title: The potential impact of CT-MRI matching on tumor volume delineation in advanced head and neck cancer.
abstract: OBJECTIVE
  To study the potential impact of the combined use of CT and MRI scans on the Gross Tumor Volume (GTV) estimation and interobserver variation.
  
  
  METHODS
  Four observers outlined the GTV in six patients with advanced head and neck cancer on CT, axial MRI, and coronal 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 cases. 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 border was poorly recognized on the axial MRI but could be delineated with a good agreement between the observers in the coronal/sagittal MRI.
  
  
  CONCLUSIONS
  MRI-derived GTVs are smaller and have less interobserver variation than CT-derived GTVs. CT and MRI are complementary in delineating the GTV. A coronal or sagittal MRI adds to a better GTV definition in the craniocaudal direction.
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Huis, Amsterdam.
authors.forename: C
authors.initials: C
authors.lastname: Rasch
authors.forename: R
authors.initials: R
authors.lastname: Keus
authors.forename: F A
authors.initials: FA
authors.lastname: Pameijer
authors.forename: W
authors.initials: W
authors.lastname: Koops
authors.forename: V
authors.initials: V
authors.lastname: de Ru
authors.forename: S
authors.initials: S
authors.lastname: Muller
authors.forename: A
authors.initials: A
authors.lastname: Touw
authors.forename: H
authors.initials: H
authors.lastname: Bartelink
authors.forename: M
authors.initials: M
authors.lastname: van Herk
authors.forename: J V
authors.initials: JV
authors.lastname: Lebesque
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000473:pathology; D000328:Adult; D000368:Aged; D005004:Ethmoid Bone / Q000000981:diagnostic imaging / Q000473:pathology; D005005:Ethmoid Sinus; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D006689:Hodgkin Disease / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008545:Melanoma / Q000000981:diagnostic imaging / Q000473:pathology; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D015588:Observer Variation; D009918:Orbital Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D010255:Paranasal Sinus Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D010307:Parotid Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D012888:Skull Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D014057:Tomography, X-Ray Computed