title: Positioning accuracy of a new image-guided radiotherapy system.
abstract: OBJECTIVE
  To evaluate the accuracy of the patient-positioning function of a newly developed image-guided radiotherapy system, the MHI-TM2000 (Mitsubishi Heavy Industries, Ltd., Japan).
  
  
  METHODS
  The isocenter positions prescribed by the lasers, MV treatment beam, and image guidance systems (kV X-ray image and kV-CBCT) were calculated using a cube phantom with a 10-mm-diameter steel ball fixed to the center of the phantom. Then, their location discrepancies were estimated. In addition, to verify the scale and orientation of the coordinate axes of the kV X-ray imaging system, positional measurements were repeated with the phantom placed at 50 mm off-isocenter along the vertical, longitudinal, and lateral directions, respectively. Further, image fusions of an anthropomorphic phantom image and the corresponding image translated by a pre-determined amount were performed.
  
  
  RESULTS
  The isocenter alignment among the coordinate systems was coincident within 0.5 mm in translation for the vertical, longitudinal, and lateral axes, respectively. The geometrical errors at 50 mm off-isocenter for kV X-ray images and CBCT were within 0.2 mm and 1.0 mm, respectively. The image fusion errors were within 1.0 mm in translation and 1.0 degrees in rotation, respectively. No significant difference in the image fusion accuracy was observed between the chest and pelvis phantoms.
  
  
  CONCLUSIONS
  The isocenter alignment among the coordinate systems was performed with high accuracy. Furthermore, the automatic image fusion function achieved sufficient patient positioning accuracy and precision for image-guided radiotherapy.
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Kyoto University Graduate School of Medicine, Kyoto 6068507, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Miyabe
authors.forename: Akira
authors.initials: A
authors.lastname: Sawada
authors.forename: Kenji
authors.initials: K
authors.lastname: Takayama
authors.forename: Shuji
authors.initials: S
authors.lastname: Kaneko
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizowaki
authors.forename: Masaki
authors.initials: M
authors.lastname: Kokubo
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis / Q000379:methods; D011881:Radiotherapy, Computer-Assisted / Q000295:instrumentation*; D020266:Radiotherapy, Conformal / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*