CyberKnife Xsight versus Fiducial-based Target-tracking: A Novel 3D Dosimetric Comparison in a Dynamic Phantom

Abstract

Background: The CyberKnife Xsight lung-tracking system (XLTS) provides an alternative to fiducial-based target-tracking systems (FTTS) for non-small-cell lung cancer (NSCLC) patients without invasive fiducial insertion procedures. This study provides a method for 3D independent dosimetric verification of the accuracy of the FTTS compared to the XLTS without relying on log-files generated by the CyberKnife system. Methods: A respiratory motion trace was taken from a 4D-CT of a real lung cancer patient and applied to a modified QUASARTM respiratory motion phantom. A novel approach to 3D dosimetry was developed using Gafchromic EBT3 film, allowing the 3D dose distribution delivered to the moving phantom to be reconstructed. Treatments were planned using the recommended margins for one and three fiducial markers and XLTS 2-view, 1-view and 0-view target-tracking modalities. The dose delivery accuracy was analysed by comparing the reconstructed dose distributions to the planned dose distributions using gamma index analysis. Results: For the 3%/2mm gamma criterion, gamma passing rates up to 99.37% were observed for the static deliveries. The 3-fiducial and 1-fiducial-based deliveries exhibited passing rates of 93.74% and 97.82%, respectively, in the absence of target rotation. When target rotation was considered, the passing rate for 1-fiducial tracking degraded to 91.24%. The passing rates observed for XLTS 2-view, 1-view and 0-view target-tracking were 92.78%, 96.22% and 76.08%, respectively. Conclusions: Except for the XLTS 0-view, the dosimetric accuracy of the XLTS was comparable to the FTTS under equivalent treatment conditions. This study gives us further confidence in the CyberKnife XLTS and FTTS systems.

A retrospective multi‐center feasibility study of a new PTV margin estimation approach for moving targets using CyberKnife log files

“…In general, error assessment is necessary for the CK to study the impact of delivery uncertainties and select appropriate PTV margins. In this context, a review of previous studies reveals several sources of error 7–17 . Nakayama et al.…”

“…In this context, a review of previous studies reveals several sources of error. [7][8][9][10][11][12][13][14][15][16][17] Nakayama et al and Descovich et al found that the PTV margin estimation requires the consideration of STRS modeling and prediction errors. 7,9 According to Yang et al study, the CK system has five main sources of error.…”

“…In this context, a review of previous studies reveals several sources of error. 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 Nakayama et al. and Descovich et al.…”