Setup error and residual error analysis of ExacTrac X-ray image guidance system in stereotactic radiotherapy for brain metastases

Abstract

ObjectiveThis study aims to analyze the setup errors of the ExacTrac X-ray image guidance system in stereoscopic radiotherapy for brain metastases and discuss the necessity of setup error verification after bed angle movement. MethodsTwelve patients with brain metastases were treated with stereotactic radiotherapy. ExacTrac X-ray image guidance system was used to register and verify the image. Besides, the intra- and inter-fractional setup errors and residual errors were analyzed. ResultsTwelve patients received head stereotactic radiotherapy 56 times. The inter-fractional setup errors and residual errors were x (1.04 ± 0.16) and (0.15 ± 0.05) mm in left and right directions, y (1.25 ± 0.28) and (0.18 ± 0.07) mm in head and foot direction, and z (0.93 ± 0.81) and (0.14 ± 0.13) mm in abdominal and dorsal direction, respectively; Rx (0.81 ± 0.24) and (0.24 ± 0.09) degree in the sagittal plane, Ry (0.95 ± 0.19), (0.22 ± 0.06) degree in the cross-section, and Rz (1.03 ± 0.26), (0.22 ± 0.06) in the coronal plane. The difference was statistically significant (P < 0.05). Only 19.6% of the intra-fractional non-coplanar arc setup verification passed without correction for the first time, and the others were significantly improved after correction, presenting statistical significance (P < 0.05). The inter-fractional setup errors and residual errors were x (0.82 ± 0.25) and (0.13 ± 0.04) mm in left and right directions, y (0.67 ± 0.23) and (0.18 ± 0.08) mm in head and foot direction, and z (0.74 ± 0.21) and (0.19 ± 0.08) mm in abdominal and dorsal direction, respectively; Rx (0.67 ± 0.13) and (0.20 ± 0.08) degree in the sagittal plane, Ry (0.68 ± 0.13) and (0.17 ± 0.10) degree in the cross-section, and Rz (0.60 ± 0.28) and (0.19 ± 0.07) degree in the coronal plane. The difference was statistically significant (P < 0.05). ConclusionThe ExacTrac image guidance system enhanced the accuracy of setup in stereoscopic radiotherapy for brain metastases and satisfied the clinical requirements. It is necessary to verify the non-coplanar arc setup.