Abstract: Irradiation treatment can be used before, during, or after a surgical treatment or other injury to the brain to decrease or prevent subsequent injury. Injury to the brain during surgery can induce the infiltration of peripheral immune cells, including splenic immune cells, into the brain. The infiltration of immune cells can create acute elevations in brain edema and blood-brain barrier disruption thereby decreasing neurological recover and patient outcomes. Irradiation of peripheral immune cells, or the region of the body in which the cells are derived, can allow for inactivation of the cells and prevent infiltration into the surgical site, for example, the brain.