title: A study of the accuracy of cyberknife spinal radiosurgery using skeletal structure tracking.
abstract: OBJECTIVE
  New technology has enabled the increasing use of radiosurgery to ablate spinal lesions. The first generation of the CyberKnife (Accuray, Inc., Sunnyvale, CA) image-guided radiosurgery system required implanted radiopaque markers (fiducials) to localize spinal targets. A recently developed and now commercially available spine tracking technology called Xsight (Accuray, Inc.) tracks skeletal structures and eliminates the need for implanted fiducials. The Xsight system localizes spinal targets by direct reference to the adjacent vertebral elements. This study sought to measure the accuracy of Xsight spine tracking and provide a qualitative assessment of overall system performance.
  
  
  METHODS
  Total system error, which is defined as the distance between the centroids of the planned and delivered dose distributions and represents all possible treatment planning and delivery errors, was measured using a realistic, anthropomorphic head-and-neck phantom. The Xsight tracking system error component of total system error was also computed by retrospectively analyzing image data obtained from eleven patients with a total of 44 implanted fiducials who underwent CyberKnife spinal radiosurgery.
  
  
  RESULTS
  The total system error of the Xsight targeting technology was measured to be 0.61 mm. The tracking system error component was found to be 0.49 mm.
  
  
  CONCLUSIONS
  The Xsight spine tracking system is practically important because it is accurate and eliminates the use of implanted fiducials. Experience has shown this technology to be robust under a wide range of clinical circumstances.
authors.affiliation: Department of Radiation Oncology, Stanford University Medical Center, Stanford, California 94305-5304, USA. tonyho22003@yahoo.com
authors.forename: Anthony K
authors.initials: AK
authors.lastname: Ho
authors.forename: Dongshan
authors.initials: D
authors.lastname: Fu
authors.forename: Cristian
authors.initials: C
authors.lastname: Cotrutz
authors.forename: Steven L
authors.initials: SL
authors.lastname: Hancock
authors.forename: Steven D
authors.initials: SD
authors.lastname: Chang
authors.forename: Iris C
authors.initials: IC
authors.lastname: Gibbs
authors.forename: Calvin R
authors.initials: CR
authors.lastname: Maurer
authors.forename: John R
authors.initials: JR
authors.lastname: Adler
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods*; D013131:Spine / Q000000981:diagnostic imaging / Q000601:surgery*; D015898:Tomography Scanners, X-Ray Computed