MODEL RELEASED. Gamma knife radiotherapy. Patient undergoing gamma knife radiotherapy. This is usually used in the treatment of brain tumours. The patient receives a single dose of gamma radiation, delivered through the ports of a collimator helmet (top centre). 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. The therapy 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.