A method of performing microbeam radiation therapy (MRT) includes delivering a dose only to selected tissue in a target volume (10) with continuous broad beam, first, by interleaving arrays of microplanar beams (30,36) only at the target (10). Administered contrast agents can supplement the effect by preferentially increasing the target dose relative to dose in normal tissue. A broad beam effect is alternatively created using non-interleaving microbeam array(s) with scattering agents administered to selected tissue that preferentially increase valley dose (69) within target to approximate broad beam. The methods of interleaving microbeams are also applied to treat diseases and conditions by ablating at least a portion of selected tissue, or by damaging blood-brain barrier for efficient drug and/or cell administration. A system for performing interlaced microbeam radiosurgery preferably includes two orthogonal radiation source arms (102) for producing and interleaving microbeam arrays (30,36) at the target volume (10). The methods treat tumors, pain, epilepsy, and neurological diseases.
STATEMENT OF GOVERNMENT LICENSE RIGHTS
 This invention was made with Government support under contract number DE-AC02-98CH10886, awarded by the U.S. Department of Energy. The Government has certain rights in the invention.