Figure 3.

The pipeline of reconstructing 4D-CT in the treatment day. First, the free-breathing 3D-CT is roughly aligned with planning day 4D-CT by bone alignment. Then, the mixed phase information in I will be deinterlaced into partial 4D-CT D according to the respiratory motion. Next, 4D-to-4D image registration is performed between the partial 4D-CT D and the complete 4D-CT P to reconstruct the treatment day 4D-CT T by iteratively establishing spatial correspondences on key points, propagating correspondences along the respiratory motion, interpolating the dense deformation field, and adjusting the treatment day respiratory motion.