optimization of beamline diameter in spot scanning proton therapy for minimization of secondary particles using finite element method

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.