title: Image-guided radiotherapy for liver cancer using respiratory-correlated computed tomography and cone-beam computed tomography.
abstract: OBJECTIVE
  To evaluate a novel four-dimensional (4D) image-guided radiotherapy (IGRT) technique in stereotactic body RT for liver tumors.
  
  
  METHODS
  For 11 patients with 13 intrahepatic tumors, a respiratory-correlated 4D computed tomography (CT) scan was acquired at treatment planning. The target was defined using CT series reconstructed at end-inhalation and end-exhalation. The liver was delineated on these two CT series and served as a reference for image guidance. A cone-beam CT scan was acquired after patient positioning; the blurred diaphragm dome was interpreted as a probability density function showing the motion range of the liver. Manual contour matching of the liver structures from the planning 4D CT scan with the cone-beam CT scan was performed. Inter- and intrafractional uncertainties of target position and motion range were evaluated, and interobserver variability of the 4D-IGRT technique was tested.
  
  
  RESULTS
  The workflow of 4D-IGRT was successfully practiced in all patients. The absolute error in the liver position and error in relation to the bony anatomy was 8 +/- 4 mm and 5 +/- 2 mm (three-dimensional vector), respectively. Margins of 4-6 mm were calculated for compensation of the intrafractional drifts of the liver. The motion range of the diaphragm dome was reproducible within 5 mm for 11 of 13 lesions, and the interobserver variability of the 4D-IGRT technique was small (standard deviation, 1.5 mm). In 4 patients, the position of the intrahepatic lesion was directly verified using a mobile in-room CT scanner after application of intravenous contrast.
  
  
  CONCLUSIONS
  The results of our study have shown that 4D image guidance using liver contour matching between respiratory-correlated CT and cone-beam CT scans increased the accuracy compared with stereotactic positioning and compared with IGRT without consideration of breathing motion.
authors.affiliation: Department of Radiation Oncology, Julius-Maximilians University, Wuerzburg, Germany. guckenberg_m@klinik.uni-wuerzburg.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Guckenberger
authors.forename: Reinhart A
authors.initials: RA
authors.lastname: Sweeney
authors.forename: Juergen
authors.initials: J
authors.lastname: Wilbert
authors.forename: Thomas
authors.initials: T
authors.lastname: Krieger
authors.forename: Anne
authors.initials: A
authors.lastname: Richter
authors.forename: Kurt
authors.initials: K
authors.lastname: Baier
authors.forename: Gerd
authors.initials: G
authors.lastname: Mueller
authors.forename: Otto
authors.initials: O
authors.lastname: Sauer
authors.forename: Michael
authors.initials: M
authors.lastname: Flentje
mesh_terms: D000328:Adult; D000368:Aged; D006528:Carcinoma, Hepatocellular / Q000000981:diagnostic imaging / Q000532:radiotherapy; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000556:secondary; D008297:Male; D008875:Middle Aged; D009068:Movement; D015588:Observer Variation; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D012119:Respiration; D013238:Stereotaxic Techniques