ESTRO 2025 - Abstract Book

S1884

Clinical - Urology

ESTRO 2025

Purpose/Objective:

To compare the treatment outcomes and toxicity of radiotherapy (RT) at a dose of 78 Gy administered in 39 fractions, with or without 86 Gy focal boost (FB) to intraprostatic lesions (IPL), using the simultaneous integrated boost (SIB) technique in patients with prostate cancer (PCa). Material/Methods: A total of 712 patients were initially included, with 592 remaining after propensity score matching (PSM). Key outcomes included biochemical disease-free survival (bDFS), prostate cancer-specific survival (PCSS), and treatment related toxicities Results: A total of 592 patients were analyzed: 289 (48.8%) underwent SIB, and 303 (51.2%) did not. The median age of the cohort was 69 years (range: 47 – 87 years), with a median serum PSA value of 15.2 ng/mL (range: 1.2 – 382.4 ng/mL). Most patients had tumors classified as ISUP grade ≤ 3 (77.9%) and were at an early clinical T stage (72.3%). Additionally, 44.8% of patients were diagnosed with intermediate-risk disease, while 55.2% had high-risk disease. With a median follow-up of 9.5 years, the 10-year bDFS and PCSS rates were 84.3% and 91.8%, respectively. Univariate analysis identified serum PSA level, clinical T stage, ISUP grade, and risk group as significant prognostic factors for bDFS and PCSS. Patients who underwent SIB had a higher 10-year PCSS (96.7% vs. 86.7%; p=0.001), but no significant difference in bDFS (86.9% vs. 82.1%, p=0.29) (Figure 1). Multivariate analysis showed elevated PSA [HR=3.20 (1.54 – 6.64); p=0.002] and higher ISUP grade [HR=2.61 (1.50 – 4.54); p<0.001] as independent predictors of worse outcomes, while advanced T stage impacted bDFS negatively. The absence of FB to IPL [HR=2.46 (1.10 – 5.49); p=0.03] correlated with poorer PCSS. The 5-year LR rates were significantly lower in patients treated with the SIB technique compared to those who did not receive SIB (0.4% vs. 1.5%; p < 0.001) (Figure 3A). However, there was no significant difference in 5-year DM rates between the two treatment groups (11.0% vs. 14.6%; p=0.41). In regression analysis, the use of FB to IPL was the only factor that significantly improved local control (HR = 0.12, [95% CI, 0.03 – 0.51], p < 0.008). The use of FB to IPL improved local control without significantly increasing GI and GU toxicities.