Boron neutron capture therapy for malignant brain tumors

Boron neutron capture therapy (BNCT) is tumor-selective particle radiation therapy that depends on the nuclear capture and fission reactions. These reactions occur when a non-radioactive boron isotope (¹⁰B) is irradiated with low-energy thermal neutrons to yield high linear energy transfer α-particles and lithium-7 nuclei within a limited path length, i.e., an almost one-cell diameter. The ¹⁰B-containing cells can then be selectively destroyed by these potent particles. BNCT has been applied in the field of malignant brain tumors for newly diagnosed and recurrent malignant gliomas (chiefly glioblastomas).

These clinical applications of BNCT have been performed with reactor-based neutron sources over the past decades. We also applied reactor-based BNCT for 58 newly diagnosed glioblastomas and 68 recurrent malignant gliomas including 52 glioblastomas. In this review article, we summarize the clinical results from the literature concerning BNCT for these high-grade gliomas (including our research). We also applied reactor-based BNCT for 46 cases of recurrent and refractory high-grade meningiomas, and some of the results will be presented herein.

In Japan, neutron sources have been shifted from reactors to accelerators. Phase 1 and 2 clinical trials have been performed for recurrent malignant gliomas using accelerator-based neutron sources, and now fortunately, a cyclotron-based neutron generator has been approved as a medical device by Japanese regulatory authority, as the world's first accelerator-based BNCT system for medical use. We also discuss the future prospects of accelerator-based BNCT in hospitals as therapy for malignant brain tumors.