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Session: Novel Imaging and Therapy Solutions [Return to Session]

6-DoF Intrafraction Cranial Motion Detection Using Capacitive Sensing Technology: Simulation and Volunteer Study

P Sadeghi1*, D Bastin-DeCoste2, J Robar2 (1) Princess Margaret Cancer Centre, Toronto, ON, Canada, (2) Nova Scotia Health Authority, Halifax, NS, Canada


MO-F-BRC-1 (Monday, 7/11/2022) 1:45 PM - 2:45 PM [Eastern Time (GMT-4)]

Ballroom C

Purpose: To introduce and evaluate a novel non-contact, non-ionizing and continuous capacitive motion detection system for 6-DoF cranial intrafraction motion detection using a combination of Finite Element Analysis (FEA) simulations and a volunteer study.

Methods: Capacitive sensing leverages the human body’s natural conductivity and measures the capacitance between the human cranium and an array of conductive sensors in close proximity. Cranial motion is measured as a change in capacitance. A cranial FEA model was devised and verified against experimental results. The model was used to simulate and compare potential capacitive array designs. Sensitivity to translational and rotational motion and uniqueness of response to 6-DoF motion were used to determine the most promising design for a prospective volunteer study.The study included twenty-five volunteers, fitted with S-frame thermoplastic masks. Volunteers took part in one data acquisition session per day for three consecutive days. The conductive array was translated and rotated relative to each volunteer’s immobilized cranium in 1-millimetre/1-degree steps to simulate cranial motion. Capacitive signals were collected at 20 Hz. Data from the first acquisition session for each volunteer was used to train logistic regression classifier models and establish calibration equations that were used on data from their subsequent acquisition sessions to evaluate the system performance.

Results: The trained classifiers had an average success rate of 92.6% for 6-DoF motion classification. The average detection precision was 0.04±0.02 mm, 0.08±0.03 mm, and 0.14±0.07 mm for superior-inferior, lateral, and anterior-posterior translations, respectively, and 0.5±0.3°, 0.05±0.03°, and 0.07±0.04° for roll, pitch, and yaw rotations, respectively.

Conclusion: This novel technology permits continuous classification and quantification of 6-DoF motion of the cranium within the immobilizer mask, providing average translational and rotational sensing within 0.14 mm and 0.5°, respectively. The system is portable and modular, allowing use during treatment delivery or imaging procedures.

Funding Support, Disclosures, and Conflict of Interest: The authors acknowledge financial support from the Atlantic Canada Opportunities Agency (ACOA), Atlantic Innovation Fund (AIF), and Brainlab AG.


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