An image fusion method which is used for medical applications. The method includes: (a) acquiring a first image with a planned radiation region; (b) acquiring a second image with actual radiation region; (c) determining if user defined landmarks have been placed on the first and second images, if user defined landmarks are present go to step (d), if not go to step (e); (d) pre-transforming the first image or second image or both images; and (e). performing a first delineation step on the actual radiation region. The method further includes: (f) determining if the delineation is correct, if yes go to step (g), if not go to step (h); (g) fusing the first and second image and exit process; and (h) selecting multiple guide points around the actual radiation region in the second image, wherein the guide points are position adaptable points; which are placed near but not on the boundaries of the region; and (i) performing a second delineation step on the actual radiation region and go to step (f).