title: Phase-specific cone beam computed tomography reduces reconstructed volume loss of moving phantom.
abstract: OBJECTIVE
  The accurate volumetric calculation of moving targets/organs is required to use cone-beam computed tomography (CBCT) for replanning purposes. This study was aimed to correct the reconstructed volume losses of moving phantoms by phase-specific CBCT.
  
  
  METHODS
  Planning fan-beam CT (FBCT) of five hepatobiliary/gastrointestinal/pancreatic cancer patients were acquired under active breathing control and compared with free-breathing CBCT for kidney volumes. Three different-sized ball phantoms were scanned by FBCT and CBCT. Images were imported to a planning system to compare the reconstructed volumes. The phantoms were moved longitudinally on an oscillator with different amplitudes/frequencies. The phase-specific projections of CBCT for moving phantoms were selected for volume reconstruction.
  
  
  RESULTS
  The differences in reconstructed volumes of static small, medium, large phantoms between FBCT and CBCT were - 6.7%, - 2.3%, and - 2.0%, respectively. With amplitudes of 7.5-20 mm and frequencies of 8-16 oscillations/min, volume losses on CBCT were comparable with FBCT in large moving phantoms (range 9.1-27.2%). Amplitudes were more subject to volume losses than frequencies. On phase-specific CBCT, volume losses were reduced to 2.3-6.5% by reconstruction using 2-3 projections at end/midoscillation phase.
  
  
  CONCLUSIONS
  Amplitude had more impact than frequency on volume losses of moving phantoms on CBCT. Phase-specific CBCT reduced volume losses.
authors.affiliation: Division of Radiation Oncology, Department of Oncology, National Taiwan University Hospital, No. 7, Chung-Shan South Road, 10002, Taipei, Taiwan.
authors.forename: H-L
authors.initials: HL
authors.lastname: Chao
authors.forename: W-L
authors.initials: WL
authors.lastname: Chen
authors.forename: C-C
authors.initials: CC
authors.lastname: Hu
authors.forename: J-K
authors.initials: JK
authors.lastname: Wu
authors.forename: C-J
authors.initials: CJ
authors.lastname: Wu
authors.forename: J C-H
authors.initials: JC
authors.lastname: Cheng
mesh_terms: D016477:Artifacts; D001661:Biliary Tract Neoplasms / Q000532:radiotherapy; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005770:Gastrointestinal Neoplasms / Q000532:radiotherapy; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008113:Liver Neoplasms / Q000532:radiotherapy; D009369:Neoplasms / Q000532:radiotherapy*; D009929:Organ Size; D010190:Pancreatic Neoplasms / Q000532:radiotherapy; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D012680:Sensitivity and Specificity