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A Real-Time Patient Head Motion Correction Mechanism for MRI-Linac Systems

O Ogunmolu1*, R Wiersma2, (1) University of Pennsylvania, Philadelphia, PA, (2) University of Pennsylvania, Philadelphia, PA


(Tuesday, 7/14/2020) 3:30 PM - 5:30 PM [Eastern Time (GMT-4)]

Room: Track 2

Purpose: demonstrate real-time automatic patient head motion correction during radiation therapy with non-magnetic and non-radiation attenuating robots. Contrary to current methods, this would (i) remove the need for frames or thermoplastic masks; (ii) correct the complex intra/inter-fractional geometric uncertainties; (iii) and be compatible with standalone or combined MRI-Linac systems.

Methods: Inspired from the behavior of the papillae skin of certain cephalopods, we fabricate and test soft actuators which are planar in their reference configuration and deform into 3D shapes in their current configuration in less than 3 seconds. The non-attenuating and non-magnetic actuators were used to construct a robot mechanism whose goal is to move a patient’s head to desired 6-DOF trajectory on a couch. By applying compressed air at defined pressure levels, the mechanism exerts torque on the head along specified axes of motion, yielding desired head motions. We test the setup in open-loop control simulations. Modeled as inflatable domes with continuum and incompressibility constraints, the actuators deform in a Circumferentially COncentric And Radially Symmetric Elastomeric (CCOARSE) manner. Under pressurization, the mechanism’s active actuators moved the head into desired range of motions demonstrating their fast, precise and prehensile head manipulation.

Results: We choose selection maps that activate respective actuators within the mechanism for different axes of motion. Our results show steady-state convergence for head displacement and rotation to target pose as the mechanism moves the head along the respective target axes in <10 seconds.

Conclusion: This work shows the potential of real-time head motion correction with non-magnetic and a radiation-transparent soft robot. This mechanism can be used in emerging hybrid MRI-Linear accelerators. Their continuum nature assures minimal invasiveness and patient comfort. Their actuation medium (air) eliminates the risk of electronic/metallic parts that are unsuitable for the MRI’s magnetic fields and assures safe human-robot interaction.

Funding Support, Disclosures, and Conflict of Interest: The research reported in this publication was supported by National Cancer Institute of the National Institutes of Health under award number R01CA227124.


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