A method for tracking a target located within a body, whilst scanning the body using X-ray projections, the method including the steps of: (a) providing a first prior image of the body and target indicating their relative position； (b) iteratively performing, for a series of time intervals, the steps of: (i) acquiring a few spatially distributed x-ray projections of the target area； (ii) determining one of a series of motion phases for each x-ray projection； (iii) performing an iterative reconstruction of the image for each of the motion phases； and (iv) outputting a resultant image for a current time interval.
