Editing Megavoltage X-rays

{{Use American English|date = February 2019}}
{{Short description|High energy (>1MeV) X-rays}}
{{Infobox medical intervention |
  Name        = Megavoltage X-rays |
  Image       = File:Megavolt x-ray machine - Los Angeles Inst of Radiology 1938.jpg |
  Caption     = Early megavolt x-ray machine installed at Los Angeles Institute of Radiotherapy, 1938. Before linacs, high voltage x-ray tubes ''(left column)'' powered by million volt transformers ''(right column)'' were used to produce penetrating x-rays|
  image_size   = 140px|
  ICD10       = |
  ICD9unlinked = {{ICD9proc|92.24}} |
  MeshID      = |
  OPS301      = |
  OtherCodes  = |
}}

'''Megavoltage X-rays''' are produced by [[linear accelerator]]s ("linacs") operating at [[voltage]]s in excess of 1000&nbsp;[[Volt|kV]] (1&nbsp;MV) range, and therefore have an [[energy]] in the [[MeV]] range. The voltage in this case refers to the voltage used to accelerate electrons in the linear accelerator and indicates the maximum possible energy of the photons which are subsequently produced.<ref>{{cite book|last1=Podgorsak|first1=E B|title=Radiation Oncology Physics: A Handbook for Teachers and Students|date=2005|publisher=International Atomic Energy Agency|location=Vienna|isbn=92-0-107304-6|page=125|url=http://www-pub.iaea.org/books/iaeabooks/7086/Radiation-Oncology-Physics-A-Handbook-for-Teachers-and-Students|chapter=Treatment Machines for External Beam Radiotherapy}}</ref>  They are used in medicine in [[external beam radiotherapy]] to treat [[neoplasm]]s, [[cancer]] and [[tumor]]s.   Beams with a voltage range of 4-25 MV are used to treat deeply buried cancers because [[radiation oncologist]]s find that they penetrate well to deep sites within the body.<ref>Camphausen KA, Lawrence RC. [http://www.cancernetwork.com/cancer-management-11/chapter02/article/10165/1399960 "Principles of Radiation Therapy"] in Pazdur R, Wagman LD, Camphausen KA, Hoskins WJ (Eds) [http://www.cancernetwork.com/cancer-management-11/ Cancer Management: A Multidisciplinary Approach]. 11 ed. 2008.</ref>  Lower energy x-rays, called [[orthovoltage X-rays]], are used to treat cancers closer to the surface.<ref>{{cite book|last1=Herrmann|first1=Joerg|title=Clinical Cardio-oncology|date=2016|publisher=Elsevier Health Sciences|isbn=9780323462396|page=81|url=https://books.google.com/books?id=KWtjDQAAQBAJ&pg=PT81|language=en|doi=10.1016/B978-0-323-44227-5.00003-X}}</ref>

Megavoltage x-rays are preferred for the treatment of deep lying tumours as they are attenuated less than lower energy photons, and will penetrate further, with a lower skin dose.<ref>{{cite journal|last1=Buzdar|first1=SA|last2=Rao|first2=MA|last3=Nazir|first3=A|title=An analysis of depth dose characteristics of photon in water.|journal=Journal of Ayub Medical College, Abbottabad|date=2009|volume=21|issue=4|pages=41–5|pmid=21067022}}</ref><ref>{{cite journal|last1=Sixel|first1=Katharina E.|title=Buildup region and depth of dose maximum of megavoltage x-ray beams|journal=Medical Physics|date=1999|volume=21|issue=3|pages=411|doi=10.1118/1.597305|bibcode=1994MedPh..21..411S}}</ref><ref>{{cite book|last1=Pazdur|first1=Richard|title=Cancer management : a multidisciplinary approach : medical, surgical, & radiation oncology|date=2005|publisher=Oncology Group|location=New York|isbn=9781891483356|edition=9th ed., 2005-2006.|chapter=Principles of radiation therapy}}</ref> Megavoltage X-rays also have lower [[relative biological effectiveness]] than orthovoltage x-rays.<ref>{{cite journal|last1=Amols|first1=H. I.|last2=Lagueux|first2=B.|last3=Cagna|first3=D.|title=Radiobiological Effectiveness (RBE) of Megavoltage X-Ray and Electron Beams in Radiotherapy|journal=Radiation Research|date=January 1986|volume=105|issue=1|pages=58|doi=10.2307/3576725|bibcode=1986RadR..105...58A}}</ref> These properties help to make megavoltage x-rays the most common beam energies typically used for radiotherapy in modern techniques such as [[IMRT]].<ref>{{cite book|last1=Levitt|first1=Seymour H. Levitt|last2=Purdy|first2=James A|last3=Perez|first3=Carlos A|last4=Poortmans|first4=Philip|title=Technical basis of radiation therapy practical clinical applications|date=2012|publisher=Springer|location=Heidelberg|isbn=9783642115721|page=96|edition=5th|chapter=Physics of Radiotherapy Planning and Delivery}}</ref>

==History==
The use of megavoltage x-rays for treatment first became widespread with the use of [[Cobalt therapy|Cobalt-60 machines]] in the 1950s.<ref>{{cite journal|last1=Robison|first1=Roger F.|title=The Race For Megavoltage X-Rays Versus Telegamma|journal=Acta Oncologica|date=8 July 2009|volume=34|issue=8|pages=1055–1074|doi=10.3109/02841869509127233|doi-access=free}}</ref> However prior to this other devices had been capable of producing megavoltage radiation, including the 1930s [[Van de Graaff generator]] and [[betatron]].<ref>{{cite book|last1=Halperin|first1=Edward C|last2=Perez|first2=Carlos A|last3=Brady|first3=Luther W|title=Perez and Brady's principles and practice of radiation oncology|date=2008|publisher=Wolters Kluwer Health/Lippincott Williams & Wilkins|location=Philadelphia|isbn=9780781763691|page=150|edition=5th}}</ref><ref>{{cite journal|last1=Trump|first1=John G.|last2=van de Graaff|first2=R. J.|title=A Compact Pressure-Insulated Electrostatic X-Ray Generator|journal=Physical Review|date=15 June 1939|volume=55|issue=12|pages=1160–1165|doi=10.1103/PhysRev.55.1160|bibcode=1939PhRv...55.1160T}}</ref><ref>{{cite journal|last1=Kerst|first1=D. W.|title=The Betatron|journal=Radiology|date=February 1943|volume=40|issue=2|pages=115–119|doi=10.1148/40.2.115}}</ref>

==See also==
* [[Orthovoltage X-rays]]
* [[External beam radiotherapy]]

==References==
<references/>

{{Radiation oncology}}

[[Category:Radiation therapy]]
[[Category:X-rays]]