title: Stereoscopic X-ray imaging, cone beam CT, and couch positioning in stereotactic radiotherapy of intracranial tumors: preliminary results from a cross-modality pilot installation.
abstract: BACKGROUND
  To assess the accuracy and precision of a fully integrated pilot installation of stereoscopic X-ray imaging and kV-CBCT for automatic couch positioning in stereotactic radiotherapy of intracranial tumors. Positioning errors as detected by stereoscopic X-ray imaging are compared to those by kV-CBCT (i.e. the accuracy of the new method is verified by the established method), and repeated X-ray images are compared (i.e. the precision of new method is determined intra-modally).
  
  
  METHODS
  Preliminary results are reported from a study with 32 patients with intracranial tumors. Patients were treated with stereotactic radiotherapy guided by stereoscopic X-ray imaging and kV-CBCT. Patient positioning was automatically corrected by a robotic couch. Cross-modal discrepancies in position detection were measured (N = 42). Intra-modal improvements after correction and re-verification by stereoscopic X-ray imaging were measured (N = 70). The accuracy and precision of stereoscopic X-ray imaging and the accuracy and precision of CBCT were confirmed in phantom measurements (N = 12 shifts of a ball bearing phantom, N = 24 shifts of a head phantom).
  
  
  RESULTS
  After correction based on stereoscopic X-ray imaging 95% of residual mean errors were below 0.4, 0.4, 0.5, and 0.7 mm (lateral, longitudinal, vertical, radial, respectively). Stereoscopic X-ray imaging and CBCT were in close agreement with an average discrepancy of 0.1, 0.5, 0.3 and 0.8 mm, respectively. 95% of discrepancies were below 0.8, 1.2, 1.0, and 1.4 mm, respectively. After correction and re-verification by stereoscopic X-ray imaging, the remaining intra-modal residual error was consistent with zero (p = 0.31, p = 0.48, p = 0.81 in lateral, longitudinal, and vertical direction; p-values from two-tailed t-test). The inherent technical accuracy and precision of stereoscopic X-ray imaging and the accuracy and precision of CBCT were found to be of the order of 0.1 mm in controlled phantom settings.
  
  
  CONCLUSIONS
  In a routine clinical setting, both stereoscopic X-ray imaging and CBCT were able to reduce positioning errors by an order of magnitude. The end-to-end precision of the system, measured from the discrepancy (mean) between ExacTrac and CBCT, in a clinical setting seems to be about 0.8 mm radially, including couch positioning. The precision (measured from repeatability of ExacTrac, intra-modal) was found to be about 0.7 mm radially in a clinical setting.
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Zollner
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Heinz
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Pitzler
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany.
authors.forename: Farkhad
authors.initials: F
authors.lastname: Manapov
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany.
authors.forename: Steffi
authors.initials: S
authors.lastname: Kantz
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany.
authors.forename: Maya Christine
authors.initials: MC
authors.lastname: Rottler
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Niyazi
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Ganswindt
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany.
authors.forename: Claus
authors.initials: C
authors.lastname: Belka
authors.affiliation: LMU Munich, Department of Radiation Oncology, Marchioninistraße 15, Munich, 81377, Germany. Hendrik.Ballhausen@med.uni-muenchen.de.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Ballhausen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D056888:Patient Positioning / Q000379:methods*; D011859:Radiography; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies
keywords: Cone beam computed tomography; Image guided radiotherapy; Intracranial tumors; Patient positioning; Radiosurgery; Stereoscopic X-ray imaging; Stereotactic radiotherapy