title: 6D image guidance for spinal non-invasive stereotactic body radiation therapy: Comparison between ExacTrac X-ray 6D with kilo-voltage cone-beam CT.
abstract: OBJECTIVE
  To investigate setup discrepancies measured with ExacTrac X-ray 6 degree-of-freedom (6D) and cone-beam computed tomography (CBCT) for patients under treatments of stereotactic body radiation therapy (SBRT).
  
  
  METHODS
  In this work, phantom and patient studies were performed. In the phantom studies, an anthropomorphic phantom was placed with pre-defined positions, and imaged with ExacTrac X-ray 6D and CBCT to test the accuracy of the imaging systems. In the patient studies, 16 spinal SBRT patient cases were retrospectively analyzed. The patients were initially positioned in customized immobilization cradles and then aligned with ExacTrac X-ray 6D and CBCT. The setup discrepancies were computed and quantitatively analyzed.
  
  
  RESULTS
  This study indicates modest discrepancies between ExacTrac X-ray 6D and CBCT with spinal SBRT. The phantom experiments showed that translational and rotational discrepancies in root-mean-square (RMS) between ExacTrac X-ray 6D and CBCT were, respectively, <1.0mm and <1 degrees . In the retrospective patient studies, translational and rotational discrepancies in RMS between ExacTrac X-ray 6D and CBCT were <2.0mm and <1.5 degrees .
  
  
  CONCLUSIONS
  ExacTrac X-ray 6D represents a potential alternative to CBCT; however, pre-caution should be taken when only ExacTrac X-ray 6D is used to guide SBRT with small setup margins.
authors.affiliation: Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA. zheng.chang@duke.edu
authors.forename: Zheng
authors.initials: Z
authors.lastname: Chang
authors.forename: Zhiheng
authors.initials: Z
authors.lastname: Wang
authors.forename: Jinli
authors.initials: J
authors.lastname: Ma
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: O'Daniel
authors.forename: John
authors.initials: J
authors.lastname: Kirkpatrick
authors.forename: Fang-Fang
authors.initials: FF
authors.lastname: Yin
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D019047:Phantoms, Imaging; D016634:Radiosurgery / Q000379:methods*; D012189:Retrospective Studies; D013125:Spinal Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery*