Calculation of the Equivalent Dose of the First and the Most Important Secondary Particles in Brain Proton Therapy by Monte Carlo Simulation

Introduction: Due to nuclear interactions between the tissues and high-energy protons, the particles, including neutrons, positrons, and photons arise during proton therapy. This study aimed at investigating the dose distribution of proton and secondary particles, such as positrons, neutrons, and photons using the Monte Carlo method. Material and Methods: In this study, a beam of protons was utilized with the energies of 160 and 190 MeV, which are more popular for brain tumor treatment. This beam irradiated the brain phantom after passing through proton therapy nozzle components. This phantom has a tumor with a radius of 3 cm in its centre. The most important parts of the nozzle include magnetic wobbler, scatterer, ridge filter, and collimator. Results: The results show that while using protons with the energy values of 190 and 160 MeV, the equivalent dose fractions in tumor, brain, skull, and skin to the total equivalent dose in the head are 61.8 (62.4%), 10.4(10.9%), 6.07(3.69%), and 21.7(23%), respectively, regarding the primary and secondary particles. Conclusion: According to the obtained results, in spite of the fact that most of the equivalent dose was inside the tumor volume, the skin of head has received the noticeable dose during proton therapy of brain which needs more concern.