Reconstructing Dynamic Magnification CBCT Scans with Optimization-Based Reconstruction

In image guided radiation therapy (IGRT), certain patient treatment positions can lead to collisions of the patient with the linac gantry. When such collisions arise, it prevents the gantry from rotating around the patient and acquiring sufficient projection information for current analytic-based reconstruction methods such as FDK. One way to alleviate such a collision would be to move the patient or imaging arms at the offending gantry position changing the magnification. In this work, we investigate if optimization-based reconstruction methods can reconstruct from data acquired from such dynamic-magnification trajectories. Using real data from Varian's TrueBeam 2.0 kV imaging system, we found that these methods can reconstruct from trajectories where different magnifications are used in a single scan. This suggests these optimization-based reconstruction methods have the potential to enable collision avoiding imaging trajectories, improving patient comfort and reducing the costly clinical delays that currently arise from these collisions.