Radiotherapy device comprising a positioning device, and positioning method

A positioning device that controls a position of a treatment couch on which a subject is mounted, the positioning device comprising:

• an image acquisition unit that acquires a plurality of fluoroscopic images obtained by imaging the subject along each of a plurality of imaging axes in a direction different from a plurality of movement axes along which the treatment couch translationally moves;
• a creation unit that creates a plurality of simulated fluoroscopic images obtained by projecting a three-dimensional fluoroscopic image of the subject onto each of a plurality of surfaces corresponding to each imaging axis of the plurality of imaging axes;
• a calculation unit that calculates a similarity between each of the plurality of fluoroscopic images and each of the plurality of simulated fluoroscopic images;
• and
• an optimization unit that calculates, based on the similarity, a movement amount of the treatment couch such that each fluoroscopic image and each simulated fluoroscopic image match most in each of a plurality of translation directions along each of a plurality of optimization axes including the plurality of imaging axes and a plurality of rotation directions around a plurality of rotation axes,
• wherein each rotation axis of the plurality of rotation axes is identical to an optimization axis of the plurality of optimization axes.