Boron neutron capture therapy: re-irradiation response of the rat spinal cord

Purpose: To evaluate the retreatment response of the CNS to BNC irradiation using a rat spinal cord model. Materials and methods, Fischer 344 rats were irradiated with single doses of 6 MeV X-rays which were 22, 40 or 80% of a total effect (TE). An additional group of rats was irradiated with a single exposure of thermal neutrons in the presence of the neutron capture agent boronophenylalanine (BPA) to a dose that represented 82% of the TE. After an interval of 26 weeks, animals were re-irradiated using various single doses of thermal neutrons in combination with BPA. Results: The re-irradiation ED50 doses represented 77, 80 or 50% of the TE after an initial X-ray dose of 22, 40 or 80% of the TE, respectively. The re-irradiation ED50 dose was 55% of the TE after an initial BNC irradiation dose representing 82% of the TE. Conclusion: The level of the initial radiation damage had a direct bearing on the re-irradiation response. Recovery following initial treatment with BNC irradiation was similar to that after initial irradiation with X-rays. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.