external beam radiotherapy

(redirected from External beam radiotherapy or teletherapy)
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external beam radiotherapy

treatment by radiation emitted from a source located at a distance from the body. Also called beam therapy, external beam therapy.


the treatment of disease by ionizing radiation. The purpose of radiation therapy is to deliver an optimal dose of either particulate or electromagnetic radiation to a particular area of the body with minimal damage to normal tissues. The source of radiation may be outside the body of the patient (external radiation therapy) or it may be an isotope that has been implanted or instilled into abnormal tissue or a body cavity. Called also radiation therapy.
Modern radiation therapy primarily uses high-energy x-rays or gamma rays with peak photon energies above 1 MeV. This is called 'supervoltage' or 'megavoltage' therapy. These high voltages are produced by linear accelerators or by cobalt-60 teletherapy units. Megavoltage radiation is more penetrating than lower energy radiation. It produces less damage to the skin at the entry port, is absorbed less in bone, and is scattered less, thus reducing the exposure to tissues outside the x-ray beam. Low-energy x-rays that do not penetrate are used for treatment of superficial skin lesions.
Internal radiation therapy can involve the implantation of sealed radiation sources in or near cancerous tissue. Isotopes, such as radium-226, cesium-137, iridium-192 and iodine-125, are introduced either temporarily or permanently into body tissues (interstitial application) or body cavities (intercavitary application). Permanent sources have a short half-life so that the dose received by the patient is limited. Another form of internal radiation therapy is the administration of radioactive materials into the bloodstream or a body cavity.
See also radiation, external beam therapy, orthovoltage, brachytherapy.

external beam radiotherapy
fractionated radiotherapy
the full dose is divided and given as a number of separate small treatments.
intraoperative radiotherapy
the use of radiotherapy during a surgical procedure, usually in the treatment of diffuse neoplasia that cannot be totally removed by surgical methods alone.
supervoltage radiotherapy, megavoltage radiotherapy
the use of energy in excess of 500 keV.
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