Room: Exhibit Hall
Purpose: To present long term, 3D polymer gel and patient total system error (TSE) results of a CyberKnifeâ„¢ system.
Methods: The standard radiochromic film (RCF) End-to-End (E2E) test using an anthropomorphic head and neck phantom and isocentric treatment delivery was used with the 6Dskull, Fiducial and Xsightâ„¢ spine (XST) tracking techniques. More than 200 RCF-based E2E results covering the period of more than 10 years were analyzed with respect to tracking method, system hardware and software version, secondary collimation system, and year since installation. An independent polymer gel E2E method was applied, involving a 3D printed head phantom and seven spherical target volumes widely distributed within the brain. Besides phantom measurements TSE was assessed by comparing the delineated target in the planning CT images of a patient treated for a functional target with the radiation induced lesion defined on follow up MR images.
Results: Analysis of the RCF-based TSE results showed mean Â± s.d. values of 0.40 Â± 0.18mm, 0.40 Â± 0.19mm, and 0.55 Â± 0.20mm for the 6Dskull, Fiducial and XST tracking techniques, respectively. Polymer gel TSE values smaller than 0.66 mm were found, showing that the targeting accuracy of the system is sustained even for lesions situated up to 80 mm away from the center of the skull. An average clinical TSE value of 0.87 Â± 0.25mm was also measured using the FSE T2 and FLAIR post treatment MR image data. No changes of TSE over time were shown by the analysis of the long term RCF-based E2E tests.
Conclusion: This study is the first to report long term (> 10 year) analysis of TSE, TSE measurement for targets positioned at large distances from the machine isocenter, and a clinical assessment of TSE for the CyberKnife system. All of these measurements demonstrate TSE <1mm.