title: Prospective comparison of computed tomography and magnetic resonance imaging for liver cancer delineation using deformable image registration.
abstract: OBJECTIVE
  The aim of this study was to compare magnetic resonance imaging (MRI) with computed tomography (CT) for liver cancer tumor definition for high-precision radiotherapy planning.
  
  
  METHODS
  Diagnostic quality MRI scans and triphasic CT scans, with the liver immobilized in exhale, were obtained at the time of radiation planning for 26 patients with unresectable liver metastases (n = 8), hepatocellular carcinoma (n = 10), and cholangiocarcinoma (n = 8). On the CT and MRI series best demonstrating the tumor, the liver and gross tumor volumes (GTVs) were contoured, and intrahepatic anatomic reference points were identified. Deformable registration was used to register the liver from the CT with that from the MRI.
  
  
  RESULTS
  A difference in the number of tumor foci was seen on CT vs. MRI in 5 patients with hepatocellular carcinoma: MRI showed more foci in 3 patients, CT in 2. After deformable registration of the livers, the population median of the average distance between the CT tumor surface and MRI tumor surface was 3.7 mm (2.2-21.3 mm). The median percentage of tumor surface area that differed by > or = 5 mm was 26% (1-86%). Median percentage concordance volumes were 81% (77-86%) in metastases, 77% (60-88%) in hepatocellular carcinoma and 64% (25-85%) in cholangiocarcinoma.
  
  
  CONCLUSIONS
  Differences between MRI-defined liver cancer GTVs and CT-defined GTVs can be substantial and are more common in primary liver cancer.
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Jon-Paul
authors.initials: JP
authors.lastname: Voroney
authors.forename: Kristy K
authors.initials: KK
authors.lastname: Brock
authors.forename: Cynthia
authors.initials: C
authors.lastname: Eccles
authors.forename: Masoom
authors.initials: M
authors.lastname: Haider
authors.forename: Laura A
authors.initials: LA
authors.lastname: Dawson
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy; D018281:Cholangiocarcinoma / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging / Q000473:pathology; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated; D014057:Tomography, X-Ray Computed / Q000379:methods*