Calculation of secondary neutron absorbed dose in spot scanning proton therapy method using GATE simulator

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Abstract

During the proton therapy process, secondary neutrons are produced by the nuclear interactions of protons with the materials in the beam transmission line. In this study, the dose due to the secondary neutrons produced in an RW3 phantom was estimated using Monte Carlo simulation and was compared with the measured values. To do this, the neutron dose due to the collision of proton beams with energies of 100, 150, 200 and 220 MeV with the phantom, was investigated by Bonner sphere detectors and a tissue-equivalent proportional counter for different positions around the phantom vs. proton energy, length spread-out Bragg peak and the dimensions of the treatment field. With increasing energy from 100 to 220 MeV, depending on the position of the detector around the phantom, the dose due to neutron was increased up to 40 times. The effect of increasing the field dimensions from 2×2 to 20×20 cm leads to increase the induced dose up to 40 times for a specific energy. Also, with increasing the length of the spread-out Bragg peak up to 5 cm, a sharp increase in the dose was observed; after 5 cm, the increasing trend stopped and the dose amount did not affect the increase in the length of the Bragg peak spread area.

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