Radiotherapy, the treatment of disease using ionizing radiation, is mainly associated with cancer treatment but is - to a limited extent - also used for the treatment of some non-malignant diseases. In external beam radiotherapy, radiation beams originating externally to the patient are directed towards the treatment site. These beams are usually created through the use of a linear accelerator or a cobalt unit. In brachytherapy, small and encapsulated radioactive sources are placed directly into or near the volume to be treated. Endovascular brachytherapy, finally, is used for prevention of restenosis in arteries following coronary arterial angioplasty.