A HISTORY OF BORON NEUTRON-CAPTURE THERAPY OF BRAIN-TUMORS - POSTULATION OF A BRAIN RADIATION-DOSE TOLERANCE LIMIT

Boron neutron capture therapy (BNCT) is a form of radiation therapy mediated by the short-range (less than 10-mu-m) energetic alpha (He-4) and lithium-7 (Li-7) ionizing particles that result from the prompt disintegration by slow neutrons of the stable (nonradioactive) nucleus boron-10 (B-10). Recent advances in radiobiological and toxicological evaluation of tumour-affinitive boron-containing drugs and in optimization of the energies of neutrons in the incident beam have spurred interest in BNCT. This article presents a history of BNCT that emphasizes studies in the USA. A new dosimetric analysis of the 1959-1961 clinical trials of BNCT at Brookhaven National Laboratory is also presented. This analysis yields an acute radiation dose tolerance limit estimate of approximately 10 Gy-Eq to the capillary endothelium of human basal ganglia from BNCT. (Gy-Eq: Gray-equivalent, or relative biological effectiveness of a radiation component multiplied by the physical dose of the component (Gy), summed over the component kinds of radiation.)