BORON NEUTRON-CAPTURE IRRADIATION OF THE RAT SPINAL-CORD - HISTOPATHOLOGICAL EVIDENCE OF A VASCULAR-MEDIATED PATHOGENESIS

A histopathological study was carried out on the spinal cord of rats a fter boron neutron capture (BNC) irradiation. Rats were irradiated wit h thermal neutrons alone or in combination with borocaptate sodium (BS H) or p-boronophenylalanine (BPA). Spinal cords were examined 1 year a fter irradiation, or at earlier times in rats developing myelopathy. C onsidered overall, the pathology of the spinal cord after BNC irradiat ion was comparable with that reported previously after X irradiation o f the spinal cord in the identical strain of rat. When BSH was used as the neutron capture agent, the biologically effective dose of radiati on delivered to the CNS parenchyma was a factor of similar to 2.7 lowe r than that delivered to the vascular endothelium. In effect, the bloo d vessels were selectively irradiated using this BNC modality. The res ultant pathology was similar to that observed after irradiation with t hermal neutrons alone or in the presence of BPA, situations in which t he CNS vasculature was not selectively irradiated. This points to the vascular endothelium as being the critical target cell population, dam age to which results in the development of the lesions seen in the spi nal cord after BNC irradiation and, by inference, after irradiation wi th more conventional modalities. (C) 1996 by Radiation Research Societ y