title: CT image-guided intensity-modulated therapy for paraspinal tumors using stereotactic immobilization.
abstract: OBJECTIVE
  To design and implement a noninvasive stereotactic immobilization technique with daily CT image-guided positioning to treat patients with paraspinal lesions accurately and to quantify the systematic and random patient setup errors occurring with this method.
  
  
  METHODS
  A stereotactic body frame (SBF) was developed for "rigid" immobilization of paraspinal patients. The inherent accuracy of this system for stereotactic CT-guided treatment was evaluated with phantom studies. Seven patients with thoracic and lumbar spine lesions were immobilized with the SBF and positioned for 33 treatment fractions using daily CT scans. For all 7 patients, the daily setup errors, as assessed from the daily CT scans, were corrected at each treatment fraction. A retrospective analysis was also performed to assess what the impact on patient treatment would have been without the CT-based corrections (i.e., if patient setup had been performed only with the SBF).
  
  
  RESULTS
  The average magnitude of systematic and random errors from uncorrected patient setups using the SBF was approximately 2 mm and 1.5 mm (1 SD), respectively. For fixed phantom targets, the system accuracy for the SBF localization and treatment was shown to be within 1 mm (1 SD) in any direction. Dose-volume histograms incorporating these uncertainties for an intensity-modulated radiotherapy plan for lumbar spine lesions were generated, and the effects on the dose-volume histograms were studied.
  
  
  CONCLUSIONS
  We demonstrated a very accurate and precise method of patient immobilization and treatment delivery based on a noninvasive SBF and daily image guidance for paraspinal lesions. The SBF provides excellent immobilization for paraspinal targets, with setup accuracy better than 2 mm (1 SD). However, for highly conformal paraspinal treatments, uncorrected systematic and random errors of 2 mm in magnitude can result in a significantly greater (>100%) dose to the spinal cord than planned, even though the planned target coverage may not change substantially. With daily CT guidance using the SBF, we showed that the maximal spinal cord dose is ensured to be within 10-15% of the planned value.
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA. yenicek@mskcc.org
authors.forename: Kamil M
authors.initials: KM
authors.lastname: Yenice
authors.forename: D Michael
authors.initials: DM
authors.lastname: Lovelock
authors.forename: Margie A
authors.initials: MA
authors.lastname: Hunt
authors.forename: Wendell R
authors.initials: WR
authors.lastname: Lutz
authors.forename: Nathalie
authors.initials: N
authors.lastname: Fournier-Bidoz
authors.forename: Chia-Ho
authors.initials: CH
authors.lastname: Hua
authors.forename: Josh
authors.initials: J
authors.lastname: Yamada
authors.forename: Mark
authors.initials: M
authors.lastname: Bilsky
authors.forename: Henry
authors.initials: H
authors.lastname: Lee
authors.forename: Karl
authors.initials: K
authors.lastname: Pfaff
authors.forename: Spiridon V
authors.initials: SV
authors.lastname: Spirou
authors.forename: Howard I
authors.initials: HI
authors.lastname: Amols
mesh_terms: D006801:Humans; D007103:Immobilization; D008159:Lumbar Vertebrae; D009068:Movement; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000592:standards; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013125:Spinal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D013238:Stereotaxic Techniques; D013904:Thoracic Vertebrae; D014057:Tomography, X-Ray Computed