ISMJ

Background: Generally in radiotherapy via photon, healthy cells can be damage besides cancer cells but in proton therapy these additional harms reach to its minimum. Because, proton deposit its maximum linear energy at the end of its trajectory known as Bragg pick. In this study, efficient range of energy in breast cancer treatment and estimation of secondary particle flux in proton therapy for indicating subsequent cancer risk is considered. Materials and Methods: In this study, at first we have simulated a semi-cylinder compressed breast phantom via MCNPX code and then we applied proton energy with 1MeV step in semi-cylinder phantom. Afterward, we have studied effects of this beam on tumor. Results: The calculations show that the proper energy interval for tumor treatments with a thickness of 6mm with depth of 14 mm from the surface of the breast phantom is 41-48 MeV. In this study, secondary particle flux like neutron and photon with respect to proton initial energy has been calculated. Furthermore, flux diagram of these particle versus energy have been plotted. In neutron flux graph, the neutron spectrum has a significant intensity peak at low energy and flux intensity decreases smoothly as neutron energy increases. Also, in the photon flux spectrum, observed peaks are as a result of excitations in 31P, 12C, 16O nuclei. 12C nuclei produce maximum photon flux. Conclusion: Proton therapy is more precise than conventional radiotherapy and cause less damage to healthy non tumor cells. Because in the useful calculated range of energy, maximum dose or damage is exerted on tumor. However, this treatment method produces secondary particles that maybe damage other cells around the tumor.