Selective ablation of rat brain tumors by boron neutron capture therapy.

Abstract

Damage to the surrounding normal brain tissue limits the amount of radiation that can be delivered to intracranial tumors. Boron neutron capture therapy (BNCT) is a binary treatment that allows selective tumor irradiation. This study evaluates the damage imparted to the normal brain during BNCT or x-irradiation. The brains of rats with implanted 9L gliosarcomas were examined 1 year after tumor-curative doses of either 250 kV X rays or BNCT. Histopathologic techniques included hematoxylin and eosin staining, horseradish peroxidase perfusion, and electron microscopy. Longterm X ray survivors showed extensive cortical atrophy, loss of neurons, and widespread leakage of the blood-brain barrier (BBB), particularly around the tumor scar. In contrast, the brains and the BBB of longterm BNCT survivors appeared relatively normal under both light- and electron-microscopic examination. Intact blood vessels were observed running directly through the avascular, collagenous tumor scar. The selective therapeutic effect of BNCT is evident in comparison to x-irradiation. Both groups of animals showed no evidence of residual tumor at 1 year. However, with x-irradiation there is no therapeutic ratio and tumor eradication severely injures the remaining brain parenchyma. These observations indicate a substantial therapeutic gain for BNCT.