The present invention relates to a determination method for making it possible to determine the position of a body part subject to vital movement that is to be irradiated, by means of determining a region of an analytical image,
wherein the region represents a body part subject to vital movement, in particular a tumor in an anatomical body, and performs a change in position from one analytical image to the next that reflects the vital movement, wherein the body parts subject to vital movement are parts of the body that are to be irradiated or are not to be irradiated and that move as a result of vital functions such as respiration and/or heartbeat even when the anatomical body is otherwise kept deliberately at rest,
advance analytical image data, which includes the description of an advance analytical image having an advance region in which a first body part subject to vital movement is represented, is provided,
procedure analytical image data that includes the description of a procedure analytical image of the body structure is provided,
on the basis of the advance analytical image data and the procedure analytical image data, a procedure region, which corresponds to the advance region and occupies a procedure position in the procedure analytical image, is determined in the procedure analytical image,
wherein a) determination of the procedure position of the procedure region is based on movement data that includes information on the vital movements of the body parts that are caused by the vital functions, and/or b) determination of the position of a second body part subject to vital movement is based on the determined procedure position and information on the relative position between the first and the second body part subject to vital movement.