DOSIMETRIC CONSEQUENCES OF B-10(N,ALPHA)LI-7 REACTION OCCURRING AT THE CELLULAR MEMBRANE

Purpose: Microdosimetric expectations of Boron contents are extracted from a CRAY-Monte Carlo simulation of the nuclear reaction B-10(n,alph a)Li-7 as it occurs on a boronated membrane of a model cell and as the reaction fragments (alpha and Li) traverse into the cellular nucleus. Methods and Materials: The present microdosimetry calculation is base d upon the assumption that the therapeutic advantage of boron neutron capture therapy (BNCT), while depending upon the RBE and LET of the re action particles, is equally dependent on the boron carrier preferenti al localization to tumor tissue, and the boron selectivity to cancerou s cells and its specificity within subcellular compartments. In partic ular, boron fixes to cell membrane as it ought to, using monoclonal an tibodies. The present Monte Carlo simulation computes stochastic expec tations of alpha/Li energy depositions to the nucleus in a uniformly b oronated membrane shell of a spherical cell. Differential energy gain was deduced from the stochastic energy depositions in events of neutro n reactions with membrane boron compared against those with natural el ements (O, H, N) in the cell. Results: Microdosimetry data are present ed in terms of specific energy (keV/mu(3)) and lineal energy (keV/mu) functions of the nucleus-to-cell volume ratios (NCVR). When folded wit h the geometric boron content and accounting for background reaction e nergies, the distributions yield effective energy gain to the cell nuc leus per neutron capture event. Boron amount required to yield these e nergy gains are found to be of the order of picograms of boron per gra m of cell mass. Conclusion: The boron content as inferred by the prese nt Monte Carlo microdosimetry compares well with that deliverable by p resent pharmacokinetic means, but are orders of magnitude (mu-grams) l ess than those deduced previously from anthropomorphic macrodosimetry.