ESTRO 2025 - Abstract Book

S1947

Clinical - Urology

ESTRO 2025

disease-free survival (DFS). For distant metastases-free survival (DMFS) and overall survival (OS) no significant increase was found. Here we present updated results at ten-year follow-up.

Material/Methods: We recruited 571 patients with intermediate- and high-risk prostate cancer in the phase III multicenter randomized controlled FLAME trial (NCT01168479). Patients were randomized between the standard arm (77 Gy in 35 fractions) and the focal boost arm (standard treatment + focal boost of up to 95 Gy to the MRI-visible tumor(s)). Follow-up data was collected by all four participating centers for up to ten years, including prostate specific antigen (PSA) values and biochemical (PSA nadir + 2ng/mL), local, lymph node and/or distant metastatic failure. Information on patient mortality and cause of death was recorded. Kaplan-Meier analysis was used to assess survival outcomes (bDFS, DFS, DMFS and OS). Differences between arms were evaluated with a log-rank test (significance for p<0.05). Cox regression was performed to derive the hazard ratio (HR) for 10-year bDFS. Additionally, dose-response curves were created to account for dose heterogeneity in the study arm caused by prioritization of the organs-at-risk constraints over the focal boost dose. Results: The median follow-up was 106 months. The 10-year bDFS was 86% (33 events; 95% CI: 82%-91%) in the focal boost arm vs. 71% (70 events; 95% CI: 65%-77%) in the standard arm (log-rank test p<0.0001, Figure 1). The HR of the study arm compared to the standard arm was 0.40 (95% CI: 0.27-0.61; p<0.001). The 10-year DFS difference was statistically significant (log-rank test p<0.001) with 81% (43 events; 95% CI:76%-87%) in the focal boost arm vs. 66% (80 events; 95% CI: 61%-73%) in the standard arm. The DMFS was 87% in the focal boost arm compared to 82% in the standard arm (log-rank test p=0.18). Although this was not statistically significant, we observed a dose-response relation also for this outcome (Figure 2). The OS was not statistically significant (log-rank test p=0.73).