TH-CD-202-09: Free-Breathing Proton MRI Functional Lung Avoidance Maps to Guide Radiation Therapy

Abstract

Purpose: Pulmonary functional MRI using inhaled gas contrast agents was previously investigated as a way to identify well-functioning lung in patients with NSCLC who are clinical candidates for radiotherapy. Hyperpolarized noble-gas (3He and 129Xe) MRI has also been optimized to measure functional lung information, but for a number of reasons, the clinical translation of this approach to guide radiotherapy planning has been limited. As an alternative, free-breathing pulmonary 1H MRI using clinically available MRI systems and pulse sequences provides a non-contrast-enhanced method to generate both ventilation and perfusion maps. Free-breathing 1H MRI exploits non-rigid registration and Fourier decomposition of MRI signal intensity differences (Bauman et al., MRM, 2009) that may be generated during normal tidal breathing. Here, our objective was to generate free-breathing 1H MRI ventilation and lung function avoidance maps in patients with NSCLC as a way to guide radiation therapy planning. Methods: Stage IIIA/IIIB NSCLC patients (n=8, 68±9yr) provided written informed consent to a randomized controlled clinical trial (https://clinicaltrials.gov/ct2/show/NCT02002052) that aimed to compare outcomes related to image-guided versus conventional radiation therapy planning. Hyperpolarized 3He/129Xe and dynamic free tidal-breathing 1H MRI were acquired as previously described (Capaldi et al., Acad Radiol, 2015). Non-rigid registration was performed using the modality-independent-neighbourhood-descriptor (MIND) deformable approach (Heinrich et al., Med Image Anal, 2012). Ventilation-defect-percent (3He:VDPHe, 129Xe:VDPXe, Free-breathing-1H:VDPFB) and the corresponding ventilation maps were compared using Pearson correlation coefficients (r) and the Dice similarity coefficient (DSC). Results: VDPFB was significantly related to VDPHe (r=.71; p=.04) and VDPXe (r=.80; p=.01) and there were also strong spatial relationships (DSCHe/DSCXe=89±3%/77±11%). Conclusion: In this proof of concept study in NSCLC patients, free-breathing 1H MRI ventilation defects were quantitatively and spatially related to inhaled-noble-gas MRI ventilation defects. Free-breathing 1H MRI measures lung function/ventilation that can be used to optimize radiotherapy planning in NSCLC patients.