Our primary research interest centers on medical imaging science, particularly for applications to image-guided radiation therapy (IGRT). In modern radiation therapies, accurate images of the treatment target before/during/after the treatment are particularly important to increase the tumor control probability and to reduce the normal tissue complication probability. Recent advances in image reconstruction techniques for cone-beam computed tomography (CBCT) have spurred research in applications of the new techniques to IGRT. We also investigate algorithms for new radiotherapeutic approaches.