Results of Dose-adapted Salvage Radiotherapy After Radical Prostatectomy Based on an Endorectal MRI Target Definition Model

OBJECTIVES: To assess the outcome of patients treated with a dose-adapted salvage radiotherapy (SRT) protocol based on an endorectal magnetic resonance imaging (erMRI) failure definition model after radical prostatectomy (RP). METHODS: We report on 171 relapsing patients after RP who had undergone an erMRI before SRT. 64 Gy were prescribed to the prostatic bed with, in addition, a boost of 10 Gy to the suspected local relapse as detected on erMRI in 131 patients (76.6%). RESULTS: The 3-year biochemical relapse-free survival (bRFS), local relapse-free survival, distant metastasis-free survival, cancer-specific survival, and overall survival were 64.2±4.3%, 100%, 85.2±3.2%, 100%, and 99.1±0.9%, respectively. A PSA value >1 ng/mL before salvage (P=0.006) and an absence of biochemical progression during RT (P=0.001) were both independently correlated with bRFS on multivariate analysis. No significant difference in 3-year bRFS was observed between the boost and no-boost groups (68.4±4.6% vs. 49.7±10%, P=0.251). CONCLUSIONS: A PSA value >1 ng/mL before salvage and a biochemical progression during RT were both independently correlated with worse bRFS after SRT. By using erMRI to select patients who are most likely expected to benefit from dose-escalated SRT protocols, this dose-adapted SRT approach was associated with good biochemical control and outcome, serving as a hypothesis-generating basis for further prospective trials aimed at improving the therapeutic ratio in the salvage setting.