Tracking target position detection device, radiotherapy system, and tracking target position detection method

A tracking target position detection device for detecting a position of a tracking target, the tracking target position detection device comprising:

• one or more sets of digital radiography devices including a fluoroscopy radiation detector and a fluoroscopy radiation generation device as one set and configured to capture a digital radiography image including the tracking target;
• and
• a calculation device configured to obtain the position of the tracking target from the digital radiography image obtained by the digital radiography device, wherein
• the calculation device
• evaluates priority of visibility of the tracking target among a plurality of the digital radiography images of the tracking target,
• calculates a weight distribution representing relative presence accuracy of the tracking target in a low-visibility digital radiography image using epipolar geometry and a difference in the visibility among the digital radiography images, and
• determines a detection position of the tracking target in the low-visibility digital radiography image using the weight distribution and a similarity distribution of the low-visibility digital radiography image.