S1168
Clinical - Urology
ESTRO 2026
Thomas E Cowling 2 , Jan van der Meulen 2 , Noel Clarke 3 , Alison Tree 4 , Ajay Aggarwal 2 1 National Cancer Audit Collaborating Centre, Royal College of Surgeons of England, London, United Kingdom. 2 Department of Health Services Research & Policy, , London School of Hygiene & Tropical Medicine, London, United Kingdom. 3 Department of Urology, The Christie and Salford Royal NHS Trusts, Manchester, United Kingdom. 4 Department of Oncology, The Royal Marsden NHS Foundation Trust, London, United Kingdom Purpose/Objective: The PACE B and HYPO-RT study have established stereotactic body radiotherapy (SBRT) for the radical treatment of localised prostate cancer as an international standard of care. Although the trials have demonstrated excellent disease control, evidence regarding treatment-related adverse events in routine clinical practice across a wide unselected demographic group remains limited. This study compared genitourinary (GU) and gastrointestinal (GI) adverse events following SBRT with moderately hypofractionated and conventionally fractionated radiotherapy across a national contemporary cohort. Material/Methods: This population-based study used cancer registry and administrative datasets to include all men who received radical radiotherapy for prostate cancer in England (n=56 centres) between 2018 and 2023. Modal dose regimens were: 36 Gy in 5 fractions (SBRT), 60 Gy in 20 fractions (moderate hypofractionation) and 74 Gy in 37 fractions (conventional). Baseline characteristics were compared across treatment groups. The 18-month cumulative incidences of significant (Grade 3 and Grade 2 needing intervention) GI and GU adverse events were estimated. Multivariable Cox proportional hazards regression was used to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for adverse event outcomes. Statistical significance was defined as p<0.05. Results: Among 67,764 men, 2,137 received SBRT, 54,780 moderate hypofractionation and 10,847 conventional fractionation. At 18 months, the cumulative incidence of GU adverse events was 4.8%, 3.1% and 3.4%, respectively, while the cumulative incidence of GI adverse events was 6.6%, 6.1% and 7.1%, respectively. Adjusted GU adverse events risk was higher following SBRT (adjusted HR 1.58, 95% CI 1.25– 1.84; p<0.01), compared to moderately hypofractionated radiotherapy. GI adverse event risk was similar between SBRT and moderate hypofractionation (adjusted HR 1.03, 95% CI 0.90–1.18; p=0.67). Further evaluation of the GU adverse events showed that the most common causes were other specific disorders of bladder (including irradiation
total dose of 36.25 Gy/5 fractions. Radiomics features were extracted using Matlab V.24 (MathWorks 2024, Natick, Massachusetts). For each patient 137 3D texture features, 56 3D Intensity histogram features and 26 3D shape features from the MR images of fraction 1 and 5 of the radiation course. The changes in radiomics Features (Delta Radiomics) were then correlated with the nadir PSA level and time to nadir Results: The median Nadir PSA was 0.5 ng/ml (range, 0.00 – 4.2). The median time to nadir was 12.08 months (range, 303 – 35.7). The skewness of the Texture features and the 3D shape features curves were significantly correlated with the time to nadir PSA (p 0.038 and 0.027 respectively). Two of the Texture features were significantly correlated with the post treatment PSA nadir level (Large Zone Low Gray Level, p 0.025 and High Dependence High Gray Level, p 0.022). Four of the Intensity Histogram features were significantly correlated with the PSA nadir (Median Discretised Intensity, p 0.036, Intensity Histogram Mode, p 0.003, Minimum Histogram Gradient, p 0.032, Minimum Histogram Gradient Intensity, p 0.009) Conclusion: Nadir PSA and time to nadir appear to be influenced by partly overlapping but mostly distinct radiomics features. Quantitative MRgRT image analysis can provide predictors of post treatment PSA Kinetics in prostate cancer patients, offering an innovative and personalized management approach References: 1. Wallace T, Torre T, Grob M, Yu J, Avital I, Brücher B et al (2014) Current approaches, challenges and future directions for monitoring treatment response in prostate cancer.J Cancer 5(1):32. Avanzo M, Wei L, Stancanello J, Vallières M, Rao A, Morin O, et al. Machine and deep learning methods for radiomics. Med Phys. 2020;47(5):185–2023. Sushentsev N, Rundo L, Blyuss O, Nazarenko T, Suvorov A, Gnanapragasam VJ, Sala E, Barrett T. Comparative performance of MRI- derived PRECISE scores and delta-radiomics models for the prediction of prostate cancer progression in patients on active surveillance. Eur Radiol. 2022 Jan;32(1):680-689 Keywords: Adaptive Radiotherapy, Radiomics, MRLinac Poster Discussion 1085 Treatment-Related Adverse Events Using Stereotactic Body Radiotherapy for Localised Prostate Cancer: A National Population-Based Study Joanna Dodkins 1 , Adrian Cook 1 , Emily Mayne 1 , Marina Parry 1 , Matthew G Parry 1 , Arjun Nathan 1 , Justin Liu 1 ,
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