Tolerance of canine brain to boron neutron capture therapy.

The normal canine brain tolerance to boron neutron capture therapy (BNCT), with which selective radiotherapy of the brain tumor is expected, was demonstrated by two different series of the irradiation experiment. Normal dogs were irradiated on the skull with thermal neutrons from the reactor after intravenous infusion of 10B-enriched Na2B12H11SH, and the intravascular dose at the brain surface was calculated as the radiation dose. In series 1, the brains of 3 dogs were irradiated 2000 to 3000 rads by the current therapeutic regimen of BNCT and were autopsied after three years observation. In series 2, 6 dogs were given various high doses up to 9000 rads to their brain by BNCT, and autopsied after 1 month and 1 year respectively. Tolerance was excellent in all the dogs, with no unusual findings clinical, neurological, or in laboratory data during the observation period, and no pathological changes by autopsy. When the reduction of the endothelial dose to one third of the intravascular dose and the quick attenuation of thermal neutrons are taken into consideration, the actual doses to the vascular wall in both experiments might be low enough to be tolerated by the normal brain tissue.