Physics:Megavoltage X-rays

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Short description: High energy (>1MeV) X-rays
Megavoltage X-rays
Megavolt x-ray machine - Los Angeles Inst of Radiology 1938.jpg
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

Megavoltage X-rays are produced by linear accelerators ("linacs") operating at voltages in excess of 1000 kV (1 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.[1] They are used in medicine in external beam radiotherapy to treat neoplasms, cancer and tumors. Beams with a voltage range of 4-25 MV are used to treat deeply buried cancers because radiation oncologists find that they penetrate well to deep sites within the body.[2] Lower energy x-rays, called orthovoltage X-rays, are used to treat cancers closer to the surface.[3]

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.[4][5][6] Megavoltage X-rays also have lower relative biological effectiveness than orthovoltage x-rays.[7] These properties help to make megavoltage x-rays the most common beam energies typically used for radiotherapy in modern techniques such as IMRT.[8]


The Use of megavoltage x-rays for treatment first became widespread with the use of Cobalt-60 machines in the 1950s.[9] However prior to this other devices had been capable of producing megavoltage radiation, including the 1930s Van de Graaff generator and betatron.[10][11][12]

See also


  1. Podgorsak, E B (2005). "Treatment Machines for External Beam Radiotherapy". Radiation Oncology Physics: A Handbook for Teachers and Students. Vienna: International Atomic Energy Agency. p. 125. ISBN 92-0-107304-6. 
  2. Camphausen KA, Lawrence RC. "Principles of Radiation Therapy" in Pazdur R, Wagman LD, Camphausen KA, Hoskins WJ (Eds) Cancer Management: A Multidisciplinary Approach. 11 ed. 2008.
  3. Herrmann, Joerg (2016) (in en). Clinical Cardio-oncology. Elsevier Health Sciences. p. 81. doi:10.1016/B978-0-323-44227-5.00003-X. ISBN 9780323462396. 
  4. Buzdar, SA; Rao, MA; Nazir, A (2009). "An analysis of depth dose characteristics of photon in water.". Journal of Ayub Medical College, Abbottabad 21 (4): 41–5. PMID 21067022. 
  5. Sixel, Katharina E. (1999). "Buildup region and depth of dose maximum of megavoltage x-ray beams". Medical Physics 21 (3): 411. doi:10.1118/1.597305. Bibcode1994MedPh..21..411S. 
  6. Pazdur, Richard (2005). "Principles of radiation therapy". Cancer management : a multidisciplinary approach : medical, surgical, & radiation oncology (9th ed., 2005-2006. ed.). New York: Oncology Group. ISBN 9781891483356. 
  7. Amols, H. I.; Lagueux, B.; Cagna, D. (January 1986). "Radiobiological Effectiveness (RBE) of Megavoltage X-Ray and Electron Beams in Radiotherapy". Radiation Research 105 (1): 58. doi:10.2307/3576725. Bibcode1986RadR..105...58A. 
  8. Levitt, Seymour H. Levitt; Purdy, James A; Perez, Carlos A; Poortmans, Philip (2012). "Physics of Radiotherapy Planning and Delivery". Technical basis of radiation therapy practical clinical applications (5th ed.). Heidelberg: Springer. p. 96. ISBN 9783642115721. 
  9. Robison, Roger F. (8 July 2009). "The Race For Megavoltage X-Rays Versus Telegamma". Acta Oncologica 34 (8): 1055–1074. doi:10.3109/02841869509127233. 
  10. Halperin, Edward C; Perez, Carlos A; Brady, Luther W (2008). Perez and Brady's principles and practice of radiation oncology (5th ed.). Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. p. 150. ISBN 9780781763691. 
  11. Trump, John G.; van de Graaff, R. J. (15 June 1939). "A Compact Pressure-Insulated Electrostatic X-Ray Generator". Physical Review 55 (12): 1160–1165. doi:10.1103/PhysRev.55.1160. Bibcode1939PhRv...55.1160T. 
  12. Kerst, D. W. (February 1943). "The Betatron". Radiology 40 (2): 115–119. doi:10.1148/40.2.115.