Show Summary Details
Page of

X-ray beam physics 

X-ray beam physics
Chapter:
X-ray beam physics
Author(s):

R Mackay

and A Hounsell

DOI:
10.1093/med/9780199573356.003.0074
Page of

PRINTED FROM OXFORD MEDICINE ONLINE (www.oxfordmedicine.com). © Oxford University Press, 2016. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Medicine Online for personal use (for details see Privacy Policy and Legal Notice).

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 ...

Access to the complete content on Oxford Medicine Online requires a subscription or purchase. Public users are able to search the site and view the abstracts for each book and chapter without a subscription.

Please subscribe or login to access full text content.

If you have purchased a print title that contains an access token, please see the token for information about how to register your code.

For questions on access or troubleshooting, please check our FAQs, and if you can't find the answer there, please contact us.