ABSTRACT
BACKGROUND: The amount of average dose enhancement in tumor loaded with 10B may vary due to various factors in boron neutron capture therapy. OBJECTIVE: This study aims to evaluate dose enhancement in tumor loaded with 10B under influence of various factors and investigate the dependence of this dose enhancement on neutron spectra changes. MATERIAL AND METHODS: In this simulation study, using 252Cf as a neutron source, the average in-tumor dose enhancement factor (DEF) and neutron energy spectra were calculated for various 10B concentrations, phantom with different sizes and for different tumor locations, through MCNPX code. RESULTS: Obtained results showed that the values of average DEF rise with increasing 10B concentration, phantom diameter (Ë 30 cm) and tumor distance from the source, but this increment is not linear. CONCLUSION: It was concluded that inequality in average dose enhancement rates, in tumor loaded with 10B under influence of various factors in boron neutron capture therapy, is due to non-identical changes of both the thermal neutron flux with increasing same number of 10B atoms and same thickness of scattering material, and the thermal to fast neutron flux ratio with increasing equal distances of tumor from the source.
ABSTRACT
BACKGROUND: In neutron interaction with matter and reduction of neutron energy due to multiple scatterings to the thermal energy range, increasing the probability of thermal neutron capture by neutron captures makes dose enhancement in the tumors loaded with these materials. OBJECTIVE: The purpose of this study is to evaluate dose distribution in the presence of 10B, 157Gd and 33S neutron capturers and to determine the effect of these materials on dose enhancement rate for 252Cf brachytherapy source. METHODS: Neutron-ray flux and energy spectra, neutron and gamma dose rates and dose enhancement factor (DEF) are determined in the absence and presence of 10B, 157Gd and 33S using Monte Carlo simulation. RESULTS: The difference in the thermal neutron flux rate in the presence of 10B and 157Gd is significant, while the flux changes in the fast and epithermal energy ranges are insensible. The dose enhancement factor has increased with increasing distance from the source and reached its maximum amount equal to 258.3 and 476.1 cGy/h/µg for 157Gd and 10B, respectively at about 8 cm distance from the source center. DEF for 33S is equal to one. CONCLUSION: Results show that the magnitude of dose augmentation in tumors containing 10B and 157Gd in brachytherapy with 252Cf source will depend not only on the capture product dose level, but also on the tumor distance from the source. 33S makes dose enhancement under specific conditions that these conditions depend on the neutron energy spectra of source, the 33S concentration in tumor and tumor distance from the source.
