Objective  Two tracking modes are provided for treating spinal tumors with Cyberknife: Xsight spine tracking (XST) and Xsight spine prone tracking (XSPT). In this study, the positioning errors of the two spinal tracking modes were compared to evaluate the accuracy of the XSPT mode in treating patients with spinal tumors.

  Methods  Eighteen patients with lumbosacral spinal tumors were retrospectively selected at Peking University Third Hospital from July 2020 to June 2021. CT-simulated localization was performed in the supine (fixed with vacuum pad) and prone (fixed with thermoplastic mask and prone plate) positions. The treatment plans for the supine position were designed using the XST methods, and those for the prone position were designed using the XSPT method. During treatment, the spinal tracking correction errors of the two postures were recorded. The movement-corrected errors included the following three directions: inferior-superior (I-S), left-right (L-R), and anterior-posterior (A-P). The angle-corrected errors included clockwise-anticlockwise, pitch, and tilt. Furthermore, correlation errors of synchrony respiratory tracking in the prone position were recorded. Parameters of corrected error for the two tracking modes were analyzed using the paired t-test statistical method to compare the differences in the positioning accuracy between the two groups. In addition, correlation errors of the synchrony respiratory model in the prone position were analyzed to evaluate the prediction accuracy of the respiratory model.

  Results  The correction error of the supine position in the A-P direction was (0.18±0.16) mm, and that of the prone position was (0.31 ± 0.26) mm (P<0.05). The correction error of the supine position in the I-S direction was (0.27±0.24) mm, and that of the prone position was (0.5±0.4) mm (P <0.05). The average correlation errors of the synchrony model for the L-R, I-S and A-P directions of the prone position were (0.21±0.11) mm, (0.41±0.38) mm, and (0.68±0.42) mm, respectively.

  Conclusions  Because of the effect of respiratory movement during treatment, compared with the positioning error of the supine position, that of the prone position in the A-P and I-S directions is relatively large. However, the prone position mode has a synchronous tracking system that can correct the error of respiratory motility in real time to realize accurate target irradiation. Therefore, the consistency and accuracy of the XSPT mode meets the clinical treatment requirements.