Methods and devices are disclosed for treating a patient with an unruptured saccular aneurysm that is not associated with an arteriovenous malformation, wherein ionizing radiation is delivered to the brain of a patient through stereotactic radiosurgery. The radiosurgery may be performed with a Gamma Knife stereotactic radiosurgery apparatus, LINAC device such as CYBERKNIFE® stereotactic radiosurgery apparatus, or particle-beam device. The treatment impedes a natural progression of the aneurysm towards rupture and may actually obliterate the aneurysm. The treatment plan may be based in part on measured geometric properties of the aneurysm or on physical aneurysm properties such as permeability, wall thickness, wall motion, the presence of macrophages, shear stress, and flow velocities. The methods may be used in conjunction with endovascular coil embolization.