ESTRO 2023 - Abstract Book

S803

Monday 15 May 2023

ESTRO 2023

Conclusion All qMRI parameters, except f, demonstrated potential as biomarkers of treatment response. However, the kinetics and magnitude of qMRI parameter change after RT varied between patients treated with and without ADT. Although the effect of RT cannot be distinguished from ADT in DCE-derived parameters, a lack of change in these parameters could be associated with poorly or non-responding tumours with risk of recurrence. As such, in developing predictive models of treatment response, the effects of ADT need to be considered. MO-0955 Ventilation and perfusion imaging at a 0.35 T MR-Linac - feasibility and reproducibility study R. Klaar 1,2 , M. Rabe 3 , T. Gaass 1,2 , M.J. Schneider 1,2 , I. Benlala 1,2,4 , S. Corradini 3 , C. Eze 3 , C. Belka 3,5 , G. Landry 3 , C. Kurz 3 , J. Dinkel 1,2 1 University Hospital, LMU Munich, Department of Radiology, Munich, Germany; 2 Comprehensive Pneumology Center (CPC M), Member of the German Center for Lung Research (DZL), Munich, Germany; 3 University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany; 4 Univ. Bordeaux, INSERM, Centre de recherche Cardio-Thoracique de Bordeaux, U1045, F-33000 Bordeaux, France; 5 German Cancer Consortium (DKTK), Munich site, Munich, Germany Purpose or Objective MR-Linacs have opened up possibilities not only in terms of precise tumor tracking, dose delivery and adapted treatment planning, but also for functional lung imaging in the clinical workflow for lung cancer treatment response monitoring without prolonging treatments. Non-uniform Fourier Decomposition (NuFD) is one of the techniques developed for non contrast enhanced lung MRI at 1.5 T and allows to assess ventilation (V) and perfusion (Q). Since low-field MRI has been shown to be advantageous for lung imaging due to low susceptibility artefacts, we aim at demonstrating the feasibility and potential of NuFD for a 0.35 T MR-Linac and propose two signal normalization strategies for enhancing reproducibility of the results in the presence of breathing amplitude variations. Materials and Methods Ten healthy volunteers (five female/male) were scanned with ethics approval at a 0.35 T MR-Linac (MRIdian, ViewRay Inc., Cleveland, Ohio) using an optimized balanced steady-state free precession (bSSFP) sequence with flip angle=70°, TR/TE=2.42/1.02 ms, FOV=500x500x20 mm ³ , matrix=128x128 and frame rate=3.68 images/s. Two coronal slices, referred to as ‘aorta’ and ‘lung’, were selected for each volunteer. Image series (240 images) were acquired in normal free-breathing with breaks inside and outside the scanner as well as in deep and shallow breathing. After image registration using ANTs and segmentation, the average lung signal was filtered into signals corresponding to V and Q. The NuFD was performed pixel-wise and V- and Q-maps were generated from the peak-value in the respective Fourier spectrum. For intra-volunteer V-map reproducibility, a normalization factor was defined based on the linear correlation of V-signal and diaphragm position of each scan as well as the diaphragm motion amplitude of the reference scan. This allows to correct the signal’s dependence on the diaphragm motion amplitude, which varies with breathing pattern. The second strategy normalizes the