The Comparison of the shares of stopping power in a soft tissue-equivalent material

Abstract

Introduction: Proton therapy is a type of radiation treatment that it uses protons to treat cancer. Because of the protons’ unique ability to distribute the radiation dose more directly to the tumor, it minimizes the damage to nearby healthy tissues. The rate of energy loss by the ion in the target is called stopping power. The total stopping power is sum nuclear and electronic stopping power. Electronic stopping power refers to the slowing down of a projectile ion due to the inelastic collisions between bound electrons in the medium and the ion moving through it. Nuclear stopping power refers to the elastic collisions between the projectile ion and atoms in the target. Materials and Methods: It should be noted that soft tissue-equivalent material denotes a substance, with absorbing and scattering properties for a given radiation that sufficiently match those of a certain biological tissue. The soft tissue-equivalent material usually consists of four elements of hydrogen, oxygen, carbon and nitrogen. By using the SRIM code, we calculated the total stopping power in each element for 10-MeV proton beam. Then, using Bragg's rule, we got the total stopping power for these elements. Also, using the same code, we obtained the total stopping power for the compound. Also, we obtained the contribution of nuclear and electronic stopping power to the total stopping power in this material. Results: By comparing, we observed that the peak height of stopping power using Bragg's rule is more than 20% higher than the SRIM code. This is due to the core and bond (CAB) corrections at low energies in the SRIM code. Also, we observed that total stopping power is due to the electronic stopping power in high energies. By reducing energy, the electronic stopping power is slowly reduced, and the share of nuclear stopping power slowly increases, and the intersection of these is at 50eV energy. Then the contribution of the nuclear stopping power is greater. Conclusion: The proton therapy to treat cancerous tumors is a major technological advance. In low- energies CAB corrections must be taken into account for stopping power of the compound, and therefore, the peak height of the stopping power is reduced. In soft tissue equivalent material for proton beam the contribution of the nuclear stopping power at energies of less than 50 eV is greater than the electronic stopping power. In other energies, the electron- stopping power share is dominant.