Quality assurance assessment of Intra‐Acquisition Diffusion‐Weighted and T2‐Weighted magnetic resonance imaging registration and contour propagation for head and neck cancer radiotherapy

2 Abstract: 29 Background/Purpose: Adequate image registration of anatomic and functional MRI scans is 30 necessary for MR-guided head and neck cancer (HNC) adaptive radiotherapy planning. Despite 31 the quantitative capabilities of diffusion-weighted imaging (DWI) MRI for treatment plan 32 adaptation, geometric distortion remains a considerable limitation. Therefore, we systematically 33 investigated various deformable image registration (DIR) methods to co-register DWI and T2- 34 weighted (T2W) images. 35 36 Materials/Methods: We compared three commercial (ADMIRE, Velocity, Raystation) and three 37 open-source (Elastix with default settings [Elastix Default], Elastix with parameter set 23 [Elastix 38 23], Demons) post-acquisition DIR methods applied to T2W and DWI MRI images acquired 39 during the same imaging session in twenty immobilized HNC patients. In addition, we used the 40 non-registered images (None) as a control comparator. Ground truth segmentations of 41 radiotherapy structures (tumor and organs at risk) were generated by a physician expert on both 42 image sequences. For each registration approach, structures were propagated from T2W to 43 DWI images. These propagated structures were then compared with ground truth DWI 44 structures using the Dice similarity coefficient and mean surface distance. 45 46 Results: 19 left submandibular glands, 18 right submandibular glands, 20 left parotid glands, 20 47 right parotid glands, 20 spinal cords, and 12 tumors were delineated. Most DIR methods took < 48 30 seconds to execute per case, with the exception of Elastix 23 which took ~458 seconds to 49 execute per case. ADMIRE and Elastix 23 demonstrated improved performance over None for all 50 metrics and structures (Bonferroni-corrected p < 0.05), while the other methods did not. Moreover, 51 ADMIRE and Elastix 23 significantly improved performance in individual and pooled analysis 52 compared to all other methods. 53