‎Amir Veiskarami - Department of Medical Radiation Engineering‎, ‎Science and Research Branch‎, ‎Islamic Azad University‎, ‎Tehran‎, ‎Iran
‎Mahdi Sadeghi - Iran University of Medical Sciences‎, ‎Medical Physics Department‎, ‎Tehran‎, ‎Iran
‎Dariush Sardari - Department of Medical Radiation Engineering‎, ‎Science and Research Branch‎, ‎Islamic Azad University‎, ‎Tehran‎, ‎Iran
‎Shahryar Malekie - Radiation Application Research School‎, ‎Nuclear Science & Technology Research Institute‎, ‎PO Box ۳۱۴۸۵-۴۹۸‎, ‎Karaj‎, ‎Iran

‎Collision of protons with background gas and beamline wall in proton therapy causes the creation of secondary particles‎, ‎e.g. neutrons‎, ‎which results in more difficulties in curing the tumors‎. ‎In the present simulation-based study‎, ‎the optimum diameter of proton beamline was determined to minimize the production of secondary particles in the presence of electric field with the magnitude of 50 kV/m‎, ‎perpendicular equal magnetic fields of 0.7 T‎, ‎and background gas of argon under Bounce boundary conditions via finite element method‎. ‎The results showed that the optimum diameter of the beamline for minimization of the secondary particles in the spot scanning proton therapy in the aforementioned conditions was 7 mm‎. ‎Also‎, ‎the values of drift velocities of protons were plotted in different time steps of 10 ns to 50 ns for the optimized size of the beamline‎. ‎Due to few interactions of forwarding particles with background gas‎, ‎the results showed that the forwarding particles in the propagation direction have greater velocities than those of rear particles‎. ‎The results can be used in spot scanning proton therapy for curing the localized cancers‎.

‎Spot Scanning Proton Therapy, ‎Beamline Diameter, ‎Secondary Particles, ‎Finite Element Method‎