title: Multiple breath-hold CBCT for online image guided radiotherapy of lung tumors: simulation with a dynamic phantom and first patient data.
abstract: OBJECTIVE
  Computer controlled breath-hold effectively reduces organ motion for image-guided precision radiotherapy of lung tumors. However, the acquisition time of 3D cone-beam-CT (CBCT) exceeds maximum breath-hold times. We have developed an approach enabling online verification using CBCT image acquisition with ABC®-based breath-hold.
  
  
  METHODS
  Patient CBCT images were acquired with ABC®-based repeat breath-hold. The clinical situation was also simulated with a Motion Phantom. Reconstruction of patient and phantom images with selection of free-breathing and breath-hold projections only was performed.
  
  
  RESULTS
  CBCT-imaging in repeat breath-hold resulted in a precisely spherical appearance of a tumor-mimicking structure in the phantom. A faint "ghost" structure (free-breathing phases) can be clearly discriminated. Mean percentage of patient breath-hold time was 66%. Reconstruction based on free-breathing-only shows blurring of both tumor and diaphragm, reconstruction based on breath-hold projections only resulted in sharp contours of the same structures. From the phantom experiments, a maximal repositioning error of 1mm in each direction can be estimated.
  
  
  CONCLUSIONS
  CBCT during repetitive breath hold provides reliable soft-tissue-based positioning. Fast 3D-imaging during one breath-hold is currently under development and has the potential to accelerate clinical linac-based volume imaging.
authors.affiliation: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1-3, Mannheim, Germany. judit.boda-heggemann@umm.de
authors.forename: Judit
authors.initials: J
authors.lastname: Boda-Heggemann
authors.forename: Jens
authors.initials: J
authors.lastname: Fleckenstein
authors.forename: Frank
authors.initials: F
authors.lastname: Lohr
authors.forename: Hansjörg
authors.initials: H
authors.lastname: Wertz
authors.forename: Mohammed
authors.initials: M
authors.lastname: Nachit
authors.forename: Manuel
authors.initials: M
authors.lastname: Blessing
authors.forename: Dzimitry
authors.initials: D
authors.lastname: Stsepankou
authors.forename: Iris
authors.initials: I
authors.lastname: Löb
authors.forename: Beate
authors.initials: B
authors.lastname: Küpper
authors.forename: Anthony
authors.initials: A
authors.lastname: Kavanagh
authors.forename: Vibeke N
authors.initials: VN
authors.lastname: Hansen
authors.forename: Michael
authors.initials: M
authors.lastname: Brada
authors.forename: Frederik
authors.initials: F
authors.lastname: Wenz
authors.forename: Helen
authors.initials: H
authors.lastname: McNair
mesh_terms: D003198:Computer Simulation; D054893:Cone-Beam Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011857:Radiographic Image Interpretation, Computer-Assisted; D012119:Respiration