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

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. (authors)