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A New Methodology of Evaluation of Respiratory Motion Tracking Errors of CyberKnife Using a 2D Detector Array

B Yang*, T Chiu , M Law , K Tang , H GENG , W Lam , K Cheung , S Yu , Hong Kong Sanatorium & Hospital, Hong Kong, Hong Kong


(Sunday, 7/29/2018) 4:30 PM - 5:00 PM

Room: Exhibit Hall | Forum 4

Purpose: The ability of real-time target tracking and the utilization of robotics have been evaluated by many studies. However, most studies either measured the overall targeting accuracy based on film or focused on the tracking of the external surrogate. In this work, a new methodology was developed to quantitatively evaluate the ability of the CyberKnife system to track respiratory motion by measuring radiation beams directly.

Methods: An in-house designed moving phantom coupled with a 2D detector array was used to simulate the respiratory motion in SI and AP directions. A Styrofoam block with four fiducial markers implanted was placed on top of the 2D array for enabling the fiducial based Synchrony Respiratory Tracking. An isocentric plan with a total of 31 beams was created with a fixed 60 mm cone and 150 MU. The measured data saved as the movie files could be used to calculate the beam center shift every 100 ms. The targeting error which could be tracked with a probability in excess of 95% (Ep95) was determined to evaluate the tracking accuracy of the system.

Results: The mean of Ep95 of all beams was measured to be 0.87 0.31 mm (range: 0.36 ~ 1.47 mm) for respiratory motions with amplitudes of 15mm and 20mm. The maximum beam center drift was found to be 2.7 mm. A circle with radius of 0.7 mm could encompass more than 95% of beam centers.

Conclusion: The tracking error of the CyberKnife Synchrony system was successfully evaluated using 2D detector array and was less than 1.5 mm for sinusoidal motion with amplitude as large as 20mm.


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TH- External beam- photons: cyberknife

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