Moving-body tracking device for radiation therapy, irradiation region determining device for radiation therapy, and radiation therapy device

An irradiation region determining device for radiation therapy, wherein the irradiation region determining device for a treatment beam is used for a radiation therapy apparatus that treats a patient by irradiating the patient with the treatment beam, comprising:

• a treatment planning acquisition circuit that acquires a shape of a treatment target locus in a reference breathing phase and four-dimensional CT image data consisting of a group of pieces of three-dimensional CT image data of a region including the treatment target locus in multiple successive breathing phases from a storage device;
• a CT image deformation amount calculation circuit that performs image registration on the four-dimensional CT image data acquired from the storage device, and thereby calculate a deformation amount of a three-dimensional CT image including the treatment target locus between different breathing phases;
• a shape calculation circuit that calculates shapes of the treatment target locus in the respective breathing phases on a basis of the shape of the treatment target locus in the reference breathing phase, the shape being acquired from the storage device, and the deformation amount of the three dimensional CT image including the treatment target locus between the different breathing phases, the deformation amount being calculated by the CT image deformation amount calculation circuit;
• and
• an irradiation region determining circuit that determines a treatment beam irradiation region on a basis of the shapes of the treatment target locus in the respective breathing phases, the shapes being calculated by the shape calculation circuit.