The Accuracy of Surface Guided Hypofractionated Radiotherapy for Intracranial Metastasis With Open Face Mask Immobilization.

Purpose/Objective(s) To investigate the applicability of surface imaging for image guidance in the hypofractionated radiotherapy for intracranial metastasis with open face mask immobilization. Materials/Methods Nineteen patients were treated with hypofractionated radiotherapy for intracranial metastasis were included. Before the start of treatment, each patient underwent simulation with open face mask immobilization. During treatment, CBCT images were collected for verification each time. Marking based positioning was used for the first fraction and new reference surface images were captured after first CBCT registration (6D of freedom,6DoF) for subsequent treatment. Subsequent treatment was randomly divided into marking guided positioning fraction group (MFG) and surface guided positioning fraction group (SFG). In the SFG, the patient was aligned manually by the therapist until the rotation tolerance was within 1°. The residual translation and rotation errors were corrected using the "Move Couch" function of the optical surface system Align RT (Vision RT, London, UK). The six-dimensional error data of patients with the two positioning methods were compared and expressed as mean ± standard deviation. Meanwhile, the correlation and consistency between the optical surface error data and the gold standard CBCT error data were compared during the MFG. A scientific 2D graphing and statistics software was used for data processing and mapping, and a statistical software was used for mean analysis and normality test. Pearson correlation analysis was used to analyze the correlation, and Bland-Altman plot analysis was used to test the coincidence between the two methods. Results Total of 103 MFG CBCT images and 87 SFG CBCT images were analyzed. Compared with the marking guided positioning, the 3D magnitude error of the optical surface guided positioning was reduced from 0.35 ± 0.16 cm to 0.14 ± 0.07 cm and the rotation error was reduced from 0.06° ± 1.36°, 0.62° ± 1.18°, 0.21° ± 1.19° to -0.04° ± 0.68°, -0.03° ± 0.73°, 0.04° ± 0.69° on Pitch, Roll and Rotation. The Pearson coefficient R2 was 0.91,0.70,0.78 on Lateral, Longitudinal and Vertical directions, R2 was 0.75,0.85,0.77 on Pitch, Roll and Rtn directions, respectively (all P Conclusion The optical surface error and cone-beam CT error have good correlation and coincidence. The optical surface guided positioning can reduce the setup errors and the results support the application of 3D surface imaging for image guidance in the hypofractionated radiotherapy for intracranial metastasis with open face mask immobilization.