RÉSUMÉ
Objective:To evaluate the accuracy of the optical surface imaging system (OSI) using stereotactic radiosurgery (SRS) algorithm in single-center non-coplanar treatment of multiple brain metastases.Methods:Data of phantom and 15 patients with multiple brain metastases who underwent single-center non-coplanar radiotherapy in West China Hospital of Sichuan University from February to April 2022 were retrospectively analyzed. kV/MV and OSI imaging were used for imaging of the patients and phantoms under the same non-coplanar couch angle, respectively. The accuracy of OSI imaging of the phantoms and patients was evaluated using kV/MV imaging as reference image. The difference between the OSI and kV/MV systems is defined as accuracy, and the percentage of the absolute difference ≤1.00 mm in the translational direction or ≤0.50° in the rotational direction is defined as the threshold pass rate. Origin software was used to draw radar maps and Bland-Altman plots for statistical analysis.Results:When OSI images were used for the phantom imaging, the average differences in six-dimensional directions of lateral, long, vertical, rotational, roll and pitch were 0.03 mm, -0.09 mm, -0.27 mm, 0.04°, 0.17° and -0.19°, respectively. The maximum values were -2.20 mm, -2.30 mm, -1.20 mm, 0.60°, -1.00°, and -1.00°, respectively. When OSI system was utilized for the imaging of 15 patients, the average differences in six-dimensional directions were 0.44 mm, 0.16 mm, -0.20 mm, -0.11°, 0.10°, and -0.12°, respectively. The maximum values were -1.80 mm, 2.00 mm, 0.90 mm, -0.90°, -0.70°, and 0.80°, respectively. The translational errors mainly occurred in the lateral and long directions. The qualified rates of the threshold values of the phantoms and patients were 77% and 75% in the lateral direction, 82% and 89% in the long direction, respectively. In addition, 57% and 56% of patients met the threshold conditions of ±1.00 mm and ±0.50° in the six-dimensional directions, respectively.Conclusions:The OSI system using new SRS algorithm cannot meet the high accuracy requirements of single-center non-coplanar radiotherapy for multiple brain metastasis, especially in the lateral and long directions. It is not recommended for non-coplanar image guidance.