Simulation study of boron neutron capture radiotherapy using Geant4

<bold>Background</bold>Boron neutron capture therapy (BNCT) is a new binary targeted radiotherapy, and the radiation distribution during the treatment will be affected by neutron energy and boron concentration.<bold>Purpose</bold>This study aims to investigate the influence of neutron energy and boron concentration on BNCT treatment for lung cancer which is of reference significance for the future clinical application.<bold>Methods</bold>Firstly, a computational model for lung cancer treatment based on BNCT was constructed using the Monte Carlo Simulation Toolkit Geant4. The model was surrounded by materials of the entire space from the outside to the inside as air, normal tissue, tissue 1, tissue 2, and lung tumor, with densities of 1.293×10^-3 g∙cm^-3, 1.00 g∙cm^-3, 1.20 g∙cm^-3, 1.30 g∙cm^-3, and 1.40 g∙cm^-3, respectively. Then, by systematically simulating the incident of hyperthermal neutrons (0.5 eV~10 keV) and combining different boron concentration conditions (20 μg∙g^-1, 40 μg∙g^-1, 50 μg∙g^-1, 60 μg∙g^-1, 140 μg∙g^-1), the dose distribution characteristics of secondary particles generated during the BNCT process in lung tumors and surrounding normal tissues were quantitatively analyzed. Then, the dose uniformity of the tumor in the <italic>XY</italic> plane under the same conditions was analyzed. Subsequently, under three total boron concentration conditions in the tumor, the influence of the uneven boron distribution in the tumor area on the radiation dose uniformity of lung tissue plane was compared.<bold>Results</bold>The results demonstrate that the boron dose and γ photon dose increase with the increase of boron concentration, while the dose distribution caused by electrons and protons is not affected by boron concentration, and it is found that the increase of boron concentration can significantly improve the uniformity of tumor irradiation dose. When the boron concentration in lung tissue is constant, compared with thermal neutrons, the boron dose caused by fast neutrons is mainly distributed in deeper tumor tissues, and the neutron energy affects the distribution of proton dose in normal tissues. The higher the neutron energy, the higher the proton dose and the lower electron dose.<bold>Conclusions</bold>It is necessary to comprehensively consider the selection of appropriate neutron energy and boron concentration during the treatment, and the related results provide theoretical reference for clinical BNCT treatment of lung cancer.