The Monte Carlo method is the most accurate method for the simulation of radiotherapy equipment. Linear accelerator (Linac) is currently the most widely used in radiotherapy center's machines. In this work we run the Monte Carlo code EGSnrc under the platform BEAMnrc to calculation of important photon beam parameters by modeling the head of the linear accelerator SATURNE43.The aim of this study was to calculate the dosimetric functions, namely: the dose profile and Percentage depth dose (PDD) for a 12 MV photon beam generated by Linac SATURNE43 and delivered in a water phantom. Photons are generated by the bremsstrahlung effect of electrons during interaction with the tungsten target. All calculations are done by considering a square field dimension 10x10cm