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-rayimage 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-rayimages 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° 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.
The authors would like to thank all radiotherapy technicians at Institute of Biomedical Research and Innovation (IBRI) for data acquisition. We would like to express our appreciation to the entire engineers at Mitsubishi Heavy Industries (MHI) providing detailed mechanical specification
This research was supported by the Japan Society for the Promotion of Science (JSPS) through its “Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program).”
II. METHODS AND MATERIALS
II.A. System description
II.B. Verification of the isocenter alignment of the MHI-TM2000 system
II.B.1. Data acquisition
II.B.2. Coincidence of the laser isocenter and MV beam isocenter
II.B.3. Coincidence of the kV X-ray isocenter and MV beam isocenter
II.B.4. Coincidence of the kV CBCT isocenter and MV beam isocenter
II.C. Verification of the alignment accuracy at off-isocenter positions of the kV X-ray imaging system
II.D. Verification of the localization accuracy by image fusion
III.A. Coincidence of the laser isocenter and MV beam isocenter
III.B. Coincidence of the kV X-ray isocenter and MV beam isocenter
III.C. Coincidence of the kV CBCT isocenter and MV beam isocenter
III.D. Alignment accuracy at off-isocenter positions of the kV X-ray imaging system
III.E. Localization accuracy by image fusion
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