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Motion Tracking Quality Assurance Platform for Leksell Gamma Knife HDMM System

T Chiu*, D Parsons , F Kalantari , S Stojadinovic , UT Southwestern Medical Center, Dallas, TX


(Thursday, 7/18/2019) 10:00 AM - 12:00 PM

Room: 301

Purpose: To develop an in-house motion tracking verification platform for end-to-end testing and routine machine QA of the High Definition Motion Management (HDMM) system for Leksell Gamma Knife Icon.

Methods: The HDMM system consists of an infrared stereoscopic camera, a set of four reference markers, and a tracking (patient) marker. A three-axis translation platform was developed to verify the accuracy of motion tracking system. The platform was designed in AutoDesk 123D Design and fabricated by using MakerBot Z18 3D printer. The platform design incorporated commercial micrometers along each cardinal axis with stated accuracy of 0.01 mm. The range of motion was 20 mm in lateral (x-axis), anterior-posterior (y-axis) and superior-inferior (z-axis) directions. The platform attaches directly onto mask adapter ensuring the same Cartesian coordinate system orientation as Gamma Knife Icon. The camera readings were recorded for individual 1 mm, 2 mm and 3 mm shifts along each axis and for resultant diagonal translation of simultaneous axes shifts with 0.5 mm increment from 0.5 mm to 1.5 mm.

Results: The camera displayed a fluctuating background signal of (0.05±0.01) mm after the HDMM system was initialized and the platform at rest. On average, the difference between set and measured shifts along x-, y- and z-axis were (-0.02±0.06) mm, (-0.03±0.06) mm, and (0.10±0.07) mm, respectively. In diagonal direction, for (0.5,0.5,0.5) mm, (1.0,1.0,1.0) mm and (1.5,1.5,1.5) mm coordinates the difference between expected and measured positions were (-0.07±0.06) mm, (-0.13±0.06) mm and (-0.19±0.06) mm, respectively. With different starting reference locations, similar accuracy results were observed.

Conclusion: A motion tracking platform was developed and used to verify HDMM Gamma Knife tracking accuracy. The analysis showed that HDMM infrared stereoscopic cameras can track motion with sub-millimeter accuracy. The platform can serve as routine machine QA tool to ensure consistency, accuracy and functionality of the HDMM system.


Not Applicable / None Entered.


TH- RT Interfraction motion management : external markers-based

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