The present invention focuses on an analytical model for fast and accurate scatter estimation. The present invention uses the Klein-Nishina (KN) formula as a starting point, which gives the Compton scattering differential cross-section for an interaction point. For a direct integration of the point scatter kernel over the irradiated volume, the large number of KN formulae (e.g., amount of solid angle subtended) and rays traced required for calculating attenuation makes the computation very expensive. The present invention reduces the 3D formulation into an efficient 2D approach by integrating the KN formula along an interaction line of tissue-equivalent medium. An average attenuation length was assumed for each interaction point on the beam to reduce the number of rays traced. In the case of kilovoltage (kV) x rays as the imaging source and a small imaging field, with in-field scatter, the line integral derived, can be approximated by a compact analytical form.
