title: Target localization of 3D versus 4D cone beam computed tomography in lipiodol-guided stereotactic radiotherapy of hepatocellular carcinomas.
abstract: BACKGROUND
  Aim of this study was to comparatively evaluate the accuracy of respiration-correlated (4D) and uncorrelated (3D) cone beam computed tomography (CBCT) in localizing lipiodolized hepatocellular carcinomas during stereotactic body radiotherapy (SBRT).
  
  
  METHODS
  4D-CBCT scans of eighteen HCCs were acquired during free-breathing SBRT following trans-arterial chemo-embolization (TACE) with lipiodol. Approximately 1320 x-ray projections per 4D-CBCT were collected and phase-sorted into ten bins. A 4D registration workflow was followed to register the reconstructed time-weighted average CBCT with the planning mid-ventilation (MidV) CT by an initial bone registration of the vertebrae and then tissue registration of the lipiodol. For comparison, projections of each 4D-CBCT were combined to synthesize 3D-CBCT without phase-sorting. Using the lipiodolized tumor, uncertainties of the treatment setup estimated from the absolute and relative lipiodol position to bone were analyzed separately for 4D- and 3D-CBCT.
  
  
  RESULTS
  Qualitatively, 3D-CBCT showed better lipiodol contrast than 4D-CBCT primarily because of a tenfold increase of projections used for reconstruction. Motion artifact was observed to subside in 4D-CBCT compared to 3D-CBCT. Group mean, systematic and random errors estimated from 4D- and 3D-CBCT agreed to within 1 mm in the cranio-caudal (CC) and 0.5 mm in the anterior-posterior (AP) and left-right (LR) directions. Systematic and random errors are largest in the CC direction, amounting to 4.7 mm and 3.7 mm from 3D-CBCT and 5.6 mm and 3.8 mm from 4D-CBCT, respectively. Safety margin calculated from 3D-CBCT and 4D-CBCT differed by 2.1, 0.1 and 0.0 mm in the CC, AP, and LR directions.
  
  
  CONCLUSIONS
  3D-CBCT is an adequate alternative to 4D-CBCT when lipoid is used for localizing HCC during free-breathing SBRT. Similar margins are anticipated with 3D- and 4D-CBCT.
authors.affiliation: Department of Radiation Oncology, University Medical Center Schleswig-Holstein, Kiel, Germany.
authors.forename: Mark
authors.identifier: http://orcid.org/0000-0002-0187-2703
authors.initials: M
authors.lastname: Chan
authors.affiliation: Department of Clinical Oncology, Tuen Mun Hospital, Hong Kong (S.A.R).|Department of Clinical Oncology, The University of Hong Kong, Hong Kong (S.A.R).|Department of Clinical Oncology, University of Hong Kong-Shenzhen Hospital, China.
authors.forename: Chi Leung
authors.initials: CL
authors.lastname: Chiang
authors.affiliation: Department of Clinical Oncology, Tuen Mun Hospital, Hong Kong (S.A.R).|Department of Clinical Oncology, The University of Hong Kong, Hong Kong (S.A.R).
authors.forename: Venus
authors.initials: V
authors.lastname: Lee
authors.affiliation: Department of Clinical Oncology, Tuen Mun Hospital, Hong Kong (S.A.R).
authors.forename: Steven
authors.initials: S
authors.lastname: Cheung
authors.affiliation: Department of Clinical Oncology, Tuen Mun Hospital, Hong Kong (S.A.R).
authors.forename: Ronnie
authors.initials: R
authors.lastname: Leung
authors.affiliation: Department of Clinical Oncology, Tuen Mun Hospital, Hong Kong (S.A.R).
authors.forename: Matthew
authors.initials: M
authors.lastname: Wong
authors.affiliation: Department of Clinical Oncology, Tuen Mun Hospital, Hong Kong (S.A.R).
authors.forename: Frankle
authors.initials: F
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, University Medical Center Schleswig-Holstein, Kiel, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Blanck
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D003287:Contrast Media / Q000008:administration & dosage*; D004998:Ethiodized Oil / Q000008:administration & dosage*; D006801:Humans; D008113:Liver Neoplasms / Q000532:radiotherapy*; D016634:Radiosurgery / Q000379:methods*
chemical_list: D003287:Contrast Media; D004998:Ethiodized Oil