Boron neutron capture therapy for brain tumors

Boron neutron capture therapy (BNCT) is a unique method that can provide the delivery of tumor cell-selective high-linear energy transfer (LET) particle radiotherapy to tumor mass and the microscopic invasion while avoiding radiation damage to the surrounding normal brain tissue. The rationale of BNCT is based on the nuclear interaction of ¹⁰B with thermal neutrons with the release of high LET α and ⁷Li particles through the boron neutron capture reaction, ¹⁰B(n, α) 7Li. The very short path length (<9 μμm) of α-particles and ⁷Li enables high-LET irradiation of tumor cells without undesirable damage to ¹⁰B-unloaded normal cells. Eight non-randomized prospective external beam BNCT trials for glioblastoma (GBM) have been performed over the past 15 years using two available boron drugs and neutron beams at the nuclear reactor. The reported median time to progression and the median survival time (MST) are 6-12 and 12-27 mos, respectively. Optimization of dosage and boron delivery agents, the combined use of different boron agents, the combination of BNCT with other therapeutic modalities, and the development of in-hospital accelerator-based neutron sources are underway for the improvement of BNCT. In light of the existing clinical reports, there is a clear need for more evidence-based data.