In this paper, an Energy Intensity Distribution (EID) model considering dose latitude for Variable Shaped Beam (VSB) has been developed. η values (i.e. back-scattering ratio) versus dose and process threshold have been investigated by using the EID model. Additionally, a new procedure to find optimum PEC values (η) taking into account of the process threshold is proposed through simulation. For fogging effect correction, we have adopted a Gauss model and created a new simulation algorithm to find the most suitable parameters regarding η value, process threshold, dose and the EID model.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.