Teletherapy
| External beam radiotherapy | |
|---|---|
| Intervention | |
| ICD-10-PCS | [1]?0 |
| ICD-9-CM | 92.21-92.26 |
External beam radiotherapy (EBRT) or teletherapy is the most common form of radiotherapy (radiation therapy). The patient sits or lies on a couch and an external source of ionizing 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. Orthovoltage ("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).
X-rays 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 beams of heavier particles, particularly protons.
Conventionally, the energy of diagnostic and therapeutic gamma- and X-rays is expressed in kilovolts or megavolts (kV or MV), whilst the energy of therapeutic electrons is expressed in terms of megaelectronvolts (MeV). In the first case, this voltage is the maximum electric potential used by a linear accelerator to produce the photon beam. The beam is made up of a spectrum of energies: the maximum energy is approximately equal to the beam's maximum electric potential times the electron charge. Thus a 1 MV beam will produce photons of no more than about 1 MeV. The mean X-ray energy is only about 1/3 of the maximum energy. Beam quality and hardness may be improved by X-ray filters, which improve the homogeneity of the X-ray spectrum.
In the medical field, useful X-rays are produced when electrons are accelerated to a high energy. Some examples of X-ray energies used in medicine are:
Megavoltage X-rays are by far most common in radiotherapy for treatment of a wide range of cancers. Superficial and orthovoltage X-rays have application for the treatment of cancers at or close to the skin surface.
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