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QA of Manipulator-Pointing Accuracy for CyberKnife Using a Cylindrical Diode Array

B Yang*, W Wong , W Lam , H GENG , C Kong , T Lee , K Cheung , S Yu , Hong Kong Sanatorium&Hospital, Hong Kong, Hong Kong


(Sunday, 7/29/2018) 1:00 PM - 1:55 PM

Room: Davidson Ballroom A

Purpose: In CyberKinfe beam delivery, the positioning accuracy of the robotic manipulator is crucial to the final targeting accuracy. The aim of this study was to present a new and quantitative QA method for testing the consistency of manipulator-pointing accuracy of CyberKinfe using the ArcCHECK cylindrical diode array.

Methods: For enabling the fiducial tracking modality during beam deliveries, a cylindrical Styrofoam was tailor-made as an insert of ArcCHECK. Four fiducial markers were implanted in proper positions of the Styrofoam and successfully located in the scanned CT images. An isocentric plan with a total of 116 beams and a fixed 5mm cone was created. Correlation curves, which converted the measured dose difference by the ArcCHECK diode to the robot shift, were obtained by analyzing the dose distributions calculated by MultiPlan after inducing position shifts of ArcCHECK template in AP, LR and SI directions, respectively. After baseline data was taken, more measurements were conducted thereafter and compared with the baseline to calculate the offset of beam paths from the original state. The ability of detecting systematic position error was also evaluated by changing the position of alignment center intentionally.

Results: The reproducibility test based on 1-SD showed a RMS of 0.042 mm with a maximum of 0.295 mm. The mean of position errors in the constancy test was measured to be 0.071 mm with a SD of 0.021 mm and the maximum position error was less than 0.8 mm for all measurements. All induced position errors range from 0.3 mm to 2 mm were detected successfully.

Conclusion: A convenient and efficient method for evaluating the manipulator-pointing accuracy of CyberKnife using ArcCHECK has been developed and proven to be sensitive enough for detecting a systematic drift of robotic manipulator. Our method is capable of assessing the position accuracy of individual beam.


Quality Assurance


TH- External beam- photons: cyberknife

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