Implications of radiation microdosimetry for accelerator-based boron neutron capture therapy: a radiobiological perspective

Abstract

Boron neutron capture therapy (BNCT) has great potential to selectively destroy cancer cells while sparing surrounding normal cells. The basic concept of BNCT was developed in the 1930s, but it has not yet been commonly used in clinical practice, even though there is now a large number of experimental and translational studies demonstrating its marked therapeutic potential. With the development of neutron accelerators that can be installed in medical institutions, accelerator-based BNCT is expected to become available at several medical institutes around the world in the near future. In this commentary, from the point of view of radiation microdosimetry, we discuss the biological effects of BNCT, especially the underlying mechanisms of compound biological effectiveness. Radiobiological perspectives provide insight into the effectiveness of BNCT in creating a synergy effect in the field of clinical oncology.

Figure 1.

BNCT with the intravenous injection of ¹⁰B-BPA. The ¹⁰B-BPA delivery agents are introduced into the patient intravenously and then taken up by tumor cells through amino acid transporters. An epithermal neutron beam is applied, resulting in the ¹⁰B(n,α) ⁷Li reaction within the tumor cells, which selectively destroys the tumor cells. ¹⁰B-BPA; ¹⁰B-boronophenylalanine; BNCT, boron neutron capture therapy.

Figure 2.

Monte-Carlo simulation for dose distribution at the subcellular scale. (a) An example of Monte-Carlo simulation geometry including 25 tumor cells illustrated by the PHITS code. (b) Spatially heterogenous dose distribution for 19 tumor cells taking up ¹⁰B-BPA into the cell cytoplasm and six cells without ¹⁰B compound. The diameters of the cells’ nucleus and cytoplasm were defined as 10 µm and 20 µm, respectively. Thermal neutrons following the spectrum reported by Ceballos et al were transported in the z-axis direction. The cut-off energies of the neutrons and other radiation particles in PHITS were set to 0.1 eV and 1.0 keV, respectively. ¹⁰B-BPA; ¹⁰B-boronophenylalanine; PHITS, Particle and Heavy Ion Transport code System.