SU-E-T-53: A New Method for Characterizing the Stability of the Treatment Couch Isocentre

Journal Article · Mon Jun 15 04:00:00 EDT 2015 · Medical Physics

DOI:https://doi.org/10.1118/1.4924414· OSTI ID:22545183

Gete, E; Lee, R ^[1]; Wilson, B ^[2]

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1. BC Cancer Agency, Vancouver Centre, Vancouver, BC (Canada)
2. University of British Columbia, Vancouver, BC (Canada)

Purpose: In this work we propose a new method for characterizing the accuracy of a linear accelerator treatment couch’s isocentre. This is accomplished by a direct determination of the coordinates of the center of rotation as a function of rotation angle. Methods: A phantom consisting of five metallic BBs arranged in a plane was constructed. The phantom was positioned on the treatment couch such that the plane of the BBs was horizontal, while the central BB was aligned with the linac isocentre. With the gantry in the vertical position, the couch was rotated through its full range of rotation while EPID images were acquired every 10 degrees. For each rotation angle, the coordinates of the rotation center were calculated from the displacement of each of the four off-center BBs identified on a pair of EPID images taken between successive rotations. The accuracy of the couch isocentre was evaluated from the distribution of the rotation center coordinates. Our results were compared with film based star-shot measurements of the couch isocentre. Results: The measured couch center of rotation consisted of a cloud of points clustered around the linac isocentre within < 0.7 mm distance. The deviations of these points from the linac isocentre were in the range of 0.01 to 0.20 mm in the cross-plane direction, and 0.10 to 0.61 mm in the in-plane direction, with mean values of 0.09 mm and 0.32 mm. These results were consistent with the results obtained from the star-shot method. Conclusion: A new method for determining the location and accuracy of the couch center of rotation has been successfully implemented. This method gives explicit values of the location and the stability of the couch isocentre, and it can be extended to gantry and collimator rotations.

• OSTI ID: 22545183
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 6 Vol. 42; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

60 APPLIED LIFE SCIENCES
62 RADIOLOGY AND NUCLEAR MEDICINE
ACCURACY
COLLIMATORS
FILM DOSIMETRY
IMAGES
LINEAR ACCELERATORS
PHANTOMS
PHOTOGRAPHIC FILM DOSEMETERS
RADIOTHERAPY