Prognostic significance of the mEPE score in intermediate-risk prostate cancer patients undergoing ultrahypofractionated robotic SBRT.

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This study aimed to evaluate the prognostic significance of magnetic resonance imaging (MRI) parameters on biochemical failure-free survival (BFS) in patients diagnosed with intermediate-risk prostate cancer and treated with robotic ultrahypofractionated stereotactic body radiotherapy (SBRT) without androgen deprivation therapy (ADT). Aretrospective analysis was conducted in patients with intermediate-risk prostate cancer undergoing robotic SBRT delivered in five fractions with atotal radiation dose of 35-36.25 Gy. The primary endpoint was biochemical failure as defined by the Phoenix criteria. Among other clinicopathological data, Tstage, Prostate Imaging-Reporting and Data System (PI-RADS) score, and multiparametric magnetic resonance imaging-based extra-prostatic extension (mEPE) score were collected and analyzed using the log-rank test. Atotal of 74patients were eligible for analysis. Median age at treatment was 68.8 years and median prostate volume was 47.8cm3. Fifty-four and 14patients were diagnosed with Gleason scores 7a and 7b, respectively. In total, 40patients were classified as having unfavorable intermediate-risk prostate cancer according to American Urological Association/American Society for Radiation Oncology/ Society of Urologic Oncology (AUA/ASTRO/SUO) guidelines. The median follow-up was 30months (range: 4-91.2 months; interquartile range (IQR): 18.5-48months). The 3‑year BFS was 92%. Atotal of 12(16.2%) biochemical failures were reported. In univariate analysis, an mEPE score of 5, the delivered total radiation dose (35 Gy vs. 36.25 Gy), and aprostate-specific antigen (PSA) nadir >1 ng/ml were associated with lower BFS (mEPE-BFS: p < 0.001, total radiation dose-BFS: p = 0.04, PSAnadir-BFS: p =< 0.001). Patients diagnosed with intermediate-risk prostate cancer with ahigh mEPE score are more likely to experience biochemical failure after SBRT. Treatment intensification measures, such as administration of concomitant ADT, should be considered.