[1] Stanford Univ, Dept Radiat Oncol, Sch Med, Stanford, CA 94305 USA
[2] Stanford Univ, Sch Med, Stanford, CA 94305 USA
[3] Stanford Univ, Sch Med, Dept Neurosurg, Stanford, CA 94305 USA
[4] Stanford Univ, Sch Med, Dept Neurol, Stanford, CA 94305 USA