Introduction: Proton therapy is newer therapeutic method for early stage breast cancer. Proton beams release most of their energy in the Bragg peak and then will be a rapid decline in their end. When protons interact with matter, produce secondary particles like neutrons and gammas, and these unwanted radiation has no beneficial effect and also is believed to increase the risk of secondary cancers, so it’s necessary to assess these secondary particles. Monte Carlo algorithm is the most accurate calculation method in the dosimetry. MCNPX is a modern, general purpose Monte Carlo code that were used to model the transport and interactions of particles in patient’s body, also is currently the most commonly used MC codes for proton therapy. In this study, calculated flux of secondary particles like neutron and photon in vital organs and dose distribution of Proton in energy range of 40 to 70 with 10 single step.
Materials and Methods: Analytical phantom of the human body, ORNL used to create the input files and Protons as pencil beam modeled in front of left breast with energy of 40 to 70 MeV for covering the left breast, eventually Counting sensors for tracking the trajectory of secondary particles and provide the necessary data were used.
Results: the dose distribution of protons shows they can have covered the exact shape of tumor with high accuracy and release most of their energy on it, so it’s best feature of proton therapy also flux of secondary particles shows the most important organs are Heart-left ventricle and left lung in left breast proton therapy because of the most flux of secondary particles reach to them.
Conclusion: flux of secondary particles in vital organs shows that even though proton therapy is a good option Due to the favorable Bragg peak radiation and delivers high dose to a small volume of cancerous tissue while the healthy structures will be spared during proton radiation therapy and flux of secondary particles are low but they are not low enough to be negligible.