Abstract: A set of surface reference marks (26, 26?) detectable by a surface sensor (4) is disposed on the surface of the subject for acquiring three-dimensional or 3D surface images of the surface of the subject, the surface reference marks being radio-opaque; with each radiological image (3, 3?) acquired is associated a corresponding surface image acquired at substantially the same time; an iterative process includes a phase of incidence angle calculation (10) and a phase of deformation calculation (11), intended to determine (15) the relative positions of the radiological images and the surface images as well as to perform a positioning (16) in the three dimensions of the radiological images by assuming an absence of deformation of the subject, and intended to determine (19) and correct (21) on the radiological images the deformations of the subject for the relative positions determined in the phase of incidence angle calculation.