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Evaluation of a Camera-Based External Patient Position Tracking System

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A Jeung

A Jeung*, A Sloutsky , H Mostafavi , Varian Medical Systems Inc., Palo Alto, CA


SU-E-J-195 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

To evaluate the accuracy of a camera-based patient external position monitoring system optimized for localized patient movements.

A prototype software application implements a template-based tracking algorithm. The application generates templates located at strategic points on the patient’s anatomy as seen in an acquired initial video image frame. For subsequent frames, the template pattern is matched in a user-defined region around those points using cross-correlation, and the match is used to determine the local motion at those points.

A motion stage was used to move a fabric sample (representing patient’s clothing) to various positions around a 20 by 20 mm space. An optical camera, at 1.5 m distance, monitored the movement of the sample. At each sample position, the software application evaluated the displacement from initial position based on the camera image; results were compared to the known motion stage displacements.

A motorized breathing manikin was set up on a treatment machine couch. The same optical camera was positioned so as to monitor both breathing and random motion of the manikin in simulation of a clinical treatment scenario. Setups for both torso tracking (respiratory) and face tracking (stereotactic head) conditions were simulated and measured for precision and accuracy.

On the motion stage, calibrated tracking accuracy and precision were both consistently better than 0.5 mm in both vertical and lateral axes. Similar results were achieved for the manikin motion in the clinical simulations.

Localized camera-based tracking is capable of monitoring external changes in patient position to sub-millimeter level. While not able to track internal tumor motion directly, such a system would nonetheless be able to detect tiny movements of the body, bumps, and respiratory motion, any of which may signal a need to check the position of the tumor.

Funding Support, Disclosures, and Conflict of Interest: All work funded by Varian Medical Systems Inc.

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