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Program Information

To Check the Accuracy of 6DoF (degrees-Of-Freedom) Couch Using a Novel Method

G Gill

G Gill*, J Chang , Northwell Health, Lake Success, NY


SU-H1-GePD-J(B)-6 (Sunday, July 30, 2017) 3:00 PM - 3:30 PM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: To check the accuracy of 6 DoF (degree-of-freedom) couch using Varian’s developer mode application.

Methods: Evaluation of geometric accuracy of 6DoF couch was performed using an in-house built phantom consisting of set of bb’s and a ruler placed at different plane. Custom XML scripts were written to program the movement of 6DoF couch for various pitch, yaw and roll angles along with the acquisition of KV/MV images for each angle. Preliminary tests were performed first to assure the translational axis accuracy and leveling of the couch with the standard machine calibration equipment. The phantom was then placed on the couch and aligned with lasers. Varian’s developer mode application was activated to move the 6DoF couch to the programmed position; KV/MV beams delivered and images of the phantom were acquired following the commands in the XML file automatically and sequentially. Mathematical algorithm was developed to calculate the actual pitch, yaw and roll angles from the KV/MV images of the phantom and the results were compared with the programmed angles.

Results: The accuracy of pitch, yaw and roll was tested for ±3 degree of rotational angle with a 0.5 degree increment. Linear regression of the measured (y) and planned (x) angles for pitch was y=0.972x-0.0353 with R²=0.9988 and a maximal discrepancy of ±0.16 degrees. For roll, it is y=0.8873x+0.2 with R²=0.9984 and a maximal discrepancy of ±0.56 degrees. For yaw the result is y=0.9904x-0.1323 with R²=0.9977 and a maximal discrepancy of ±0.31 degrees. While performing all the relevant tests, we have noticed that MV detector and KV detector were displaced off mechanically from isocenter axis position.

Conclusion: The developed test can be used to automate the annual quality assurance or commissioning of 6 DoF couch.

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