THE POTENTIAL IMPACT OF CT-MRI MATCHING ON TUMOR VOLUME DELINEATION IN ADVANCED HEAD AND NECK-CANCER

Purpose: To study the potential impact of the combined use of CT and M RI scans on the Gross Tumor Volume (GTV) estimation and interobserver variation. Methods and Materials: Four observers outlined the GTV in s ix patients with advanced head and neck cancer on CT, axial MRI, and c oronal or sagittal MRI, The MRI scans were subsequently matched to the CT scan, The interobserver and interscan set variation were assessed in three dimensions. Results: The mean CT derived volume was a factor of 1.3 larger than the mean axial MRI volume, The range in volumes was larger for the CT than for the axial MRI volumes in five of the six c ases, The ratio of the scan set common (i.e., the volume common to all GTVs) and the scan set encompassing volume (i.e., the smallest volume encompassing all GTVs) was closer to one in MRI (0.3-0.6) than in CT (0.1-0.5), The rest volumes (i.e., the volume defined by one observer as GTV in one data set but not in the other data set) were never zero for CT vs. MRI nor for MRI vs, CT, In two cases the craniocaudal borde r was poorly recognized on the axial MRI but could be delineated with a good agreement between the observers in the coronal/sagittal MRI. Co nclusions: MRI-derived GTVs are smaller and have less interobserver va riation than CT-derived GTVs, CT and MRI are complementary in delineat ing the GTV, A coronal or sagittal MRI adds to a better GTV definition in the craniocaudal direction. (C) 1997 Elsevier Science Inc.