A STOCHASTIC-MODEL FOR SUBCELLULAR DOSIMETRY IN BORON NEUTRON-CAPTURETHERAPY

The therapeutic effectiveness of boron neutron capture therapy is high ly dependent on the microscopic distribution of the administered boron compound. Two boron compounds with different uptake mechanisms in the tumour cells may thus cause effects of different degrees even if the macroscopic boron concentrations in the tumour tissue are the same. Th is difference is normally expressed quantitatively by the so-called re lative local efficiency (RLE). In this work, a stochastic model for th e subcellular dosimetry has been developed. This model can be used to calculate the probability for an energy deposition above a certain thr eshold level in the cell nucleus due to a single neutron capture react ion. If a threshold cell-kill function is assumed, and if the dose is low enough that multiple-energy depositions are rare, the model can al so be applied to calculations of the survival probability for a cell p opulation. Subcellular boron distributions in rats carrying RG 2 rat g liomas were measured by subcellular fractionation after administration of two different boron compounds: a sulphydryl boron hydride (BSH) an d a boronated porphyrin (BOPP). Based on these data, the RLE factors w ere then calculated for these compounds using the stochastic model.