Advances in fiducial‐free image‐guidance for spinal radiosurgery with CyberKnife – a phantom study

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

Investigating the clinical advantages of a robotic linac equipped with a multileaf collimator in the treatment of brain and prostate cancer patients

“…Image registration is based on the location of gold markers implanted in soft tissue such as prostate, or based on anatomical bony landmarks such as the skull or vertebral bodies, or based on the center of mass of lung lesions directly. (1,2,3) For tumors that move with respiration (e.g., lung, liver, pancreas), the CyberKnife correlates this image registration with continuous reading of external optical markers on the patient's chest to create a prediction model. This prediction model is continuously updated during treatment delivery with additional images so as to gradually adapt to changing respiratory pattern.…”

Fiducial-free CyberKnife radiosurgery for residual metastatic spinal tumor after decompression and instrumentation

“…The DRR are pre-calculated from the planning CT dataset in a ray-casting process with data sampling of 2 mm along the kV X-ray beam. 11,12 In Patient 1, we could not match enough surface points on the vertebral body with the matching grid because the points on the titanium screw caused errors within the Xsight-Spine system. However, there is considerable forward curvature at the T4 level and pedicle inclinations change gradually from T2 to T6 (which is not seen at T12).…”

“…10 The image-guided CyberKnife radiosurgery system is capable of tracking spinal targets without fiducial implants, and a new version of this fiducial-free image guidance modality, ''Enhanced Xsight-Spine Tracking'', has been introduced. 11 This method is accurate, reliable and effective in the treatment of spinal lesions. 11,12 We consider limitations to the technique for the treatment of residual metastatic spinal tumors after decompression and instrumentation.…”

“…11 This method is accurate, reliable and effective in the treatment of spinal lesions. 11,12 We consider limitations to the technique for the treatment of residual metastatic spinal tumors after decompression and instrumentation. High instrumentation density can cause image distortion of the digitally reconstructed radiographs (DRR) calculated from the planning CT scans, thereby impairing DRR matching with live radiographic images.…”

CyberKnife robotic spinal radiosurgery in prone position: dosimetric advantage due to posterior radiation access?

“…With the recent release of CK software version 9.6 in 2012, a new tracking modality called "Xsight Spine Prone" (Accuray Inc.) combines the current spine image registration algorithm (7) with dynamic compensation of respiratory motion. Thus, spinal targets can now also be targeted in prone position.…”