Association of Radiation Facility Volume with Overall Survival in Patients with Very High-Risk Prostate Cancer Treated with Radiation and Androgen Deprivation Therapy

Studies suggest an association of treatment at high volume facilities with improved survival in cancer patients receiving surgery or radiation therapy. This association has not been studied in patients with very high-risk prostate cancer, who are treated using a multimodality approach that often requires specialized care with advanced diagnostic imaging, complex radiotherapeutic planning, and multidrug antiandrogen regimens. We used the National Cancer Database (NCDB) to study the association of radiation treatment facility volume (FV) with overall survival (OS).We selected for patients with very high risk, localized prostate cancer by NCCN criteria (cT3b-T4, primary Gleason pattern 5, >4 cores with grade group 4-5, and/or 2-3 high risk features). We included patients who received hormone therapy with either external beam radiation to a dose of ≥60 Gy or external beam radiation to a dose of ≥45 Gy combined with brachytherapy. Association of FV with OS was evaluated through a bias-adjusted log-rank test to identify the optimal cut point of FV for dichotomization. Kaplan-Meier curves were used to study the association of binary FV with overall survival (OS) with and without IPTW (inverse probability treatment weighting) balancing the following confounders: age, race, median income, education, insurance, academic treatment facility, Charlson comorbidity score, T stage, PSA, Gleason score, total radiation dose, year of diagnosis, and patient distance from treatment facility. Cox proportional hazards model was built using backward variable selection strategy (α of 0.05 for removal).We identified 25,219 very high-risk prostate cancer patients by NCCN criteria (median follow up 57.36 months; 95% CI 56.67 - 58.09) diagnosed between 2004 and 2015. High FV (n = 6,438) was associated with better OS on univariable analysis (hazard ratio [HR] = 0.81; 95% confidence interval [CI] 0.77 - 0.86; p < 0.001) and multivariable analysis (HR = 0.89; 95% CI 0.84 - 0.95; p < 0.001). Other factors associated with improved OS on multivariable analysis included younger age, non-white/black race, higher income, private insurance, academic/research treatment facility, lower comorbidity, lower T-stage, lower PSA, and lower Gleason score. After IPTW adjustment, high FV remained associated with better OS (HR = 0.90; 95% CI 0.85 - 0.95; p < 0.001).Patients with NCCN very high-risk prostate cancer treated at a radiation facility with high case volume had better OS than patients treated at a facility with low volume, after adjustment for confounders. This may suggest that for very high-risk patients, outcomes may be improved by the expertise and optimal multidisciplinary care that typically accompany high facility treatment volume.