Breast cancer is the most common type of cancer in women. Today, the radiotherapy method is widely preferred to treat cancer patients where proton therapy is a radiotherapy method used to destroy cancerous cells using proton beams with unique characteristics. Photon therapy, on the other hand, is a classical radiotherapy method that treats cancerous cells by targeting ionizing radiation. In our study, a tumor was placed in the left breast in a water phantom with the help of the Geant4 simulation program and geometry with critical organs was modeled. With this simulation, the doses received by the organs were interpreted and comparisons were made using the chi-square method as the two different source beams, proton and photon deployed. When the percentile values in the dose table are normalized for 1 Gy, the test statistic obtained as 0.467, and the H0 hypothesis is rejected at the α=0.975 Statistically, we measured the significant differences between proton and photon dose values for tumors and other organs by Geant4 simulations.