Orthovoltage X-rays
A 200 kV orthovoltage X-ray tube used for radiation therapy, 1938. Orthovoltage X-ray machines are similar to diagnostic (radiography) X-ray machines, except that higher voltages are used and the X-ray tube is longer, to prevent the high voltages from arcing across the tube. ICD10 =
ICD-992.22
OPS-301 code8-521

Orthovoltage X-rays are produced by X-ray tubes operating at voltages in the 100–500 kV range, and therefore the X-rays have a peak energy in the 100–500 keV range.[1] Orthovoltage X-rays are sometimes termed "deep" X-rays (DXR).[2] They cover the upper limit of energies used for diagnostic radiography, and are used in external beam radiotherapy to treat cancer and tumors. They penetrate tissue to a useful depth of about 4–6 cm.[3] This makes them useful for treating skin, superficial tissues, and ribs, but not for deeper structures such as lungs or pelvic organs.[4] The relatively low energy of orthovoltage X-rays causes them to interact with matter via different physical mechanisms compared to higher energy megavoltage X-rays or radionuclide γ-rays, increasing their relative biological effectiveness. [5]

History

The energy and penetrating ability of the X-rays produced by an X-ray tube increases with the voltage on the tube. External beam radiotherapy began around the turn of the 20th century with ordinary diagnostic X-ray tubes, which used voltages below 150 kV.[6] Physicians found that these were adequate for treating superficial tumors, but not tumors inside the body. Since these low energy X-rays were mostly absorbed in the first few centimeters of tissue, to deliver a large enough radiation dose to buried tumors would cause severe skin burns.[7]

Therefore beginning in the 1920s "orthovoltage" 200–500 kV X-ray machines were built.[8] These were found to be able to reach shallow tumors, but to treat tumors deep in the body more voltage was needed. By the 1930s and 1940s megavoltage X-rays produced by huge machines with 3–5 million volts on the tube, began to be employed. With the introduction of linear accelerators in the 1970s, which could produce 4–30 MV beams, orthovoltage X-rays are now considered quite shallow.[9]

See also

References

  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 978-92-0-107304-4.
  2. ^ Cerry, Pam; Duxbury, Angela (1998). Practical Radiotherapy: Physics and Equipment. London: Greenwich Medical Media. p. 107. ISBN 9781900151061.
  3. ^ Hill, Robin; Healy, Brendan; Holloway, Lois; Kuncic, Zdenka; Thwaites, David; Baldock, Clive (21 March 2014). "Advances in kilovoltage x-ray beam dosimetry". Physics in Medicine and Biology. 59 (6): R183–R231. Bibcode:2014PMB....59R.183H. doi:10.1088/0031-9155/59/6/R183. PMID 24584183.
  4. ^ Hansen, Eric; Roach III, Mack (2007). Handbook of Evidence-based Radiation Oncology. New York: Springer. p. 5. ISBN 9780387306476.
  5. ^ Bell, Brett I.; Vercellino, Justin; Brodin, N. Patrik; Velten, Christian; Nanduri, Lalitha S.Y.; Nagesh, Prashanth K.B.; Tanaka, Kathryn E.; Fang, Yanan; Wang, Yanhua; Macedo, Rodney; English, Jeb; Schumacher, Michelle M.; Duddempudi, Phaneendra K.; Asp, Patrik; Koba, Wade; Shajahan, Shahin; Liu, Laibin; Tomé, Wolfgang A.; Yang, Weng-Lang; Kolesnick, Richard; Guha, Chandan (3 August 2022). "Orthovoltage X-Rays Exhibit Increased Efficacy Compared with γ-Rays in Preclinical Irradiation". Cancer Research. 82 (15): 2678–2691. doi:10.1158/0008-5472.CAN-22-0656. PMC 9354647. PMID 35919990.
  6. ^ Zaidi, Zohra; Walton, Shernaz (2013). A Manual of Dermatology. New Delhi: JP Brothers Medical. p. 872. ISBN 9789350904589.
  7. ^ Khan, Faiz M.; Gibbons, John P. (2014). Khan's The Physics of Radiation Therapy (5th ed.). Philadelphia: Lippincott Williams & Wilkins. p. 41. ISBN 9781469881263.
  8. ^ Linz, Ute (2011). "From X-Rays to Ion Beams: A Short History of Radiation Therapy" (PDF). Ion Beam Therapy. Biological and Medical Physics, Biomedical Engineering. Vol. 320 (1st ed.). Berlin: Springer. p. 6. doi:10.1007/978-3-642-21414-1_1. ISBN 978-3-642-21413-4.
  9. ^ Cognetta, Armand B.; Mendenhall, William M. (2013). Radiation Therapy for Skin Cancer. New York: Springer. p. 33. ISBN 9781461469865.
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