Radiobiological evaluation of the 10B(n,α)7Li reaction and its efficacy in neutron capture therapy

The boron neutron capture reaction [10B(n,α)7Li] is, in principle, very effective in destroying a tumor, provided that a sufficient amount of boron can be accumulated in the target tissue. The two particles generated in this event have a high linear energy transfer (LET) and a short range of about one cell diameter. Several methods of accumulating boron via physiological pathways are currently being explored in numerous laboratories. In most cases, boron is conjugated to a tumor-seeking substance, like antibodies, amino acids, porphyrins, etc. The radiobiological efficacy of the boron neutron capture reaction and its modulation by different geometric arrangements of boron in relation to the radiation-sensitive part of the cell is very important for the amount of boron that has to accumulate in the target cells. The energy deposition in the nucleus of cells exposed to the 10B(n,α)7Li neutron capture reaction has been calculated by means of Monte Carlo methods. Events were simulated randomly in space and compared to the biological effect of this reaction, which has been measured before in V79 Chinese hamster cells. There, a D0 value of 0.66 Gy was found. Thus, a certain average dose deposited in the cell nucleus would lead to a certain amount of cell killing. Boron was also located in a given spatial arrangement relative to the cell nucleus. Such an arrangement might be obtained with some the above boron carriers currently under investigation