The analysis of fast pattern Cone beam CT for thorax and abdomen radiotherapy

Objective: To compare and analyze the difference of setup errors associated with radiotherapy for thorax and abdomen cancer with Cone beam CT (CBCT) between standard scan pattern and fast scan pattern, and to investigate the feasibility of online calibration in fast scan pattern for radiotherapy of thorax and abdomen cancer. Methods: A total of 50 patients with thorax and abdomen cancer were selected and all the patients were designated either clockwise standard CBCT scan and anticlockwise fast CBCT scan before first volumetric modulated arc therapy (VMAT) either. The images of two scan patterns and the setup error of thorax and abdomen cancer were also compared. A physician, a physicists and a technician evaluated the quality of all images using the mean opinion score (MOS) method. Results: The deviation between setup error from standard imaging pattern and setup error from fast imaging pattern of x, y, z axis translation and rotation were (0.2 ± 0.2), (-0.6 ± 0.4), (-0.2 ± 0.3) mm and (0.2 ± 0.1)°, (0.0 ± 0.1)°, (0.1 ± 0.1)°, which was not statistically significant (P > 0.05). The setup error from standard imaging pattern and setup error from fast imaging pattern were highly correlated with statistical significance (r = 0.92-0.98, P < 0.01). The two types of imaging models had satisfactory consistency (Kappa = 0.82-0.94). The average score results of MOS in standard and fast imaging pattern were 3.9, 4.1, 3.8 and 3.6, 4.0, 3.8, respectively, and the differences were not statistically significant (P > 0.05). Conclusions: Fast imaging pattern has high correlation and consistency with the standard imaging model in the CBCT setup error correction, and the quality of images has no significant deterioration. The CBCT fast imaging pattern could be chosen to determine the setup error using online calibration for imaging thorax and abdomen cancer. (authors)