Abstract
The image‐guided CyberKnife radiosurgery system is capable of tracking spinal targets without fiducial implants. Recently, a new version of this fiducial‐free image guidance modality (“enhanced Xsight spine tracking”) has been introduced. We assessed the accuracy of this novel technique versus its precursor in a comparative phantom study. The CyberKnife consists of a 6 MV linac on a six‐axis robot and a stereoscopic kV image guidance system. An anthropomorphic head‐and‐neck phantom with a cervical spine section was mounted on the linac nozzle. The robotic manipulator was used to precisely move the phantom to defined positions in the CyberKnife workspace. Multiple stereoscopic images were acquired at different translational and rotational positions. The enhanced Xsight spine tracking readouts were recorded and compared to the nominal phantom position. These tests were repeated with the original Xsight spine tracking version to analyze potential differences. Enhanced Xsight spine tracking correctly reported translational offsets with an RMS error of less than 0.4 mm. Yaw and roll rotations were detected with an accuracy of 0.2°, 0.25°. Pitch offsets were slightly underestimated, with up to 0.3° for an offset of ± 2°. Nominal X (left‐right) translational offsets were partially misinterpreted as roll (0.2° at a 10 mm offset). Apart from this, no correlation between rotational and translational directions was found. In comparison, the original Xsight spine tracking showed identical results for translations, but larger systematic and statistical errors for rotations. Enhanced Xsight spine tracking measurably improves precision in fiducial‐free spinal radiosurgery with the CyberKnife.PACS number: 87.53.Ly
Highlights
Spinal radiosurgery requires precise delivery of large radiation doses to lesions close to the spinal cord
Current delivery systems use image guidance techniques such as kV or MV on-board imaging (OBI), cone beam computed tomography (CT) or stereoscopic imaging to locate the target for patient setup and during treatment.[1]. Spinal image guidance relies either on radioopaque marker implants[2,3] or the bony structure of the spine as a noninvasive alternative.[4,5,6] Digitally reconstructed radiographs (DRRs) calculated from the planning CT or a volumetric dataset are used as the reference for patient position and orientation
The CyberKnife (CK) is a frameless radiosurgery system with a compact 6 MV linac mounted on a robotic arm, which is guided by a stereoscopic imaging system
Summary
Spinal radiosurgery requires precise delivery of large radiation doses to lesions close to the spinal cord. Current delivery systems use image guidance techniques such as kV or MV on-board imaging (OBI), cone beam computed tomography (CT) or stereoscopic imaging to locate the target for patient setup and during treatment.[1] Spinal image guidance relies either on radioopaque marker implants[2,3] or the bony structure of the spine as a noninvasive alternative.[4,5,6] Digitally reconstructed radiographs (DRRs) calculated from the planning CT or a volumetric dataset are used as the reference for patient position and orientation. Since 2005, the CyberKnife is capable of targeting spine lesions by tracking the skeletal structure of adjacent vertebrae. The accuracy of this tracking method has been extensively investigated.[7,8]
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