External beam radiotherapy otherwise known as teletherapy, is the most frequently used 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. Kilovoltage (also known as, superficial) x-rays are used for treating skin cancer and superficial structures. Megavoltage (or deep) X-rays are used to treat deep-seated tumours (eg bladder, bowel, prostate, lung, brain).
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External beam radiotherapy otherwise known as teletherapy, is the most frequently used 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. Kilovoltage (also known as, superficial) x-rays are used for treating skin cancer and superficial structures. Megavoltage (or deep) X-rays are used to treat deep-seated tumours (eg bladder, bowel, prostate, lung, brain).
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...
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