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Rapid High Resolution Quality Assurance Phantom and Protocol for 6D Robotic Couches

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A Wiles

A WILES1,2*, T KNEWTSON1,2 , E W IZAGUIRRE1,2,3 , (1) Methodist LeBonheur University Hospital - West Cancer Center, Memphis, TN, (2) University of Missouri, Columbia, MO, (3) University of Tennessee Health Science Center, Memphis, Tennessee


TH-EF-605-9 (Thursday, August 3, 2017) 1:00 PM - 3:00 PM Room: 605

Purpose: To verify the HexaPOD 6D robotic couch for patient positioning and tracking accuracy with submillimeter and fractional angle sensitivity.

Methods: We developed a fast and accurate QA device and protocol using a custom rotated and shifted phantom supporting structure (PSS) where an imaging QA phantom can be placed for fast Eulerian rotation and Cartesian translation verification of robotic couch positioning. Our PSS allows accurate registration of imaging quality assurance phantoms into a robotic couch coordinate system to facilitate cone-beam CT (CBCT) measurements of 6D shifts with respect to an isocentric reference image. We validated our phantom and protocol for precise, reproducible Eulerian rotations and Cartesian translations by evaluating rotational and translational errors in all six dimensions using a procedure integrated with the Elekta XVI 6D-registration algorithm. Alignment marks at phantom isocenter and at off-center calibrated points facilitate phantom positioning, repeatability, and QA standardization between robotic couches. A digital level provides physical verification of robotic couch rotations. A second CBCT image was acquired to determine positioning and repositioning accuracy residual errors.

Results: Hexapod translations and rotations had residual positional errors smaller than 0.1 degrees for any Eulerian rotations and 0.1 mm for any Cartesian translations. Physical rotational measurements concur within 0.1 degrees with Hexapod rotational positioning. Our phantom and protocol supersedes manual alignment tests in resolution and repeatability. CBCT residual imaging corrections are null in the 6D space, which shows that our protocol has higher error detection sensitivity than the XVI CBCT 1/4 mm isocenter voxel resolution.

Conclusion: A novel 3 Dimensional QA phantom was validated as a QA tool to reproducibly and accurately perform 6D HexaPOD robotic couch QA to ensure submillimeter and 1/10th degree image guided radiation therapy (IGRT). The rapid setup and analysis allowed this QA test to be easily integrated into our IGRT QA workflow.

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