title: Development of a four-dimensional image-guided radiotherapy system with a gimbaled X-ray head.
abstract: OBJECTIVE
  To develop and evaluate a new four-dimensional image-guided radiotherapy system, which enables precise setup, real-time tumor tracking, and pursuit irradiation.
  
  
  METHODS
  The system has an innovative gimbaled X-ray head that enables small-angle (+/-2.4 degrees ) rotations (pan and tilt) along the two orthogonal gimbals. This design provides for both accurate beam positioning at the isocenter by actively compensating for mechanical distortion and quick pursuit of the target. The X-ray head is composed of an ultralight C-band linear accelerator and a multileaf collimator. The gimbaled X-ray head is mounted on a rigid O-ring structure with an on-board imaging subsystem composed of two sets of kilovoltage X-ray tubes and flat panel detectors, which provides a pair of radiographs, cone beam computed tomography images useful for image guided setup, and real-time fluoroscopic monitoring for pursuit irradiation.
  
  
  RESULTS
  The root mean square accuracy of the static beam positioning was 0.1 mm for 360 degrees of O-ring rotation. The dynamic beam response and positioning accuracy was +/-0.6 mm for a 0.75 Hz, 40-mm stroke and +/-0.4 mm for a 2.0 Hz, 8-mm stroke. The quality of the images was encouraging for using the tomography-based setup. Fluoroscopic images were sufficient for monitoring and tracking lung tumors.
  
  
  CONCLUSIONS
  Key functions and capabilities of our new system are very promising for precise image-guided setup and for tracking and pursuit irradiation of a moving target.
authors.affiliation: Mitsubishi Heavy Industries, Ltd., Tokyo, Japan.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Kamino
authors.forename: Kenji
authors.initials: K
authors.lastname: Takayama
authors.forename: Masaki
authors.initials: M
authors.lastname: Kokubo
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Narita
authors.forename: Etsuro
authors.initials: E
authors.lastname: Hirai
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kawawda
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizowaki
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Nagata
authors.forename: Takehiro
authors.initials: T
authors.lastname: Nishidai
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D004867:Equipment Design; D009068:Movement; D010315:Particle Accelerators / Q000295:instrumentation; D011859:Radiography / Q000295:instrumentation; D011878:Radiotherapy / Q000295:instrumentation*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation; D013679:Technology, Radiologic / Q000295:instrumentation*; D014057:Tomography, X-Ray Computed