The program at Donner Pavilion has applied nuclear medicine research to the diagnosis and radiosurgical treatment of life-threatening intracranial vascular disorders that affect approximately one million Americans. Stereotactic heavy-ion Bragg peak radiosurgery, using narrow beams of heavy ions (helium), demonstrates superior biological and physical characteristics in brain over X and gamma rays and protons, viz., improved dose distribution in the Bragg peak, sharp lateral and distal borders, and less multiple scattering and range straggling for the same residual range in CNS tissue. Examination of CNS tissue response and alteration of cerebral blood-flow dynamics related to heavy-ion Bragg peak radiosurgery is being undertaken using three-dimensional treatment planning and quantitative imaging utilizing cerebral angiography, computerized tomography (CT), magnetic resonance imaging (MRI), cine-CT, xenon X-ray CT, and positron emission tomography (PET). Also under examination are the physical properties of narrow heavy-ion beams for improving methods of dose delivery and dose distribution and for establishing clinical RBE/LET and dose-response relationships for human CNS tissues. Based on the evaluation and treatment with stereotactically directed narrow beams of heavy ions of over 130 patients, with cerebral angiography and CT scanning, and with MRI and radioisotope scanning of selected patients, plus extensive clinical and neuroradiological follow-up, it appears that heavy-ion radiosurgery obliterates intracranial arteriovenous malformations or protects against rebleeding with reduced morbidity and mortality.