MONTE-CARLO SIMULATION OF THE BIOLOGICAL EFFECTS OF BORON NEUTRON-CAPTURE IRRADIATION WITH D(14)-VITRO(BE NEUTRONS IN)

It was shown that radiation effects in tumor cells treated with fast n eutrons may be increased by the neutron capture reaction B-10(n,alpha) Li-7. The classic approach for macroscopic dosimetry in fast-neutron t herapy cannot be applied to the dose in boron neutron capture therapy (BNCT). The effectiveness of BNCT in killing tumor cells depends on th e number of B-10 atoms delivered to the tumor, the subcellular distrib ution of B-10 and the thermal neutron fluence at the site of the tumor . Monte Carlo calculations of the energy depositions of short-range pa rticles with high LET coming from B-10 disintegrations were performed and compared to the observed biological effects. The simulation allows us to study the influence of the localization of intracellular B-10 i n the nucleus, cytoplasm, plasma membrane or extracellular space. The biological response function which describes the probability of the le thal effect produced by a single particle track through the cell nucle us was found by comparing the calculated microscopic dose distribution spectra for single events with the survival observed experimentally. Calculations for a human melanoma cell population treated as a monolay er in the presence or absence of boron with d(14)+Be neutrons will be demonstrated. Two different boron compounds enriched in B-10 were inve stigated in this study: boric acid (H-3 (BO3)-B-10) and p-dihydroxybor yl phenylalanine (BPA). The study shows that a high fraction of BPA en ters the cytoplasm while boric acid was found only in the extracellula r space. The computer simulations indicate that BPA yields a higher po tential effectiveness for inactivation of melanoma cells than boric ac id. (C) 1995 by Radiation Research Society