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Session: Quality and Safety in Radiotherapy I [Return to Session]

Effect of Skin Color and Camera Obstruction On Accuracy of An Optical Surface Guidance System

R Popple1*, E Covington1,2, D Stanley1, J Fiveash1, (1) The University of Alabama at Birmingham, Birmingham, AL, (2) University of Michigan, Ann Arbor, MI


SU-E-BRA-3 (Sunday, 7/10/2022) 1:00 PM - 2:00 PM [Eastern Time (GMT-4)]

Ballroom A

Purpose: Optical surface guidance is a useful tool for monitoring patient position during frameless radiosurgery. We report on the performance of a commercial surface imaging (SI) system for light and dark skin patients when the SI system has clear and obstructed views.

Methods: Patients were immobilized with an open face thermoplastic mask. The SI region of interest was contoured in the treatment planning system and exported to the SI system. After radiographic image guided positioning, the SI reference was captured. During treatment, the SI system offsets were logged. Following treatment, the linear accelerator trajectory logs were synchronized with SI logs to correlate SI reported offsets with couch and gantry positions. SI offsets were obtained at each table angle for two gantry angles: one at which the SI system had an unobstructed view, and one at which the gantry obstructed the view of one of the SI cameras. Patient race was obtained from the radiation oncology information system as a surrogate for skin color.

Results: 733 fractions were monitored for 263 patients. 521 (71.1%) were white and 143 (19.5%) black. When the SI system had an unobstructed view, the median magnitudes for (white, black) patients were (0.14, 0.18), (0.55, 0.56), (0.45, 0.63), and (0.36, 0.49) mm at table angles 0, 45, 90, and 315 degrees, respectively. When one of the SI cameras was obstructed by the gantry, the median magnitudes were (0.21, 0.29), (0.57, 0.92), (0.46, 0.47), and (0.44, 0.85) mm at table angles 0, 45, 90, and 315 degrees, respectively.

Conclusion: Camera obstruction and skin color both have an effect on the accuracy of the SI system. For white patients, the effect of camera obstruction was less than for black patients. We are working with the vendor to improve system performance and ensure equivalent accuracy for dark skinned patients. .

Funding Support, Disclosures, and Conflict of Interest: The University of Alabama at Birmingham has a product evaluation agreement with Varian Medical Systems for the IDENTIFY system.


Not Applicable / None Entered.


TH- External Beam- Photons: Motion management - intrafraction

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