1. A therapy-planning system comprising: a planning system configured to generate a therapy plan for delivery of therapy to a target region of a patient using a first image received from at least one imaging modality; a therapy delivery apparatus configured to deliver the therapy to the target region; one or more registration processors programmed to: receive the first image and a second image received from at least one imaging modality, identify corresponding interest points in the first image and the second image, identify corresponding structures in the first image and the second image, identify boundaries of the identified corresponding structures, fit corresponding mesh models to the identified boundaries of the corresponding structures of the first image and the second image in one or more regions in which a density of corresponding interest points is below a threshold, select corresponding vertices of the mesh models in the first image and the second image as the corresponding boundary points, generate a registration map from the corresponding interest points and a plurality of the corresponding boundary points using point based registration; wherein the planning system is further configured to update the therapy plan based on the registration map; and a therapy control system configured to control the therapy delivery system to deliver the therapy in accordance with the updated therapy plan.