Radiotherapy is a cancer treatment technique that currently occupies an important place in the management of patients. Its challenge is to obtain the best possible compromise between irradiation of the tumor and irradiation of neighboring healthy tissues, which must remain minimal. Optimization of the deposited dose in organs at risk is crucial in radiotherapy treatment. The aim is to emphasize the conformity of lead as a constituent material of the collimator to protect the organs at risk. For this, the demonstration was made on the female pelvic area, which was modeled in the form of a mathematical phantom with real dimensions provided from clinical data, as well as a mobile collimator which makes a rotation of 360° over the phantom, according to the beam axis using the Monte Carlo simulation platform GEANT4. The dose distribution was evaluated based on the values of the Cross-Sections (CS) and Attenuation Coefficients (AC) for photons and electrons, which were calculated using empirical models by the Monte Carlo methods. The dose calculations converge towards the same conclusion with the values of the CS and the AC, which makes it possible to underline the validity and the credibility of the modelization