Analysis of the setup errors and residual errors for ExacTrac X-ray image-guidance system for radiotherapy of somal tumors

Abstract

Objective To retrospectively analyze the setup error in radiotherapy of somal tumors and body metastases using the ExacTrac X-ray portal image, and to evaluate the feasibility and effectiveness of 6D setup error correction in body radiotherapy. Methods The translational and rotational setup errors were calculated by registering the bony structures on the ExacTrac X- setup images to that of the digitally reconstructed setup images, and the corresponding residual errors were calculated together. Results The translational and rotational setup errors in the x (left-right), y (superior-inferior), z (anterior-posterior) and Rx (sagittal), Ry (transverse), Rz (coronal) directions were(2.27±2.02)mm, (4.49±2.52)mm, (2.27±1.37) mm and (1.02±0.73)°, (0.67±0.68)°, (0.76±0.84)°, respectively. The residual translational and rotational setup errors in the x(r), y(r), z(r) and Rx(r), Ry(r), Rz(r) directions were(0.27±0.48)mm, (0.37±0.45)mm, (0.22±0.30)mm and (0.17±0.33)°, (0.14±0.34)°, (0.16±0.28)°respectively. Conclusions Besides the translational setup errors, a certain amount of rotational setup errors exist in radiotherapy of somal tumors and body metastases. By using the 6D setup error correction of the ExacTrac system, a translational less than 0.4 mm and rotational setup errors less than 0.2° could be achieved. Key words: ExacTrac X-ray image-guidance system; 6 degree-of-freedom treatment couch; Setup errors; Residual errors