ESTRO 2025 - Abstract Book

S1532

Clinical – Mixed sites & palliation

ESTRO 2025

Kingdom. 3 Radiotherapy Related Research, The Christie NHS Foundation Trust, Manchester, United Kingdom. 4 Medical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom

Purpose/Objective: Sarcopenia describes decline in skeletal muscle (SM) quantity/quality, with reduced quality defined as increased intramuscular adipose tissue (IMAT). Both are linked to increased mortality in cancer patients (1, 2) . Prostate and lung cancer treatment is multi-modal, and patient-, disease- and treatment-related factors contribute to changes in muscle quantity/quality. We aimed to identify body composition factors associated with worse late radiotherapy related toxicity. Material/Methods: We obtained data including CT images and clinician-/patient-reported outcomes up to 24 months post-radiotherapy from the multicentre prospective REQUITE study for 1,760 and 529 patients with non-metastatic prostate and lung cancer respectively, treated with radiotherapy. Multiple imputation (10 imputations, 5 iterations) was used for missing data. In-house software segmented SM and IMAT at the L5 and T12 vertebra for prostate and lung patients respectively, and subcutaneous and visceral adipose tissue (SAT, VAT) at L5. SM, IMAT, SAT and VAT were normalised by height squared to give SM, IMAT, SAT and VAT indices. IMAT ratio was calculated by dividing IMAT area by combined SM and IMAT area. Late standardised total average toxicity (STAT) scores (>90 days) were calculated for both cohorts (3) . Lung, oesophageal, rectal, bladder and bowel CTCAE V4.0 toxicity endpoints were included. Linear regression (LR) and random forest (RF) models containing well known predictive factors were developed for late clinician-/patient-reported toxicity. Cohorts were split 80:20 into training and test datasets. Internal validation was performed using a 5-fold cross-validation on the training dataset. External validation was performed on the test dataset.

Results: