A method for determining a position of a moving target, comprising: obtaining a first image (302; 702) of the moving target (312; 712), the target being an anatomical feature of a patient, the first image being obtained using a radiation source at a first operative position; obtaining a second image (304; 704a) of the moving target (314; 714a), the second image being obtained using a radiation source at a second operative position different from the first operative position, wherein the first and the second images have different image planes and are generated at different times; processing the first and second images to determine whether the target (312; 712) in the first image (302; 702) corresponds spatially with the target (314; 714a) in the second image (304; 704a); and determining the position of the moving target based on a result of the act of processing, characterised in that the act of processing the first and second images comprises: determining a first line (322; 722) that extends from the source, at the first operative position of the source, and intersects the first image of the target in the image plane of the first image (302; 702); and determining a second line (324; 724a) that extends from the source, at the second operative position of the source, and intersects the second image of the target in the image plane of the second image (304; 704a); and determining a first distance (330; 730a) between the first and second lines. obtaining a first image (302; 702) of the moving target (312; 712), the target being an anatomical feature of a patient, the first image being obtained using a radiation source at a first operative position; obtaining a second image (304; 704a) of the moving target (314; 714a), the second image being obtained using a radiation source at a second operative position different from the first operative position, wherein the first and the second images have different image planes and are generated at different times; processing the first and second images to determine whether the target (312; 712) in the first image (302; 702) corresponds spatially with the target (314; 714a) in the second image (304; 704a); and determining the position of the moving target based on a result of the act of processing, characterised in that the act of processing the first and second images comprises: determining a first line (322; 722) that extends from the source, at the first operative position of the source, and intersects the first image of the target in the image plane of the first image (302; 702); and determining a second line (324; 724a) that extends from the source, at the second operative position of the source, and intersects the second image of the target in the image plane of the second image (304; 704a); and determining a first distance (330; 730a) between the first and second lines. determining a first line (322; 722) that extends from the source, at the first operative position of the source, and intersects the first image of the target in the image plane of the first image (302; 702); and determining a second line (324; 724a) that extends from the source, at the second operative position of the source, and intersects the second image of the target in the image plane of the second image (304; 704a); and determining a first distance (330; 730a) between the first and second lines.