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X-ray beam physics 

X-ray beam physics
X-ray beam physics

R Mackay

and A Hounsell

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date: 21 October 2019

In external beam radiotherapy, the radiation originates in a machine some distance from the patient surface. The properties of the X-ray beam depend on what and how the radiation is produced. X-rays are only produced when the ‘beam is on’ and are the result of the collision of accelerated electrons with a target material and thus X-rays are bremsstrahlung radiation. An important determinant of beam energy is the electrical potential through which a beam is accelerated. When an electron is accelerated across a voltage of 50,000V it will acquire energy of 50,000eV and this is the maximum energy that can be transferred to the X-ray produced by the bremsstrahlung interaction of the electron with a target. Often the energy on a treatment machine will be referred to by a kilovoltage (kV) or megavoltage (MV) potential that represents this maximum possible energy: in reality most of the photons will have less energy than this maximum and the spectrum of energies of an X-ray source will have a peak at approximately one third of the maximum (see ...

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