ESTRO 2022 - Abstract Book

S1551

Abstract book

ESTRO 2022

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Conclusion Measuring ADC in bladder tumours on the MR-Linac is feasible. Difference between ADC all and ADC b100 likely reflects the intrinsic vascularity of bladder tumours and perfusion effects. Increase in ADC during treatment corresponds to CR seen on diagnostic MRI. Work is on-going to technically validate this imaging biomarker which may provide an early predictor of bladder cancer radiotherapy response.

PO-1750 Reproducibility of diffusion-weighted magnetic resonance imaging in head and neck cancer

J. Habrich 1 , V. Fritz 2 , S. Böke 3 , M. Nachbar 1 , K. Nikolaou 4 , F. Schick 2 , D. Zips 3 , D. Thorwarth 1

1 University Hospital and Medical Faculty, University of Tübingen, Section for Biomedical Physics, Department of Radiation Oncology, Tübingen, Germany; 2 University of Tübingen, Section for Experimental Radiology, Department of Diagnostic and Interventional Radiology, Tübingen, Germany; 3 University Hospital and Medical Faculty Tübingen, Department of Radiation Oncology, Tübingen, Germany; 4 University Hospital Tübingen, Department of Diagnostic and Interventional Radiology, Tübingen, Germany Purpose or Objective MR-Linacs (MRL) allow for sequential acquisition of functional magnetic resonance imaging (MRI) and therefrom derived quantitative imaging biomarkers such as apparent diffusion coefficients (ADC). The prognostic value of ADC derived from diffusion-weighted (DW)-MRI has been shown in offline studies in head and neck cancer (HNC), but for application at MRL, technical validation of DW sequences is required first. The aim of this study was to assess the reproducibility of ADC values derived from DW-MRI in HNC patients acquired with a hybrid 1.5 T MRL compared to a 3 T diagnostic scanner (DS). Materials and Methods Eight patients with locally advanced HNC were treated at the 1.5 T MRL (Unity, Elekta) and examined with DW-MRI at the MRL and additionally at a 3 T diagnostic scanner (Vida, Siemens) before (measurement 1) and during week 2 (measurement 2) of radiotherapy. ADC maps were calculated using a pixel-wise mono-exponential fit to signal amplitudes of the b150- and b500 images of the MRL and b200-, b500 and b1000 images of the 3 T scanner. Details of the sequence parameters are presented in Table 1. Mean ADC values and their relative differences were calculated for gross tumor volume (GTV),