Dose point kernel for boron-11 decay and the cellular S values in boron neutron capture therapy

Abstract

The study of the radiobiology of boron neutron capture therapy is based on the cellular level dosimetry of boron-10's thermal neutron capture reaction 10B (n,α)7Li, in which one 1.47 MeV helium-4 ion and one 0.84 MeV lithium-7 ion are spawned. Because of the chemical preference of boron-10 carrier molecules, the dose is heterogeneously distributed in cells. In the present work, the (scaled) dose point kernel of boron-11 decay, called B11 11-DPK, was calculated by GEANT4 Monte Carlo simulation code. The DPK curve drops suddenly at the radius of 4.26 μm, the continuous slowing down approximation (CSDA) range of a lithium-7 ion. Then, after a slight ascending, the curve decreases to near zero when the radius goes beyond 8.20 μm, which is the CSDA range of a 1.47 MeV helium-4 ion. With the DPK data, S values for nuclei and cells with the boron-10 on the cell surface are calculated for different combinations of cell and nucleus sizes. The S value for a cell radius of 10 μm and a nucleus radius of 5 μm is slightly larger than the value published by Tung [Appl. Radiat. Isot. 61, 739-743 (2004)]. This result is potentially more accurate than the published value since it includes the contribution of a lithium-7 ion as well as the alpha particle. © 2006 American Association of Physicists in Medicine.