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Evaluation of the Accuracy of a Six Degree of Freedom Robotic Couch Using Optical Surface and Conebeam CT Images of An SRS QA Phantom

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Q Zhang

Q Zhang*, Y Chen , J Zhang , Y Cao , E Klein , Long Island Jewish Medical Center, Lake Success, NY


SU-I-GPD-T-544 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The accuracy of six degree of freedom (6DOF) robotic couch was examined using optical surface and Conebeam CT (CBCT) images of an SRS QA Phantom.

Methods: The CBCT and Optical surface images of the SRS phantom (Varian) were taken at different pitch, roll and rotation angles. Those angles varied from -3 to 3 degrees by input from the service console. We have randomly generated a total of 39 combinations of Pitch, roll and rotations using the 6DOF couch. The Optical surface images were taken and the Vision RT software was used to determine the rotation angles and isocenter shifts. The CBCTs of the SRS QA phantom were taken for each angulation at 3 degree from its zero position. The center positions of the 5 tungsten carbide BBs contained in the SRS QA phantom were determined with in-house software. The expected BBs positions at different rotation angles were determined by applying a combined translation/rotation operator to the BB positions at neutral values. A least square method was used to minimize the difference between the expected BBs positions and their measured positions.

Results: A total of 39 optical images were analyzed. Among the 39 calculations, the maximum rotation angle differences were 0.2, 0.1, and -0.2 degrees, for pitch, roll, and couch rotation, respectively. The maximum isocenter shifts were -0.80 mm, 0.7 mm, and -0.10 mm in lateral, longitudinal and vertical axes, respectively. The 8 CBCT images were also analyzed. The maximum rotation angles were 0.20 degree for pitch, roll and rotations.

Conclusion: The accuracy of the Varian couch was studied with optical surface and CBCT images of the SRS QA phantom. The rotational errors were less than 0.2 degree and isocenter shifts were less than 0.8 mm in each direction. This accuracy for the 6DOF system is sufficient for SRS applications.

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