A method to reconstruct intra-fractional liver motion in rotational radiotherapy using linear fiducial markers.

In this study, we developed a Six Degree of Freedom Projection Marker Matching method (6-DoF PM3) to reconstruct translational and rotational liver tumor motion in a rotational treatment delivery, such as volumetric modulated arc therapy (VMAT). Specifically, we modeled the use of two gold markers implanted in a linear form. The four endpoints of the two gold linear markers were used as tracking surrogates. During delivery, kV x-ray projection images were acquired. A method was developed to automatically identify the 2D marker-endpoints on the projection images. To determine marker positions in 3D, we formulated an optimization problem. The objective function penalized the distance from the reconstructed 3D position of each fiducial marker endpoint to the corresponding straight line defined by the kV x-ray projection of the endpoints. Rigid translational and rotational motion of the liver tumor and motion smoothness along the temporal dimension were assumed. The optimization model was solved via a heuristic two-step alternating direction optimization approach. We performed a series of tests to evaluate different components of the method. For 2D marker endpoints identification, 95.6% of the marker endpoints were identified with an error ≦0.776mm along both u and v directions. For 3D reconstruction of motion in simulation studies, error of rotational angle was (0.5±6.5)×10-3degree without considering the 2D marker identification error. In the experimental end-to-end tests, ...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research