S1187
Clinical - Urology
ESTRO 2026
excellent tumor control for localized prostate cancer but remains associated with treatment-related urinary and sexual morbidity. Functional pelvic substructures, such as the bladder trigone, urogenital diaphragm, neurovascular bundles (NVB), penile bulb (PB), internal pudendal arteries (IPA), and crura, are increasingly recognized as potential mediators of these toxicities. However, dose-effect relationships remain poorly defined, particularly in the setting of single-dose ablative radiotherapy (SDRT). This post hoc analysis of the prospective ABRUPT trial (NCT04831983) examined the relationship between substructure dose and treatment-related side effects. Material/Methods: Thirty patients treated with SDRT and catheter-based bladder filling were analyzed. Functional substructures were contoured by a single radiation oncologist with >20 years of experience, and maximum and mean doses were extracted from planning dose-volume histograms. Toxicity was assessed using CTCAE and patient-reported outcome (PRO) instruments. Logistic regression, Wilcoxon-Mann-Whitney, and ROC analyses were performed to identify dose–toxicity relationships and predictive thresholds, with cross- validation for robustness. Results: The minimum follow-up duration was 24 months (range, 24–48 months). Thirteen patients (43%) experienced physician-reported late urinary toxicity (5 G2, 8 G1), while 19 patients (63%) showed a clinically meaningful deterioration in the urinary domain of the EORTC QLQ-PR25 questionnaire. Late urinary toxicity significantly correlated with bladder trigone dose, with a D1cc ≥ 20.3 Gy predicting urinary dysfunction (cross- validated AUC = 0.80; PPV = 64.3%; NPV = 75.0%), consistent across physician- and patient-reported endpoints. Larger bladder volumes (>166.8 cc) were also associated with worse urinary PRO outcomes (P = 0.030). Twenty-two patients (73%) recovered their testosterone level at the time of analysis, with a median time-to-testosterone recovery from ADT completion of 10 months. A total of 3 physician- reported erectile dysfunction events (14%) were recorded after testosterone recovery. Erectile dysfunction correlated with NVB D0.035cc ≥ 23.6 Gy (AUC = 0.98; PPV = 66.7%; NPV = 94.7%). Trends toward higher IPA and crura doses were observed in patients with sexual dysfunction, while no clear dose- response relationship was identified for PB.
Conclusion: This first analysis of functional substructures in SDRT identifies the bladder trigone and NVB as exploratory but suggestive predictors of urinary and sexual morbidity. Incorporating substructure-sparing strategies into treatment planning could improve functional preservation and reduce late morbidity. Prospective validation in larger cohorts is warranted. Keywords: Substructures, Single-Fraction, Dose Sparing ¿Is online adaptive radiotherapy safe? Acute and late genitourinary and gastrointestinal toxicity with or without BT boost in prostate cancer. Darwin Pozo, Marta Barrado, Ignacio Visus, Lucia Biscari, Nuria Bulto, Sonia Flamarique, Libe Amondarain, Sara Lopez, Cristina Felipe, Laura Casana, Rodrigo Astudillo, Naiara Fuentemilla, Ana Marza, Paula Calvo, Elena Villafranca Integrated Functional Unit of Radiotherapy, University Hospital of Navarra, Pamplona, Spain Purpose/Objective: Online adaptive radiotherapy (oART) aims to account for daily anatomical variability and may improve tumor coverage and reduce dose to organs at risk. The addition of a brachytherapy boost could further modulate dose distribution and toxicity. We evaluated whether oART combined with brachytherapy (oART+BT) is associated with lower acute or chronic GU/GI toxicity compared with oART alone. Material/Methods: Digital Poster 1663 Retrospective analysis of an institutional cohort of 93 patients treated with oART for prostate cancer; 6 patients treated with SBRT were excluded from the primary analysis. The comparison included 39 patients in the oART+BT group (Group 2) and 48 patients in the oART-only group (Group 3). Primary endpoints were rates of acute and chronic genitourinary (GU) and gastrointestinal (GI) toxicity (categorical variables
Made with FlippingBook - Share PDF online