S1180
Clinical - Urology
ESTRO 2026
patients with bPVRUV = 0 mL only 11% developed G2 acute GU toxicity, whilst among the 50 patients with bPVRUV > 0 mL 32% developed G2 acute GU toxicity.
Digital Poster Highlight 1286 post-void residual urinary volume is a predictor of acute urinary toxicity in stereotactic body radiation therapy for prostate cancer Enrico Raggi 1 , Carlo Furlan 2 , Margherita Crespi 3 , Vittorio Baggio 2 , Francesca Ciriello 1 , Olga Ionova 1 , Margherita Rotondi 1 , Anna Schiattarella 1 , Claudio Scoglio 1 , Alessandro Magli 1 1 SC Radioterapia, ASUGI, Trieste, Italy. 2 UOC Radioterapia, AULSS1, Belluno, Italy. 3 UOC Fisica Sanitaria, AULSS1, Belluno, Italy Purpose/Objective: stereotactic body radiation therapy (SBRT) has gained increasing use in the field of localized prostate cancer. Although it is well tolerated, a subgroup of patients still experience clinically relevant acute urinary morbidity. In this study we investigated the role of baseline post-void residual urinary volume (bPVRUV) as a possible predictor of acute genito-urinary (GU) toxicity. Material/Methods: one-hundred-forty patients given SBRT with 36.25 Gy in 5 fractions every other day for prostate adenocarcinoma were retrospectively evaluated. bPVRUV was assessed non-invasively with ultrasound. Before simulation, all patients underwent implantation of 3 intraprostatic fiducial markers for image-guided radiotherapy (IGRT). All patients were treated with Flattening Filter Free (FFF) volumetric modulated arc radiotherapy (VMAT). Image-guidance was done for every fraction with cone beam computed tomography (CBCT). Median age at diagnosis was 75 years (range 50-86). Median Karnofsky Performance status was 90 (range 80-100). bPVRUV, International Prostate Symptom Score (IPSS), age and whether androgen deprivation therapy had been prescribed were analysed as potential predictors for acute urinary morbidity. For statistical analysis, logistic regression models and Chi square test were used. Results: a correlation was demonstrated between bPVRUV > 0 mL and development of toxicity of any grade within the first week of SBRT (p=0.0370, Ors: 2.2615, 95% CI: 1.0433-4.9022), bPVRUV > 0 mL and development of toxicity of any grade at any time during treatment (p=0.0025, Ors: 2.9900, 95% CI: 1,4397-6.2099), bPVRUV > 0 mL and G2 acute GU toxicity (p=0.0066, Ors: 3.4290, 95% CI: 1.3656-8.6099); no correlation with acute urinary morbidity was demonstrated for age, IPSS and androgen deprivation therapy. At Chi squared test, an association was shown between an increase in IPSS at the end of SBRT exceeding 2 points (median value in the whole study population) when compared to baseline IPSS and both acute GU toxicity of any grade and G2 acute GU toxicity. Among the 90
Conclusion: our study highlights how bPVRUV is an indipendent predictor of acute GU toxicity in patients treated with SBRT for prostate cancer. Prospective confirmation could allow to introduce bPVRUV into nomogramms to calculate the risk of acute urinary morbidity and integrate bPVRUV into prevention protocols for subsets of patients at high risk of urinary toxicity. Keywords: prostate, stereotactic, toxicity Impact of interobserver variability in MRI-based urethra delineation on iso-toxic focal boost dose in prostate cancer radiotherapy Valeria Faccenda 1,2 , Cédric Draulans 3,4 , Floris J. Pos 5 , Constantinos Zamboglu 6,7 , Simon K.B. Spohn 6 , Jennifer Le Guévelou 8 , Nina Schmidt-Hegemann 9 , Astrid E. Persson 10,11 , Sophia L. Bürkle 6 , Casper Reijnen 12 , Binnaz Yasar 13 , Elena De Ponti 1 , Karin Haustermans 3,14 , Denis Panizza 1,2 , Stefano Arcangeli 2,15 1 Medical Physics, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy. 2 School of Medicine and Surgery, University of Milan Bicocca, Milan, Italy. 3 Department of Oncology, KU Leuven, Leuven, Belgium. Digital Poster 1377
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