title: On-board imaging validation of optically guided stereotactic radiosurgery positioning system for conventionally fractionated radiotherapy for paranasal sinus and skull base cancer.
abstract: OBJECTIVE
  To evaluate the positioning accuracy of an optical positioning system for stereotactic radiosurgery in a pilot experience of optically guided, conventionally fractionated, radiotherapy for paranasal sinus and skull base tumors.
  
  
  METHODS
  Before each daily radiotherapy session, the positioning of 28 patients was set up using an optical positioning system. After this initial setup, the patients underwent standard on-board imaging that included daily orthogonal kilovoltage images and weekly cone beam computed tomography scans. Daily translational shifts were made after comparing the on-board images with the treatment planning computed tomography scans. These daily translational shifts represented the daily positional error in the optical tracking system and were recorded during the treatment course. For 13 patients treated with smaller fields, a three-degree of freedom (3DOF) head positioner was used for more accurate setup.
  
  
  RESULTS
  The mean positional error for the optically guided system in patients with and without the 3DOF head positioner was 1.4 ± 1.1 mm and 3.9 ± 1.6 mm, respectively (p <.0001). The mean positional error drifted 0.11 mm/wk upward during the treatment course for patients using the 3DOF head positioner (p = .057). No positional drift was observed in the patients without the 3DOF head positioner.
  
  
  CONCLUSIONS
  Our initial clinical experience with optically guided head-and-neck fractionated radiotherapy was promising and demonstrated clinical feasibility. The optically guided setup was especially useful when used in conjunction with the 3DOF head positioner and when it was recalibrated to the shifts using the weekly portal images.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305-5847, USA.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Maxim
authors.forename: Billy W
authors.initials: BW
authors.lastname: Loo
authors.forename: James D
authors.initials: JD
authors.lastname: Murphy
authors.forename: Karen P M
authors.initials: KP
authors.lastname: Chu
authors.forename: Annie
authors.initials: A
authors.lastname: Hsu
authors.forename: Quynh-Thu
authors.initials: QT
authors.lastname: Le
mesh_terms: D000328:Adult; D000368:Aged; D054893:Cone-Beam Computed Tomography / Q000379:methods; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D010255:Paranasal Sinus Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D056888:Patient Positioning / Q000379:methods*; D010865:Pilot Projects; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods*; D061106:Radiotherapy Setup Errors; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012189:Retrospective Studies; D019292:Skull Base Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D055815:Young Adult