of grade 2 and 3 GU toxicities were 27% and 2%, respectively. Rate of grade 2 GI toxicity was 2%, without grade ≥3. Regarding late toxicity, 2 year rates of grade 2 and 3 GU toxicities were 50% (95% CI: 44-56%) and 8% (95% CI: 2-14%), respectively. One patient experimented a grade 4 GU toxicity (bladder necrosis requiring a cystectomy) 8 months after SBRT. Two year rate of grade 2 GI toxicity was 2 (95% CI: 0-5%), without grade ≥3. Conclusions: The main toxicity of prostate salvage SBRT is GU. With a short follow-up, a subset of patients may be controlled by the salvage treatment.