Object The authors describe the technical application of the Xsight Spine Tracking System, data pertaining to accuracy obtained during phantom testing, and the initial clinical feasibility of using this fiducial-free alignment system with the CyberKnife in spinal radiosurgery. Methods The Xsight integrates with the CyberKnife radiosurgery system to eliminate the need for implantation of radiographic markers or fiducials prior to spinal radiosurgery. It locates and tracks spinal lesions relative to spinal osseous landmarks. The authors performed 10 end-to-end tests of accuracy using an anthropomorphic head and cervical spine phantom. Xsight was also used in the treatment of 50 spinal lesions in 42 patients. Dose planning was based on 1.5-mm-thick computed tomography slices in which an inverse treatment planning technique was used. All lesions could be treated using the fiducial-free tracking procedure. Phantom tests produced an overall mean targeting error of 0.52 ± 0.22 mm. The setup time for patient alignment averaged 6 minutes (range 2–45 minutes). The treatment doses varied from 12 to 25 Gy to the median prescription isodose of 65% (40 to 70%). The tumor volume ranged between 1.3 and 152.8 cm3The mean spinal cord volume receiving greater than 8 Gy was 0.69 ± 0.35 cm3No short-term adverse events were noted during the 1- to 7-month follow-up period. Axial and radicular pain was relieved in 14 of 15 patients treated for pain. Conclusions Fiducial-free tracking is a feasible, accurate, and reliable tool for radiosurgery of the entire spine. By eliminating the need for fiducial implantation, the Xsight system offers patients noninvasive radiosurgical intervention for intra- and paraspinal tumors.

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To describe the technological background, the accuracy, and clinical feasibility for single session lung radiosurgery using a real-time robotic system with respiratory tracking. The latest version of image-guided real-time respiratory tracking software (Synchrony®, Accuray Incorporated, Sunnyvale, CA) was applied and is described. Accuracy measurements were performed using a newly designed moving phantom model. We treated 15 patients with 19 lung tumors with robotic radiosurgery (CyberKnife®, Accuray) using the same treatment parameters for all patients. Ten patients had primary tumors and five had metastatic tumors.All patients underwent computed tomography-guided percutaneous placement of one fiducial directly into the tumor, and were all treated with single session radiosurgery to a dose of 24 Gy. Follow up CT scanning was performed every two months.All patients could be treated with the automated robotic technique. The respiratory tracking error was less than 1 mm and the overall shape of the dose profile was not affected by target motion and/or phase shift between fiducial and optical marker motion. Two patients required a chest tube insertion after fiducial implantation because of pneumothorax. One patient experienced nausea after treatment. No other short-term adverse reactions were found. One patient showed imaging signs of pneumonitis without a clinical correlation.Single-session radiosurgery for lung tumor tracking using the described technology is a stable, safe, and feasible concept for respiratory tracking of tumors during robotic lung radiosurgery in selected patients. Longer follow-up is needed for definitive clinical results.

Spinal radiosurgery with the CyberKnife technology is a nonivasive, safe, and effective treatment method for patients with 1 or 2 small spinal malignant tumors. The best benefit of the treatment can be expected in patients with good to excellent clinical condition and patients with severe tumor associated pain.

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