Megavoltage X-rays are produced by

linear accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear ...

s ("linacs") operating at

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

s in excess of 1000 kV (1 MV) range, and therefore have an

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

in the

MeV In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt in vacuum. When us ...

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. They are used in medicine in

external beam radiotherapy External beam radiation therapy (EBRT) is a form of radiotherapy that utilizes a high-energy collimated beam of ionizing radiation, from a source outside the body, to target and kill cancer cells. The radiotherapy beam is composed of particl ...

to treat

neoplasm A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

and

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

s. Beams with a voltage range of 4-25 MV are used to treat deeply buried cancers because

radiation oncologist A radiation oncologist is a specialist physician who uses ionizing radiation (such as megavoltage X-rays or radionuclides) in the treatment of cancer. Radiation oncology is one of the three primary specialties, the other two being surgical an ...

s find that they penetrate well to deep sites within the body. Lower energy x-rays, called

orthovoltage X-rays 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. Orthovoltage X-rays are sometimes termed "deep" X-rays (DXR). They ...

, are used to treat cancers closer to the surface. 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. Megavoltage X-rays also have lower

relative biological effectiveness In radiobiology, the relative biological effectiveness (often abbreviated as RBE) is the ratio of biological effectiveness of one type of ionizing radiation relative to another, given the same amount of absorbed energy. The RBE is an empirical ...

than orthovoltage x-rays. These properties help to make megavoltage x-rays the most common beam energies typically used for radiotherapy in modern techniques such as IMRT.

History

The use of megavoltage x-rays for treatment first became widespread with the use of Cobalt-60 machines in the 1950s. However prior to this other devices had been capable of producing megavoltage radiation, including the 1930s

Van de Graaff generator A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate electric charge on a hollow metal globe on the top of an insulated column, creating very high electric potentials. It produces very high voltage direct ...

and

betatron A betatron is a type of cyclic particle accelerator for electrons. It consists of a torus-shaped vacuum chamber with an electron source. Circling the torus is an iron transformer core with a wire winding around it. The device functions simil ...

References

{{Radiation oncology Radiation therapy X-rays

History

See also

References