A Monte Carlo Study on the Effect of Various Neutron Capturers on Dose Distribution in Brachytherapy with (252)Cf Source

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 (10)B, (157)Gd and (33)S neutron capturers and to determine the effect of these materials on dose enhancement rate for (252)Cf 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 (10)B, (157)Gd and (33)S using Monte Carlo simulation. RESULTS: The difference in the thermal neutron flux rate in the presence of (10)B and (157)Gd 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 (157)Gd and (10)B, respectively at about 8 cm distance from the source center. DEF for (33)S is equal to one. CONCLUSION: Results show that the magnitude of dose augmentation in tumors containing (10)B and (157)Gd in brachytherapy with (252)Cf source will depend not only on the capture product dose level, but also on the tumor distance from the source. (33)S makes dose enhancement under specific conditions that these conditions depend on the neutron energy spectra of source, the (33)S concentration in tumor and tumor distance from the source.