ESTRO 2025 - Abstract Book

S1533

Clinical – Mixed sites & palliation

ESTRO 2025

There were 1,217 and 303 successful segmentations for prostate and lung cancer patients respectively. Figure 1. summarises model performance. R 2 indicates how well the independent variables explain the variance in the dependent variable, ranging from 0-1. R 2 values were generally low in test datasets. R 2 values were higher for RF models than LR models. Body composition variables were ranked as important predictive variables in all RF models, with greater influence than conventional measurements such as weight and BMI. Figure 2. shows variable importance for late clinician-reported toxicity in the prostate cohort. Conclusion: Low R 2 values indicate poor external validation, perhaps due to limited patient numbers, missing data or incorrect selection of predictor variables. However, body composition variables were important predictive variables for late clinician-/patient-reported radiotherapy-related toxicity. Streamlined body composition assessment in oncology patients may allow identification of patients at high risk of toxicity. These results will need to be validated in further cohorts. References: adults with solid tumours: A meta-analysis and systematic review. Eur J Cancer. 2016;57:58-67. 2. Aleixo GFP, Shachar SS, Nyrop KA, Muss HB, Malpica L, Williams GR. Myosteatosis and prognosis in cancer: Systematic review and meta-analysis. Critical Reviews in Oncology/Hematology. 2020;145:102839. 3. Barnett GC, West CM, Coles CE, Pharoah PD, Talbot CJ, Elliott RM, et al. Standardized Total Average Toxicity score: a scale- and grade-independent measure of late radiotherapy toxicity to facilitate pooling of data from different studies. Int J Radiat Oncol Biol Phys. 2012;82(3):1065-74. Digital Poster Stereotactic body radiotherapy without systemic therapy for oligometastatic cancer - a systematic review and meta-analysis Camilla von Wachter 1 , Ronja Zehnder 1 , Edward Christopher Dee 2 , Hanbo Chen 3 , Lizza Hendriks 4 , Jordi Remon 5 , Sarah Baker 6 , Michael Mayinger 1 , Mohammadmilad Ameri 7 , Nicolaus Andratschke 1 , Umberto Ricardi 8 , Robert Olson 6 , Arjun Sahgal 3 , Dirk De Ruysscher 9 , Daniel Gomez 2 , Puneeth Iyengar 2 , Matthias Guckenberger 1 , Jonas Willmann 1,2 1 Department of Radiation Oncology, University Hospital Zurich, University of Zurich, Zurich, Switzerland. 2 Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, USA. 3 Department of Radiation Oncology, Sunnybrook Odette Cancer Centre, Toronto, Canada. 4 Department of Pulmonary Diseases, GROW-Research Institute for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht, Netherlands. 5 Department of Cancer Medicine, Gustave Roussy, Villejuif, France. 6 Department of Radiation Oncology, University of British Columbia, British Columbia, Canada. 7 Department of Dermatology, University Hospital Zurich, University of Zurich, Zurich, Switzerland. 8 Department of Oncology, University of Turin, Keywords: Toxicity, Modelling, Body-composition 2833