title: A new irradiation unit constructed of self-moving gantry-CT and linac.
abstract: OBJECTIVE
  To improve reproducibility in stereotactic irradiation (STI) without using noninvasive immobilization devices or body frames, we have developed an integrated computed tomography (CT)-linac irradiation system connecting CT scanner and linac via a common treatment couch.
  
  
  METHODS
  This system consists of a linac, a CT scanner, and a common treatment couch. The linac and the CT gantry are positioned on opposite ends of the couch so that, by rotating the treatment couch, linac radiotherapy or CT scanning can be performed. The rotational axis of the linac gantry is coaxial with that of the CT gantry, and the position of the linac isocenter on the couch matches the origin of the coordinate system for CT scanning when the couch is rotated 180 degrees toward the CT side. Instead of the couch moving into the gantry, as in conventional CT, in this case the table is fixed and scanning is accomplished by moving the gantry. We evaluated the rotational accuracy of the common couch and the scan-position accuracy of the self-moving gantry CT.
  
  
  RESULTS
  The positional accuracy of the common couch was 0.20, 0.18, and 0.39 mm in the lateral, longitudinal, and vertical directions, respectively. The scan-position accuracy of the CT gantry was less than 0.4 mm in the lateral, longitudinal, and vertical directions.
  
  
  CONCLUSIONS
  This irradiation system has a high accuracy and is useful for noninvasive STI and for verification of the position of a target in three-dimensional conformal radiotherapy.
authors.affiliation: Department of Radiation Oncology, University of Yamanashi, School of Medicine, Japan. kuriyama@res.yamanashi-med.ac.jp
authors.forename: Kengo
authors.initials: K
authors.lastname: Kuriyama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Onishi
authors.forename: Naoki
authors.initials: N
authors.lastname: Sano
authors.forename: Takafumi
authors.initials: T
authors.lastname: Komiyama
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Aikawa
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Tateda
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Araki
authors.forename: Minoru
authors.initials: M
authors.lastname: Uematsu
mesh_terms: D004867:Equipment Design; D055585:Physical Phenomena; D010825:Physics; D016634:Radiosurgery / Q000295:instrumentation*; D020266:Radiotherapy, Conformal / Q000295:instrumentation*; D015898:Tomography Scanners, X-Ray Computed