Room: Exhibit Hall | Forum 6
Purpose: To investigate the accuracy of two 3D/3D CT to CBCT registration platforms as well as a 3D/2D CT to X-ray projection registration method. These three technologies are available to perform 6D registrations for image-guided intracranial radiosurgery.
Methods: Eight fiducial markers were asymmetrically placed on the surface of a stereotactic head phantom. The solution for the transformation between the two image sets in rotation and translation was optimized through least-squares fitting of the fiducial positions using singular value decomposition (SVD). This was used as the gold standard to evaluate the rotational accuracy of 3D/3D registration in Varianâ€™s platform, as well as 3D/3D and 3D/2D registration in the BrainLab ExacTrac system. The phantom was setup on a baseplate with all rotations 0 degrees, and 3 degrees in roll and pitch. Measurements of rotational shifts were made at four different intracranial isocenters using the SVD, the 3D/3D and 3D/2D registration methods. Wilcoxon signed-rank test was utilized to compare the difference of each registration method with SVD. A p-value<0.05 was considered significant.
Results: The setup difference between planning CT and CBCT using SVD for all 12 positions showed median and range values of -0.9Â° [1.0Â°,-2.8Â°], -0.3Â° [0.1Â°,-3.3Â°], -1.2Â° [2.8Â°, -2.7Â°] for yaw, pitch, and roll, respectively. Comparing to the SVD measurement, the rotational differences at yaw, pitch, and roll using Varianâ€™s 3D/3D registration were 0.0Â° [0.2Â°, -0.5Â°] (p=0.182), 0.0Â° [0.3Â°,-0.2Â°] (p=0.09), and -0.1Â° [0.2Â°,-0.4Â°] (p=0.73). They were -0.1Â° [0.6Â°,-0.4Â°] (p=0.003), 0.1Â° [0.6Â°,-0.1Â°] (p=0.47), and 0.1Â° [0.5Â°,-0.2Â°] (p=0.52) for ExacTrac 3D/3D registration and -0.4Â° [-0.1Â°,-0.7Â°] (p<0.001), 0.3Â° [0.6Â°,0.0Â°] (p<0.001), and -0.2Â° [0Â°, -0.4Â°] (p<0.001) for ExacTrac 3D/2D registration.
Conclusion: Both 3D/3D rotational registrations were accurate. 3D/2D registration introduced 0.2Â°-0.4Â° rotational inaccuracy in intracranial cases.