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Program Information

Commissioning a Six Degree of Freedom Couch

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D Roberts

D Roberts*, K Lam , J Bredfeldt , E Covington , University of Michigan Hospital and Health Systems, Ann Arbor, MI


SU-F-J-37 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

The proper operation of a six degree of freedom couch (6DOFC) to position a patient for treatment requires that a number systems on the treatment unit work together correctly. Commissioning a 6DOFC requires not only the commissioning of each separate system but also commissioning the interactions between the systems.

To commission a 6DOFC, we tested the resolvers that readout the linear and angular positions; the orthogonality of the axes of the laser positioning system, the imaging system, the gantry and the couch as well as their relationship to each other. An automated Winston-Lutz test was used verify the coincidence of the origins of the laser system, imaging system and treatment unit. The IsoCal phantom was used to verify the consistency of axes orientations between systems. The operation of the couch and imaging system was verified under simulated load conditions and an end to end test was performed to verify correct operation of the system.

The tests on the couch resolvers, orthogonality and coincidence of the axes of each system were successfully completed and showed excellent agreement. The automated Winston-Lutz test showed that the maximum displacement of the center of the radiation field with respect to the isocenter was <0.6 mm (radius) at isocenter. The analysis of the IsoCal phantom showed that the maximum variation of the radiation field with respect to known locations in the phantom was ~0.9 mm for all the BBs in the phantom. Load tests showed maximum errors of 1 mm.

We tested all system associated with the 6DOFC and found the uncertainty due to imaging was <.9mm and the uncertainty due to loading ~1 mm, resulting in a total error of ~1.4 mm.

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