Radiothérapie externe

External beam radiation therapy (EBRT) is a compound word that refers to the use of a collimated beam of ionizing radiation from outside the body to treat a disease. external—from outside the body, beam—shaped by collimation, radiation—ionizing radiation, therapy—used to treat disease The word teletherapy has the same meaning as external beam radiation therapy with the tele- empahasizing that it is treatment from a distance. Radiation and therapy are commonly shortened into the portmanteau radiotherapy. Many classifications are applied to radiotherapy. Teletherapy is the first of four classes of radiotherapy, as grouped by treatment distance. teletherapy—treatment from a distance plesiotherapy—treatment from the surface, i.e. contact therapy brachytherapy—treatment from within, using a sealed source inside the body radiopharmaceutical therapy—treatment from within, using an unsealed source, that mingles with the body, so that the body becomes the source A radiotherapy beam is composed of particles which travel in a consistent direction, i.e. they travel as a group. Each radiotherapy beam is composed of one type of particle which is intended for treatment, though most beams contain some contamination by other particle types. Radiotherapy beams are classified by the particle they are intended to deliver. photons x-rays gamma rays electrons protons neutrons heavy ions As individual photons, x-rays and gamma rays are indistinguishable. The distinction is semantic in that photons created in the nucleus are called gamma rays while those created by electrons are called x-rays. Both are used in radiotherapy. X-rays created by orbital electrons are called characteristic X-ray and though useful in medical imaging characteristic x-rays do not play any significant role in teletherapy. A gamma rays beam is distinguished from a therapeutic x-ray beam by its energy spectrum. Gamma rays are emitted at discrete energies while therapeutic x-rays form a continuous energy spectrum. Teletherapy is the most common form of radiotherapy (radiation therapy).