[BibTex]

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Abstract: Objective: To evaluate clinical targeting precision in fiducial\-free spinal treatments with a robotic radiosurgery system (Cyberknife). Methods: For assessment of spine tracking system performance, we conducted phantom tracking tests on cervical and thoracic vertebrae. We retrospectively evaluated intrafraction patient movement for cervical (47), thoracic (90) and lumbar (90) treatments. A conservative measure for the expected targeting error due to patient motion was derived. Results: The phantom tests show that spinal targets are detected with an accuracy of \<0.2 mm for the translational and \<0.3\° for the rotational directions. The mean targeting error per beam due to residual patient motion is determined to be as low as 0.28+/\-0.13 mm (X), 0.25+/\-0.15 mm (Y), 0.19+/\-0.11 mm (Z) for translational shifts and 0.40+/\-0.20\° (roll), 0.20+/\- 0.08\° (pitch) and 0.19+/\-0.08\° (yaw) for rotations. Interestingly, the tracked spine section is of little significance for the overall targeting error due to motion, which is below 1 mm for more than 95\% of our spinal treatments (median: 0.48 mm). Conclusions: We could demonstrate that image\-guided spinal radiosurgery with the Cyberknife allows for submillimeter precision in treatment delivery despite of patient motion