title: The utility of megavoltage computed tomography images from a helical tomotherapy system for setup verification purposes.
abstract: OBJECTIVE
  To evaluate the utility of relatively low-dose megavoltage computed tomography (MVCT) images from a clinical helical tomotherapy system for setup verification purposes.
  
  
  METHODS
  Cross-sectional kilovolt computed tomography (kVCT) images were obtained for treatment planning purposes on a diagnostic third-generation CT scanner, followed by MVCT images from a helical tomotherapy system in 8 pet dogs with spontaneously occurring tumors. The kVCT and MVCT images were aligned for setup verification purposes, allowing repositioning before treatment delivery.
  
  
  RESULTS
  Tumors are readily visualized on the MVCT images. At a dose of 2-3 cGy, the MVCT images are of sufficient quality for verification of treatment setup, but soft-tissue contrast is inferior to that with conventional kVCT. The MV and kVCT images were successfully aligned. When necessary, patients undergoing helical tomotherapy were repositioned before treatment.
  
  
  CONCLUSIONS
  Megavoltage CT image quality is sufficient for tumor identification and three-dimensional setup verification in dogs with spontaneous tumors. The MVCT images can be aligned with the planning kVCT to ensure proper patient registration before treatment. Image alignment was successful in these canine patients, despite no skin markings defining patient positioning between the two scans. MVCT images facilitate setup verification, and their tomographic nature offers improvements over conventional portal imaging.
authors.affiliation: Department of Human Oncology, University of Wisconsin, Madison, WI, USA. forrestl@svm.vetmed.wisc.edu
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Forrest
authors.forename: Thomas Rockwell
authors.initials: TR
authors.lastname: Mackie
authors.forename: Ken
authors.initials: K
authors.lastname: Ruchala
authors.forename: Michelle
authors.initials: M
authors.lastname: Turek
authors.forename: Jeff
authors.initials: J
authors.lastname: Kapatoes
authors.forename: Hazim
authors.initials: H
authors.lastname: Jaradat
authors.forename: Susanta
authors.initials: S
authors.lastname: Hui
authors.forename: John
authors.initials: J
authors.lastname: Balog
authors.forename: David M
authors.initials: DM
authors.lastname: Vail
authors.forename: Minesh P
authors.initials: MP
authors.lastname: Mehta
mesh_terms: D000818:Animals; D001859:Bone Neoplasms / Q000532:radiotherapy* / Q000662:veterinary; D002138:Calibration; D004283:Dog Diseases / Q000532:radiotherapy; D004285:Dogs; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy* / Q000662:veterinary; D012516:Osteosarcoma / Q000532:radiotherapy* / Q000662:veterinary; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000295:instrumentation / Q000379:methods*; D036542:Tomography, Spiral Computed / Q000295:instrumentation / Q000379:methods*