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Development and Evaluation of a Real-Time Robotic 6D Quality Assurance Phantom

A Belcher

AH Belcher*, X Liu , Z Grelewicz , RD Wiersma , The University of Chicago, Chicago, IL


SU-F-BRE-5 Sunday 4:00PM - 6:00PM Room: Ballroom E

Purpose: A 6 degree-of-freedom robotic phantom capable of reproducing dynamic tumor motion in 6D was designed to more effectively match solid tumor movements throughout pre-treatment scanning and radiation therapy. With the abundance of optical and x-ray 6D real-time tumor tracking methodologies clinically available, and the substantial dosimetric consequences of failing to consider tumor rotation as well as translation, this work presents the development and evaluation of a 6D instrument with the facility to improve quality assurance.

Methods: An in-house designed and built 6D robotic motion phantom was constructed following the so-called Stewart-Gough parallel kinematics platform archetype. The device was then controlled using an inverse kinematics formulation, and precise movements in all six degrees of freedom (X, Y, Z, pitch, roll, and yaw) as well as previously obtained cranial motion, were effectively executed. The robotic phantom movements were verified using a 15 fps 6D infrared marker tracking system (Polaris, NDI), and quantitatively compared to the input trajectory. Thus, the accuracy and repeatability of 6D motion was investigated and the phantom performance was characterized.

Results: Evaluation of the 6D platform demonstrated translational RMSE values of 0.196 mm, 0.260 mm, and 0.101 mm over 20 mm in X and Y and 10 mm in Z, respectively, and rotational RMSE values of 0.068 degrees, 0.0611 degrees, and 0.095 degrees over 10 degrees of pitch, roll, and yaw, respectively. The robotic stage also effectively performed controlled 6D motions, as well as reproduced cranial trajectories over 15 minutes, with a maximal RMSE of 0.044 mm translationally and 0.036 degrees rotationally.

Conclusion: This 6D robotic phantom has proven to be accurate under clinical standards and capable of reproducing tumor motion in 6D. Consequently, such a robotics device has the potential to serve as a more effective system for IGRT QA that involves both translational and rotational dimensions.

Funding Support, Disclosures, and Conflict of Interest: Research was partially funded by NIH Grant T32 EB002103-21 from NIBIB. Contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIBIB or NIH.

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