Program Information
Linear Accelerator Mechanical Quality Assurance Using a Calibrated Camera
D Robertson1*, (1) The University of Texas MD Anderson Cancer Center, Houston, TX
Presentations
SA-B-BRD-9 (Saturday, March 5, 2016) 10:30 AM - 12:30 PM Room: Grand Ballroom D
Purpose: Monthly and annual mechanical quality assurance for linear accelerators (linacs) tests the spatial positioning of components that are essential for accurate delivery of radiation therapy. However, the tools used to perform these measurements are either low-precision (e.g. graph paper or spirit level) or complex and labor-intensive (e.g. Radac device). The purpose of this study is to evaluate the use of a simple calibrated camera system for precise, quantitative measurement of linear accelerator mechanical systems.
Methods: A 1200x1600 pixel CCD camera was calibrated using multiple images of a planar checkerboard pattern and processed with an open-source camera calibration toolbox. The camera was placed on the treatment couch of a Varian TrueBeam linac so that the camera field of view encompassed the light field projected on a white surface placed at 100 cm source-surface distance. The spatial accuracy of the images was verified using images of a ruler. Images of the linac light field were used to measure mechanical parameters including: collimator rotation, optical distance indicator (ODI) accuracy, symmetric and asymmetric jaw positioning, multi-leaf collimator (MLC) positioning, couch motion, and localizing laser position.
Results: The effective resolution of the calibrated camera was 0.3 mm at the center of the images of the linac light field. Interpolation of the light field penumbra, crosshair, laser, and ODI profiles enabled measurements of the jaw, MLC, laser, ODI, and couch lateral and longitudinal position with 0.1 mm-precision. The angular position of the collimator was measured within 0.1 degree. The measurements agreed with historical records of mechanical quality assurance tests for the evaluated linac.
Conclusion: A simple calibrated camera system can be used to precisely measure many of the mechanical properties of medical linacs. This approach provides precise, quantitative measurements that can be used to track the mechanical performance of linac components over time.
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