ESTRO 2025 - Abstract Book

S1885

Clinical - Urology

ESTRO 2025

Conclusion: Our study demonstrates that the SIB technique effectively improves PCSS in patients with localized prostate cancer without significantly increasing toxicity. These findings support the use of dose escalation targeting IPL as a safe strategy to enhance local control and patient outcomes.

Keywords: Prostate cancer, radiotherapy, SIB.

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Digital Poster Evaluating the Prognostic Impact of Apparent Diffusion Coefficient in Definitive Radiotherapy for Gleason Score 7 Prostate Cancer Patients Cem Onal 1,2 , Aysenur Elmali 2 , Gurcan Erbay 3 , Birhan Demirhan 4 , Ozan C Guler 1 1 Department of Radiation Oncology, Baskent Unversity Faculty of Medicine, Adana, Turkey. 2 Department of Radiation Oncology, Baskent Unversity Faculty of Medicine, Ankara, Turkey. 3 Department of Radiology, Baskent Unversity Faculty of Medicine, Adana, Turkey. 4 Division of Radiation Oncology, Iskenderun Gelisim Hospital, Hatay, Turkey Purpose/Objective: To investigate the utility of diffusion-weighted magnetic resonance imaging (DW-MRI) in evaluating Gleason score (GS) 7 tumors before definitive radiotherapy (RT) and to explore its association with clinicopathological factors and treatment outcomes. Material/Methods: Clinical data of 266 prostate cancer (PCa) patients with biopsy-confirmed GS 7 who underwent RT were retrospectively analyzed. Pre-treatment DW-MRI was utilized to measure apparent diffusion coefficient (ADC) values of primary tumors. Treatment outcomes, including biochemical disease-free survival (bDFS) and prostate cancer specific survival (PCSS), were assessed. Statistical analyses were conducted to determine the correlation between tumor ADC values, clinicopathological factors, and treatment outcomes. Results: There was a significant difference in the mean ADC values between the normal prostate gland and the prostate tumor (1.389±0.219 × 10 ˗ ³ mm²/sec vs. 0.724±0.154 × 10 ˗ ³ mm²/sec, p < 0.001). Tumors with a GS of 3+4 had significantly higher ADC values than those with a GS of 4+3 (0.746±0.150 vs. 0.702±0.157 × 10 ˗ ³ mm²/sec; p < 0.001). Median follow-up time was 8.6 years, and the 7-year rates for bDFS and PCSS were 89.1% and 95.3%, respectively. Lower tumor ADC values were significantly correlated with higher GS and increased risk of disease progression. Patients who experienced progression had lower primary tumor ADC values compared to those who did not progress (0.673±0.176 × 10 ˗ ³ mm²/sec vs. 0.733±0.150 × 10 ˗ ³ mm²/sec; p = 0.03). In the dose-response curve, we found a clear correlation between tumor ADC and disease progression for the whole group (p = 0.03) and for GS 3 + 4 tumors (p = 0.001), but not for GS 4 + 3 tumors (p = 0.98) (Figure 1). A primary tumor ADC cutoff value of 0.682 × 10 ˗ ³ mm²/sec was identified for predicting disease progression. Patients with higher ADC values exhibited significantly better 7-year bDFS rates (92.8% vs. 83.2%; p = 0.02). However, GS 4+3 tumors independently predicted poorer bDFS and PCSS outcomes. In the multivariable analysis, only GS 4+3 tumor was predictive for worse bDFS and PCSS.