title: Clinical experiences with onboard imager KV images for linear accelerator-based stereotactic radiosurgery and radiotherapy setup.
abstract: OBJECTIVE
  To report our clinical experiences with on-board imager (OBI) kV image verification for cranial stereotactic radiosurgery (SRS) and radiotherapy (SRT) treatments.
  
  
  METHODS
  Between January 2007 and May 2008, 42 patients (57 lesions) were treated with SRS with head frame immobilization and 13 patients (14 lesions) were treated with SRT with face mask immobilization at our institution. No margin was added to the gross tumor for SRS patients, and a 3-mm three-dimensional margin was added to the gross tumor to create the planning target volume for SRT patients. After localizing the patient with stereotactic target positioner (TaPo), orthogonal kV images using OBI were taken and fused to planning digital reconstructed radiographs. Suggested couch shifts in vertical, longitudinal, and lateral directions were recorded. kV images were also taken immediately after treatment for 21 SRS patients and on a weekly basis for 6 SRT patients to assess any intrafraction changes.
  
  
  RESULTS
  For SRS patients, 57 pretreatment kV images were evaluated and the suggested shifts were all within 1 mm in any direction (i.e., within the accuracy of image fusion). For SRT patients, the suggested shifts were out of the 3-mm tolerance for 31 of 309 setups. Intrafraction motions were detected in 3 SRT patients.
  
  
  CONCLUSIONS
  kV imaging provided a useful tool for SRS or SRT setups. For SRS setup with head frame, it provides radiographic confirmation of localization using the stereotactic target positioner. For SRT with mask, a 3-mm margin is adequate and feasible for routine setup when TaPo is combined with kV imaging.
authors.affiliation: Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY, USA.
authors.forename: Linda X
authors.initials: LX
authors.lastname: Hong
authors.forename: Chin C
authors.initials: CC
authors.lastname: Chen
authors.forename: Madhur
authors.initials: M
authors.lastname: Garg
authors.forename: Ravindra
authors.initials: R
authors.lastname: Yaparpalvi
authors.forename: Dennis
authors.initials: D
authors.lastname: Mah
mesh_terms: D001932:Brain Neoplasms / Q000175:diagnosis / Q000532:radiotherapy* / Q000601:surgery*; D016371:Cranial Irradiation / Q000379:methods; D003952:Diagnostic Imaging / Q000379:methods; D004867:Equipment Design; D006801:Humans; D007103:Immobilization / Q000295:instrumentation / Q000379:methods; D007834:Lasers; D011786:Quality Control; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods / Q000592:standards; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods