Abstract: An arrangement in a gamma unit, comprising a large number of radiation sources (9) mounted within a radiation shield (2) and having beam channels (6, 19) directed radially from said radiation sources toward a common focal point (F), said radiation shield comprising a space adapted to accommodate the head of a patient resting on a support.The novel matter resides in that the radiation sources (9) and the beam channels (6, 19) directed radially therefrom toward the focal point are located, in relation to the diametrical plane through the opening to the space, within a zone extending to latitudes 30.degree.-45.degree., as seen from said diametrical plane.