Fig. 1.

BNCT is based on the nuclear capture and fission reactions that occur when boron-10, a nonradioactive constituent of natural elemental boron, is irradiated with low-energy (0.025 eV) thermal neutrons or, alternatively, higher-energy (10,000 eV) epithermal neutrons, which lose energy as they penetrate tissues and become thermalized. This capture reaction results in the production of high linear energy transfer (LET) alpha particles (⁴He) and recoiling lithium-7 (⁷Li) nuclei (Fig. 1a). In order to be successful, a sufficient amount of ¹⁰B must be selectively delivered to the tumor (~ 20–50 µg/g or ~ 10⁹ atoms/cell) (Fig. 1b) and a collimated beam of neutrons (Fig. 1c) must be absorbed by the tumor (Fig. 1d) to sustain lethal damage from the ¹⁰B(n,α)⁷Li capture reaction. The destructive effects of the alpha particles are limited to boron-containing cells and, because they have very short pathlengths in tissues (5–9 µm), BNCT provides a way to selectively destroy malignant cells and spare surrounding normal tissue, making it, in theory, an ideal type of radiation therapy