External beam radiotherapy 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).
While X-ray and electron beams are by far the most widely used sources for external beam radiotherapy, a small number of centers operate experimental and pilot programs employing heavier particle beams, particularly proton sources.
Read more about External Beam Radiotherapy: Photons, Electrons, Hadron Therapy, Multi-leaf Collimator, Intensity Modulated Radiation Therapy, Image-guided Radiation Therapy
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