MODEL RELEASED. Gamma knife radiation therapy. Patient undergoing gamma knife radiotherapy. This is usually used to treat brain tumours. The patient receives a single dose of gamma radiation, delivered through the ports of a collimator helmet. The head is held in place by a metal frame. Radiation is targeted at a specific area of the brain and has a minimal effect on surrounding areas. It is non-invasive and provides access to areas of the brain that cannot be reached by other techniques. Photographed at the Gamma Knife Centre, Erasme Hospital, Brussels, Belgium.