ESTRO 2021 Abstract Book

S754

ESTRO 2021

compared the rate of utilization of radical local therapy before and after the publication of results from STAMPEDE (October 2018). Finally, we applied Cox multivariable regression to determine the association of local RT with OS. Results A total of 3556 patients met the eligibility criteria. Overall, 11% and 14% patients received local therapy within 6 and 12 months of diagnosis, respectively. When stratified according to publication of STAMPEDE data , 10% and 26% of patients received radical local therapy within 6 months of diagnosis in the pre-STAMPEDE vs. post-STAMPEDE era (p<0.0001). [WCJ1] On multinomial regression, there was significant geographic region in the use of definitive local therapy within 6 months of diagnosis (3% to 26%, p<0.0001) and within 12 months of diagnosis (9% to 34%, p<0.0001). [WCJ2] Additionally, patients with higher PSA values at diagnosis were less likely to receive local RT within 6 (Odd’s ratio [OR]: 0.83, 95% confidence intervals [CI]: 0.80-0.86) or 12 months (OR: 0.82, 95% CI: 0.79-0.86) of diagnosis. Receipt of local therapy within 6 or 12 months of diagnosis was associated with reduced risk of overall mortality [hazard ratio for £6 months cohort: 0.47 (95% CI: 0.28- 0.77) and £12 months cohort: 0.39 (95% CI: 0.26-0.59). Conclusion This population-based study showed a significant correlation between utilization of definitive local therapy in mCSPC and publication of the STAMPEDE trial. A significant geographic variation was noted in the adoption of local therapy in mCSPC. Acknowledging the limitations of the population-based study, receipt of local therapy was associated with a significant improvement in OS. PD-0912 Outcome of PSMA-PET/CT based salvage radiotherapy for nodal recurrence after radical prostatectomy P. Rogowski 1 , C. Trapp 2 , R. von Bestenbostel 1 , M. Li 1 , U. Ganswindt 3 , P. Bartenstein 4 , C. Stief 5 , C. Belka 1 , N. Schmidt-Hegemann 1 1 University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany; 2 University Hospital, LMU Munich, Department of Radiation Oncology, Mumich, Germany; 3 Medical University of Innsbruck, Department of Radiation Oncology, , Innsbruck, Austria; 4 University Hospital, LMU Munich, Department of Nuclear Medicine, Munich, Germany; 5 University Hospital, LMU Munich, Department of Urology, Munich, Germany Purpose or Objective Nodal recurrent prostate cancer represents a common state of disease, amenable to local therapy. Prostate- specific membrane antigen positron emission tomography/computed tomography (PSMA-PET/CT) detects prostate cancer recurrence at low PSA levels. Aim of this study was to evaluate the outcome of PSMA-PET/CT based salvage radiotherapy (sRT) for nodal recurrence. Materials and Methods A total of 100 consecutive patients treated with PSMA-PET/CT based sRT for nodal recurrence were retrospectively examined. Patients underwent PSMA-PET/CT scan due to biochemical persistence (bcP, 76%) or biochemical recurrence (bcR, 24%) after radical prostatectomy (RPE). Progression-free survival (PFS) defined as PSA < post-RT nadir + 0.2ng/ml was calculated using the Kaplan-Meier method and survival curves were compared using the log rank test. For multivariate analysis, cox regression analysis was performed (p < 0.05). Results Median follow-up was 37 months. Median PSA at PSMA-PET/CT was 1.65 ng/ml (range 0.1 - 40.1) in patients with bcP and 1.41 ng/ml (range 0.3 - 5.1) in patients with bcR. PSMA-PET/CT detected 1, 2 and 3 or more lymph node metastases in 35%, 23% and 42%, respectively. 83% had only pelvic, 2% had only paraaortic and 15% had pelvic and paraaortic lymph node metastases. Cumulatively, a total dose of 66 Gy (60 - 72 Gy) was delivered to the local macroscopic tumor or the prostatic fossa, 61.6 Gy (55 – 66 Gy) to PET-positive lymph nodes and 50.4 Gy (45 - 54 Gy) to the lymphatic pathways. Concomitant ADT was administered in 83% of patients. 1-,2- and 5-yr PFS was 79.9%, 68.2% and 54.7%, respectively. Concomitant ADT and a PSA value < 1 ng/ml before sRT were associated with better PFS in univariate and multivariate analysis. No such association was seen for number of affected lymph nodes nor localization (pelvic vs. paraaortic).