PROBLEM TO BE SOLVED: To provide a radiotherapy system including a positioning system capable of shortening a time required for alignment between a region or area, which serves as a reference for positioning and is depicted in an image, and a therapeutic object region or area during image alignment used for radiotherapy.SOLUTION: In a positioning system 104, a feature quantity concerning a position of a region of interest, which is delineated by a therapy planning device 101, is computed for each of a therapy planning CT image and a three-dimensional tomographic image produced for bed positioning. Machine learning using the feature quantities as weak discriminators is carried out. Further, a region or area that should be aligned and a degree (weight) of alignment are obtained. An evaluation formula for positioning which uses the region or area and weight obtained through the learning is created and used to perform positioning.
