Verification of Accuracy of CyberKnife Tumor-tracking Radiation Therapy Using Patient-specific Lung Phantoms

Purpose: To investigate the accuracy of the CyberKnife Xsight Lung Tracking System (XLTS) compared with that of a fiducial-based target tracking system (FTTS) using patient-specific lung phantoms. Methods and Materials: Three-dimensional printing technology was used to make individualized lung phantoms that closely mimicked the lung anatomy of actual patients. Based on planning computed tomographic data from 6 lung cancer patients who underwent stereotactic ablative radiation therapy using the CyberKnife, the volume above a certain Hounsfield unit (HU) was assigned as the structure to be filled uniformly with polylactic acid material by a 3-dimensional printer (3D Edison, Lokit, Korea). We evaluated the discrepancies between the measured and modeled target positions, representing the total tracking error, using 3 log files that were generated during each treatment for both the FTTS and the XLTS. We also analyzed the gamma index between the film dose measured under the FTTS and XLTS. Results: The overall mean values and standard deviations of total tracking errors for the FTTS were 0.36 +/- 0.39 mm, 0.15 +/- 0.64 mm, and 0.15 +/- 0.62 mm for the craniocaudal (CC), left-right (LR), and anteroposterior (AP) components, respectively. Those for the XLTS were 0.38 +/- 0.54 mm, 0.13 +/- 0.18 mm, and 0.14 +/- 0.37 mm for the CC, LR, and AP components, respectively. The average of gamma passing rates was 100% for the criteria of 3%, 3 mm; 99.6% for the criteria of 2%, 2 mm; and 86.8% for the criteria of 1%, 1 mm. Conclusions: The XLTS has segmentation accuracy comparable with that of the FTTS and small total tracking errors. (C) 2015 Elsevier Inc. All rights reserved.