The Impact of Real-Time MRI Radiology-Based Peer Review on Head and Neck Radiotherapy Target Volume Delineation

Abstract

<h3>Purpose/Objective(s)</h3> As part of the introduction of planning MRI into the Radiotherapy (RT) workflow of Head Neck (HN) patients, we included HN radiology peer review to optimize target delineation. We hypothesized that this would result in significant target volume changes. <h3>Materials/Methods</h3> Radical cases with a fused diagnostic or RT planning MRI were prospectively identified. Gross Tumor Volumes (GTV) defined by HN oncologists were reviewed and modified, where indicated, by a HN radiologist and labelled (GTVonc, GTVrad). Following peer review, clinical target volumes (CTVonc, CTVrad) were created by adding a 10mm isotropic margin to each GTV-tumor (GTVT) or GTV-nodal (GTVN), then edited off anatomical barriers. The rate of changes, anatomical patterns of change, and factors associated with volume discrepancy were prospectively recorded. Amended and original volumes were compared using Dice Similarity Coefficient (DSC), Jaccard Index (JI) and Hausdorff Distance (HD). ‘Major' changes were defined as: editing of GTV by ≥10mm, editing to avoid a GTV geographical miss, inclusion of suspicious nodes within the high-dose CTV, and retrospectively assessed. <h3>Results</h3> 50 cases were reviewed between April 2019 and March 2020; 76% of GTVTs (38/50) and 42.8% of GTVNs (18/42) were modified. 31 GTVTs and 10 GTVNs were available for conformity assessment. Volume changes and conformity results are described in Table 1. Despite high conformity indices, 54.8% of GTVT (17/31) and 70% of GTVN (7/10) changes were considered ‘major'. The most frequent anatomical patterns of change were: GTVT soft tissue changes (92.1%; 35/38), and GTVN identification of additional nodes (83.3%; 15/18). The commonest qualitative reason for modifications to any GTV (n=41) were: imaging misinterpretation (75.6%, 31), changes made after collaborative discussion (17%, 7), and use of diffusion-weighted sequences (17%, 7). <h3>Conclusion</h3> Small, albeit statistically significant, differences in volume size were found on both GTVT and CTVT. While conformity index measures such as DSC were acceptable, the modifications were categorized as a "major" qualitative change in two thirds of patients. This highlights the importance of expert HN radiologist peer review of target volumes.