Positioning apparatus and method of positioning

A positioning method, that performs a positioning for a subject when a therapeutic beam of an irradiation element of a radiography system is irradiated to an affected area of said subject on a therapy table, comprising the steps of:

• obtaining a 2-dimensional radiograph in two different radiography directions of said subject by said radiography system and a radiation detector;
• generating a DRR of said subject in two different directions by reconstructing a geometric arrangement of said radiography system in a virtual space and performing a virtual fluoroscopic projection on CT data collected in advance;
• and
• positioning said CT data and said radiograph so that an evaluation function that evaluates a matching degree between said radiograph in the two different radiography directions and said DRR is at a maximum;
• wherein said positioning step, further comprises the steps of:
• optimizing parameters in a multidimensional optimization step relative to a rotation and a translation corresponding to a moving axis of said therapy table in said fluoroscopic projection of said CT data;
• and relative to a 1-dimensional optimization element that optimizes parameters relative to 1-dimensional translation along the radiography direction of the radiography system, and
• optimizing parameters in a 1-dimensional optimization step relative to 1-dimensional translation along a radiography direction of said radiography system.