Abstract: Objective To investigate the application of ExacTrac X-ray image guidance system in position correction in craniospinal intensity modulated radiation therapy(IMRT). MethodsFrom December 2017 to March 2021, 34 patients underwent craniospinal irradiation were enrolled in this study. Each patient was treated with three target regions, including whole brain section (UP), cervical thoracic section (MID) and lumbosacral section (DOWN). The position of each section of target area was corrected by ExacTrac X'ray image guidance system before treatment, the three translation directions of left and right (Lat), head foot (Long) and ventral dorsal (Vert) axis of each target area and the three rotation directions of Pitch (rotation around Lat), Roll (rotation around Long) and Yaw (rotation around Vert) were obtained, and the positioning error before and after correction was obtained. The nonparametric Wilcoxon signed rank test was used to compare the positioning error before and after correction. ResultsTwenty treatment data were obtained from each patient, and the ExacTrac X'ray system was applied for each treatment. Among the 34 patients, each patient got 680 groups of data before and after correction. The positioning errors of UP target after correction were less than those before correction. Except for the differences in Lat, Long and Pitch directions, the differences in other directions were statistically significant (P<0.05). The positioning errors of MID target after correction were less than those before correction. Except for the differences in Lat and Yaw directions, the differences in other directions were statistically significant (P<0.05). In the DOWN target area, the positioning error after correction was less than that before correction. Except for the difference in Yaw direction, the difference in other directions was statistically significant (P<0.05). The error values before the correction of the translation direction of the target area in UP section were all distributed in (-8-8) mm, and the translation direction after the correction was all distributed in (-1-1) mm; Before the correction of rotation direction, the error value was evenly distributed in (-4-4)°, and after rotation, it was evenly distributed in (-1-1)°. The translation directions of MID section and DOWN section were distributed in (-1010) mm before correction and (-1-1) mm after correction; Before the correction of rotation direction, the error value was evenly distributed in (-4-4)°, and after rotation, it was evenly distributed in (-1-1)°. Conclusion ExacTrac X'ray image guidance system can reduce the positioning error in craniospinal IMRT, which is worthy of clinical application.

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