This thesis presents the results of an investigation of the use of collimators in proton therapy. The problem to solve is that in the proton therapy, we do not have the certainty if the target-tumor is receiving all the energy to destroy it or if we are really shooting at this one, so the remaining question is: where the beam is hitting? How to know it? to answer those questions our work has the propose of study proton therapy to determine where the proton interactions occur, these kinds of interactions usually produce gamma rays, and we simulated in GEANT4 the gamma production of a radial source interacting with a collimator made of lead, so our study focused on getting characteristic of the detected gammas and relate those characteristics to a location of the gamma source. The detector was placed behind the collimator, as shown in chapter 4. Each simulation of GEANT4 captured the signal in the detector and this information was analyzed with the program ROOT CERN, providing us the signal in regions of the detector to suggest some characteristics of a detector device. The results obtained are simulations for the number of gammas obtained as a function of the position along the detector, the previous was repeated for different configurations of the detector and different positions of the gamma source, as shown in chapter 5.