RADIATION EFFECTS OF BORON NEUTRON-CAPTURE THERAPY ON BRAIN, SKIN, AND EYE OF RATS

Purpose: The present study was carried out to evaluate the radiation e ffects of boron neutron capture therapy (BNCT) on the brain, skin, and eyes of nude rats following systemic administration of boronophenylal anine (BPA) and neutron irradiation to the head. Methods and Materials : A solution containing 120 mg of B-10-enriched-L-BPA complexed with f ructose was administered IP to nude rats. Boron concentrations were si milar to 8.4, 9.4, 10.0, and 11.0 mu g/g in the brain, blood, skin, an d eyes, respectively, at 6 h when the animals were irradiated at the B rookhaven Medical Research Reactor (BMRR). As determined in a study ca rried out in parallel with this one, the BNCT radiation doses were suf ficient to cause tumor regression in nude rats carrying intracerebral implants of the human melanoma cell line MRA 27. Results: Mild to mode rate increases in loose fibrous tissue were observed in the choroid pl exus at estimated physical doses to the brain and blood that ranged fr om 4.3-7.1 Gy and 4.6-7.7 Gy, respectively, and these appeared to be d ose and time dependent. Other changes in the choroid plexus included o ccasional infiltrates of macrophages and polymorphonuclear leukocytes and vacuolation of epithelial cells. Dose-dependent moist desquamation of the skin was observed in all rats, but this had healed by 28 days following irradiation. Cataracts and keratitis developed in the eyes o f most animals, and these were dose dependent. Conclusion: The minimal histopathological changes seen in the brain at doses that were suffic ient to eradicate intracerebral melanoma indicates that BNCT has the p otential to cure a tumor bearing host without producing the normal bra in injury usually associated with conventional external beam radiation therapy. Studies in canines, which currently are in progress, should further define the dose-effect relationships of BNCT on critical neuro anatomic structures within the brain.