کوروش قیصری

The goal of radiation therapy is to eliminate cancerous cells, so that the tumor receives sufficient dose of ionizing radiation, while at the same time sparing the surrounding normal tissue from as much dose as possible. These beams produce ions in tissue that is very active and can break the DNA strands and cause the death of cancer cells. These two goals have been the motivation for the progression of Hadron Therapy. In hadron therapy, patient receive radiation from an external source with particle like proton or ions, such as helium, carbon, or oxygen. In this study, treatment with proton is studied. Absorption dose of proton is sharp and in a specific area that is very useful for cancer treatment. The proton range depends on the initial energy of the proton and the characteristics of the environment. As a result, tissue inhomogeneities effect the proton path and Bragg peak. In this research, first Snyder head phantom is simulated by using GEANT4 simulation code and then selecting the appropriate energy spectrum to cover the entire tumor, after that weighting coefficients for each energy were obtained by solving linear equations in the MATLAB program and appropriate SOBP was made. In addition, in order to investigate effect of inequality of the skull tissue, the radiation of the skull tissue from three directions (right side of the head, above the head and back) is studied, Also the proton absorption dose and secondary particles such as neutrons and photons in the tissue have been calculated. Simulation results show that about 99% of proton-absorbed dose absorbed in the tumor and less than one percent in the healthy tissue, and the presence of different skull thicknesses can be offset by changing the initial energy of proton beam. if a brain tumor is located in the center of the skull, irradiation is more appropriate from the right side of the head, and also if the tumor be closer to the surface, the greater the dose delivered to tumor and the less dose delivered