Robotic Stereotactic Retreatment for Biochemical Control in Previously Irradiated Patients Affected by Recurrent Prostate Cancer.

AIMS: Robotic stereotactic body radiotherapy (rSBRT) to local recurrences emerged as a valuable option for exclusive local failure after prior external beam radiation therapy (EBRT) for localised prostate cancer. The aim of this study was to assess the efficacy and safety of rSBRT in patients experiencing locally recurrent prostate cancer after prior definitive or postoperative radiotherapy using the Cyberknife. MATERIALS AND METHODS: Data from 50 patients were retrospectively reviewed. Local recurrence was assessed by 18F-choline positron emission tomography and pelvic magnetic resonance imaging; a dose of 30 Gy was delivered in five fractions. Prostate-specific antigen (PSA) was assessed at 2 months, 6 months and every 4 months thereafter. Toxicity was assessed according to CTCAE v.4.03. RESULTS: All patients received prior EBRT. The median EQD2 total dose was 74 Gy (60-80 Gy). Eleven patients were receiving androgen deprivation after prior biochemical failure. At 6 months, 41 patients showed a median PSA decline of -77.1% (14.3-99.3%), whereas nine patients experienced a median PSA elevation of +58.7% (0-2300.0%). Biochemical relapse-free survival (BRFS) was 80.0%. Impaired BRFS was correlated with the high-risk category at diagnosis (P = 0.014, hazard ratio 5.61) and ongoing androgen deprivation (P = 0.025, hazard ratio 2.98). Neither clinical variables nor dosimetric parameters were found to be predictive for toxicity. CONCLUSION: Focal rSBRT can achieve durable remission in locally relapsing patients and systemic treatment can be postponed with acceptable toxicity. Accurate patient selection is mandatory to maximise disease control.