Prospective comparison of CT- and MRI-based tumor delineation based on intraoperative navigation and spatially annotated pathology in locally advanced midfacial squamous cell carcinoma

Introduction Precise tumor delineation is critical for navigation-guided surgery and radiotherapy (RT) in locally advanced midfacial squamous cell carcinoma (SCC). Contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) are both recommended for staging and provide complementary information. However, quantitative comparisons of CT- and MRI-based tumor contours remain scarce, while a spatial comparison with histopathological data has never been performed. Therefore, we prospectively compared gross tumor volumes (GTV) derived from CT and MRI before navigation-guided surgery and correlated the results with spatially annotated pathology. Methods This imaging sub-analysis was conducted within the prospective NAVIGATORR trial (NCT05671458). Fifteen patients with locally advanced midfacial SCC underwent contrast-enhanced CT and 1.5T or 3T MRI (T1w, T2w, DWI) for navigation-based surgery planning. Datasets were rigidly co-registered and an experienced radiologist independently contoured the GTV on CT and MRI while blinded to the other modality. Besides qualitative and volumetric evaluation, spatial agreement was assessed using the Dice similarity coefficient (DSC) and Hausdorff distance (HD). Tumor contours were correlated with spatially annotated intraoperative biopsy locations and histopathological results. Results Fifteen patients and 109 spatially annotated biopsy locations (19 tumor-positive) were analyzed. MRI was preferred for tumor delineation by the radiologist in all cases, with superior differentiation between tumor and mucosal swelling (73%) and improved soft tissue contrast (67%). MRI based GTVs were significantly larger than CT-based GTVs (median 28.3 ml vs. 16.8 ml; p = 0.02). DSC values demonstrated fair agreement with considerable heterogeneity (median 0.58; IQR 0.47-0.65), and median HD was 16 mm (IQR 12–27 mm). MRI-based contours encompassed numerically more tumor-positive biopsy locations than CT-based contours (6/19 vs. 1/19; clustered McNemar p = 0.20) while including fewer tumor-negative locations (7/90 vs. 10/90; p = 0.53). At patient level, at least one tumor-positive biopsy was located inside the contour in 3/8 (MRI) vs. 1/8 (CT) patients. Discussion GTV delineation differs substantially between MRI and CT in locally advanced midfacial SCC, and the two modalities provide complementary information. These exploratory findings support the complementary use of MRI and CT for tumor visualization. Clinical implications remain to be shown by the primary endpoint analysis of the NAVIGATORR trial.