ESTRO 2021 Abstract Book

S1524

ESTRO 2021

Conclusion An RBE-LETd relation is shown for the biological response of parotid glands as measured using PSMA-PET. This study shows PSMA-PET can be used to investigate the spatial distribution of RBE of the salivary glands in a clinical setting. Such studies can provide much needed clinical validation of RBE models required for clinical use. Following the methodology described above in a higher sample size and/or more time points may result in an RBE model fitted to clinically relevant data. PO-1798 Impact of inter-observer variability on MRI radiomic features in bladder cancer T. Elumalai 1 , Y.P. Song 2 , H. Mistry 3 , M. Dubec 4 , S. Jackson 4 , M.V. Herk 5 , P. Hoskin 5 , A. Choudhury 5 , A. McWilliam 5 1 The Christie NHS foundation trust, Clinical Oncology, Manchester, United Kingdom; 2 The Christie NHS foundation trust, Clinical oncology, Manchester, United Kingdom; 3 The University of manchester, Division of Cancer Sciences, Faculty of Biology, Medicine and Health, , Manchester, United Kingdom; 4 The Christie NHS foundation trust, Department of medical physics, Manchester, United Kingdom; 5 University of Manchester, Division of Cancer Sciences, Faculty of Biology, Medicine and Health, Manchester, United Kingdom Purpose or Objective Muscle-invasive bladder cancer (MIBC) can be radically treated with either surgery or radiotherapy. Regardless of treatment, overall 5-year survival remains poor with 1 in 2 patients dying of disease. Improved patient stratification is needed, identifying those who respond better to radiotherapy. Using imaging biomarkers from on-treatment MRI such as radiomic features is one viable strategy. We aimed to identify MRI radiomic features robust for inter-observer variation in MIBC patients treated with chemo-radiotherapy and compare bladder wall (BW) and tumour bed (TB). Materials and Methods Ten eligible MIBC patients were recruited to an MRI imaging study while undergoing chemo-radiotherapy. All patients were treated with GemX (52.5 /20 fractions with Gemcitabine 100 mg/m2 weekly). Weekly scans were taken during treatment on a Siemens 1.5T diagnostic MRI scanner. BW and TB were segmented as the region of interests on the weekly T2-weighted MRI images by two clinical oncologists to evaluate inter- observer variability. In total, 40 MRI images were available to extract features using pyRadiomics (v3.0.1). Robustness to inter-observer variation was assessed using the intraclass correlation coefficient ( ICC). Distribution of features in BW and TB was compared using inter-quartile range.