Background: Whole brain irradiation (WBRT) includes treatment of the whole intracranial compartment (brain and brainstem) down to the foramen magnum or to the bottom of either the first or second cervical vertebrae, and it is a mainstay of treatment in patients with both identifiable brain metastases and prophylaxis for microscopic disease. WBRT has the ability to treat both gross and microscopic disease, preventing the development of new gross metastatic disease and its associated symptoms. The duration of response is highly variable. A relatively high rate of symptom improvement has been demonstrated, with 64–83% of patients benefiting in early studies. Brain irradiation has effects on brain vasculature as well as neuroglial cells and their precursors, including stem cells . In addition, inflammation and blood-brain barrier disruption, induced by radiation, may also cause or enhance direct or indirect cellular damage.