External beam radiotherapy (
EBRT) or
teletherapy is the most common form of
radiotherapy. The patient sits or lies on a couch and an external source of
radiation is pointed at a particular part of the body. In contrast to internal radiotherapy (
brachytherapy), in which the radiation source is inside the body, external beam radiotherapy directs the radiation at the tumour from outside the body. Kilovoltage ("superficial") X-rays are used for treating skin cancer and superficial structures. Megavoltage ("deep") X-rays are used to treat deep-seated tumours (e.g. bladder, bowel, prostate, lung, or brain).