S1288
Clinical - Urology
ESTRO 2026
assessed according to CTCAE v4.0, regardless of time of onset. Associations between treatment parameters and toxicity were evaluated using odds ratios (OR) and multivariate logistic regression analysis. Results: After a median follow-up of 25 months, maximal toxicity ≥ grade 2 was observed in 9.8% of patients. The Girona centre, which predominantly used higher fractionation (>2.5 Gy/fx), showed significantly higher rates of maximal toxicity (80.2% of all toxic cases; OR 7.45, p<0.001). Fraction doses ≥ 2.5 Gy/fx were strongly associated with increased toxicity (OR 5.00 [3.09–8.35], p<0.001). Conversely, regimens including HDR brachytherapy demonstrated the lowest rates of GU/GI toxicity (p<0.001). Pelvic irradiation, present in 22.8% of patients, did not independently increase toxicity when adjusted for fraction size and dose– volume parameters. Rectal and bladder dose–volume metrics (V60–V75 Gy) were significantly correlated with higher toxicity (p<0.001).
Conclusion: Daily CBCT-based oART and IGRT were both well tolerated, with low rates of high-grade acute toxicity. GI toxicities were more favourable with oART. Moreover, oART was associated with preservation of HRQoL, suggesting that adaptive workflows may translate into tangible patient-centered benefits during prostate radiotherapy. References: 1. Musoro JZ, Coens C, Sprangers MAG, Brandberg Y, Groenvold M, Flechtner HH, et al. Minimally important differences for interpreting EORTC QLQ-C30 change scores over time: a synthesis across 21 clinical trials involving nine different cancer types. Eur J Cancer. 2023 July;188:171–82. Keywords: PROMs, adaptive radiotherapy, prostate cancer Digital Poster 4159 Association between fractionation dose, treatment modality, and maximal toxicity in prostate radiotherapy: a two-centre comparative analysis Ana Boladeras 1 , Alvar Roselló 2 , Francisco Pino 1 , Josep Jové 3 , Ferran Ferrer 1 , Rafael Fuentes 2 , Monica Caro 3 , Carmen Auñon 2 , Nagore Garcia 1 , Ana Alvarez 3 , Guadalupe Molina 3 , Andrea Slocker 1 , Pablo Araguas 1 , Arancha Eraso 1 1 Radiation Oncology, Institut Català d'Oncologia, Barcelona, Spain. 2 Radiation Oncology, Institut Català d'Oncologia, Girona, Spain. 3 Radiation Oncology, Institut Català d'Oncologia, Badalona, Spain Purpose/Objective: To assess the relationship between fractionation dose, treatment modality, and the incidence of maximal genitourinary (GU) and gastrointestinal (GI) toxicity in prostate cancer patients treated with different planning strategies in two radiation oncology centres. Material/Methods: A retrospective analysis was performed including 876 patients treated between August 2005 and May 2022 with external beam radiotherapy (EBRT) or combined EBRT and high-dose-rate brachytherapy (HDR-BQT) at two institutions (Hospitalet and Girona). Fractionation schedules included conventional (1.8–2 Gy/fx), moderate hypofractionation (2.2–2.5 Gy/fx), and high fractionation ( ≥ 2.7–3 Gy/fx), with or without pelvic irradiation (22.8% of cases) and/or HDR brachytherapy boost (9–15 Gy). Maximal GU and GI toxicities were
Conclusion: Maximal GU and GI toxicity were significantly associated with fractionation dose and treatment modality. Higher fractionation (>2.5 Gy/fx) was linked to increased toxicity, while combined EBRT + HDR brachytherapy achieved dose escalation with lower toxicity. Pelvic irradiation showed no significant impact
when dosimetric factors were accounted for. Evaluating maximal rather than temporal (acute/chronic) toxicity offers a more reliable
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