Program Information
Fiducial-Based Respiratory Tracking Verification Using A High-Resolution Portable Flat-Panel Detector
J Gersh1,2,3*, R Fulkerson4 , (1) Gibbs Cancer Center & Research Institute - Pelham, Greer , SC, (2) Spectrum Medical Physics LLC, Greenville, SC, (3) Millennium St. Francis Cancer Center, Greenville, SC, (4) RKF Consultants LLC, Dundee, NY
Presentations
SU-E-601-6 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 601
Purpose: The CyberKnife tracks lung lesions using the Synchrony system, where the motion of high-density fiducial markers serves as a surrogate for tumor motion. The authors present a filmless technique aimed at increasing precision and efficiency in the performance of Synchrony QA. Using the QA StereoChecker (QASC, Standard Imaging, Inc., Middleton, WI), a high-resolution portable flat-panel detector, the targeting accuracy of an M6 CyberKnife was determined during the delivery of a Synchrony plan. This study also investigated the variability in targeting accuracy as a function of the speed of a target.
Methods: A 3mm tungsten BB was affixed to a respiratory phantom (CIRS, Norfolk, VA) providing +/- 5mm motion in the superior/inferior direction in a plane parallel to the QASC. The speed of the BB varied between 0.0mm/s and 20mm/s. A single 10mm diameter beam was centered on the BB and perpendicular to the QASC, during which cine images were acquired. Delivery accuracy of the system was quantified by evaluating the variability of the difference between the centers of the radiation field and BB (which appeared as a shadow in the field).
Results: Across all measured speeds, targeting variation followed a normal distribution about the mean. At zero velocity, 95.45% of values fell within 0.10mm of the mean targeting variation value. Targeting variation increased with increasing speed, with measured values of 0.27mm, 0.31mm, 0.43mm, 0.58mm, 0.67mm, 0.65mm, and 0.65mm for 2.5mm/s, 5.0mm/s, 10.0mm/s, 12.5mm/s, 15.0mm/s, 17.5mm/s, and 20.0mm/s, respectively.
Conclusion: Used in conjunction with a motion phantom, the QA StereoChecker can adequately and precisely evaluate the performance of the Synchrony System. At speeds up to 20mm/s, Synchrony was shown to maintain variability of target accuracy with 95.45% of the measured values falling within 0.65mm from the mean. Clinically, this provides useful guidance in defining margins around lung lesions.
Funding Support, Disclosures, and Conflict of Interest: The primary author is the owner of Spectrum Medical Physics LLC of Greenville, SC. This company provides paid consulting services for Standard Imaging Inc. of Middleton, WI. The coauthor is the owner of RKF Consults LLC of Dundee, NY. This company provides paid consulting services for Standard Imaging Inc.
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