Feasibility and Preliminary Validation of 2D/3D Image Registration Using Fixed 2-D X-Ray Devices in Image-Guided Radiotherapy

In radiotherapy, fixed 2-D X-ray imaging devices have several advantages compared to gantry-mounted systems, such as less geometrical deformations and the possibility to monitor 3-D markers motion in real-time. However, there is a lack of studies concerning the geometry of these systems. For example, in the case of a non-orthogonal geometry, the effect of the angle between the X-ray axes has not been investigated yet. In the first part of this study, the optimal angle was analyzed theoretically. Results showed that 60 degrees between the axes still enables displacements of the order of 0.35 mm to be detected. In a second step, the performance of the registration method for such oblique configuration was evaluated on phantom data sets. It was found that using images separated by 60 degrees rather than 90 degrees required more than twice as much the number of iterations to obtain sufficient accuracy (i.e. 0.7 mm and 0.5 degrees).