ESTRO 2025 - Abstract Book

S1896

Clinical - Urology

ESTRO 2025

775

Digital Poster Association between short-term radiation-induced toxicity and oncological outcomes in high-risk prostate cancer Jenny Kahlmeter Brandell 1 , Antonios Valachis 1 , Henrik Ugge 2 , Daniel Smith 3 , Bengt Johansson 1 1 Department of Oncology, Faculty of Medicine and Health, Örebro University Hospital, Örebro University, Örebro, Sweden. 2 Department of Urology, Faculty of Medicine and Health, Örebro University Hospital, Örebro University, Örebro, Sweden. 3 Clinical Epidemiology and Biostatistics, School of Medical Sciences, Örebro University, Örebro, Sweden Purpose/Objective: Treatment-related toxicity is a well-known complication to radiotherapy, but its relation to oncologic outcomes has not been thoroughly investigated. Two studies on prostate cancer patients treated with external beam radiotherapy (EBRT) have demonstrated an inverse relationship between treatment-related symptoms and long-term prognosis [1, 2]. This retrospective cohort study aimed to explore the association between short-term genitourinary (GU) and gastrointestinal (GI) toxicity and oncological outcomes in high-risk prostate cancer patients treated with external beam radiotherapy (EBRT) alone or in combination with high-dose-rate brachytherapy (HDR-BT). Material/Methods: Patients with high-risk prostate cancer (cT1-3N0M0) treated with EBRT alone, or with HDR-BT boost, at Örebro University Hospital between 2008 and 2021 were identified from an institutional database and divided into two cohorts based on treatment modality: EBRT-only (66 Gy in 22 fractions) and EBRT+HDR-BT (42 Gy in 14 fractions + 14.5 Gy HDR-BT boost). Cumulative worst six months toxicity grade, measured at three weeks and six months, was categorized as follows: GU-low (grade 0-1), GU-high (grade 2+), GI-low (grade 0) and GI-high (grade 1+), respectively. Patients with baseline GU toxicity grade 2 and above were excluded from the GU-analyses. No information on baseline GI toxicity was available. Freedom from biochemical recurrence (FFBR), metastasis-free survival (MFS), prostate cancer-specific survival (PCSS), and overall survival (OS) were compared between the low- and high- toxicity groups for GU- and GI-toxicity, respectively, using the Kaplan-Meier method and Cox proportional hazards. The two treatment cohorts were analysed separately. Results: Baseline characteristics were similar between the low- and high-toxicity groups, except in the EBRT+HDR-BT-cohort, where the GU-high group was slightly older . There was a significant association between high GU-toxicity and inferior rates of FFBR (adjusted Hazard Ratio (aHR) = 2.57, 95% Confidence Interval (CI): 1.32-5.00) and MFS (aHR = 2.22, 95% CI: 1.21-4.07) in the EBRT-only cohort (Fig. 1), but not in the EBRT+HDR-BT cohort. No significant differences were found in FFBR, MFS, PCSS, or OS for GI toxicity. 5-year FFBR-, MFS-, PCSS- and OS rates along with aHR are summarized in Table 1.