A method and system of determining a radial distance (R), an angular position (&phgr), and an axial position (Z) of a marker identified in a sequence of projection images. A marker three-dimensional localization module (executable by the electronic processing unit) obtains a sequence of images based on image data generated by a scanner. Each image in the sequence of images represents an angle of rotation by the scanner and includes a marker point position. The behavior of first values and second values of the marker point positions are analyzed through the sequence of images to determine the radial distance of the marker, the angular position of the marker, and the axial position of the marker allowing for rapidly detecting and localizing external markers placed on a patient in projection images.
