External beam radiotherapy otherwise known as teletherapy, is the most frequently used form of radiotherapy. The patient sits or lies on a couch and an external source of radiation is pointed at a particular part of the body. Kilovoltage (also known as Superficial or Deep) x-rays are used for treating skin cancer and superficial structures. Megavoltage X-rays are used to treat deep-seated tumours (eg bladder, bowel, prostate, lung, brain). Megavoltage electrons are mainly used for treating superficial tumours. Radiation therapy (or radiotherapy) is the medical use of ionizing radiation as part of cancer treatment to control malignant cells (not to be confused with radiology, the use of radiation in medical imaging and diagnosis). ... Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ...

Photons

Conventionally, the energy of diagnostic and therapeutic gamma- and X-rays is expressed in kilovolts or megavolts (kV or MV), whilst the energy of therapeutic electrons is expressed in terms of megaelectronvolts (MeV). In the first case, this voltage is the maximum electric potential used by a linear accelerator to produce the photon beam. The beam is made up of a spectrum of energies: the maximum energy is approximately equal to the beam's maximum electric potential times the electron charge. Thus a 1 MV beam will produce photons of no more than about 1 MeV. The mean X-ray energy is only about 1/3 of the maximum energy. Beam quality and hardness may be improved by special filters, which improve the homogeneity of the X-ray spectrum. This article is about electromagnetic radiation. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... The volt is the SI derived unit for electric potential and voltage (derived from the ampere and watt). ... In electronics or physics, a megavolt is 1 million volts. ... An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ... A Linear particle accelerator is an electrical device for the acceleration of subatomic particles. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...

In the medical field, useful X-rays are produced when electrons are accelerated to a high energy. Some examples of X-ray energies used in medicine are:

• diagnostic X-rays - 20 to 50 kV
• superficial X-rays - 50 to 200 kV
• orthovoltage X-rays - 200 to 500 kV
• supervoltage X-rays - 500 to 1000 kV
• megavoltage X-rays - 1 to 25 MV

Of these energy ranges, megavoltage X-rays are by far most common in radiotherapy. Orthovoltage X-rays do have limited applications, and the other energy ranges are not typically used clinically. Superficial X-rays are low energy X-rays that do not penetrate very far before they are absorbed. ... Orthovoltage X-rays have an energy in the range of 200-500 kV. When used to treat patients, radiation oncologists find that they penetrate to a useful depth of about 4-6cm. ... Megavoltage X-rays are produced by linear accelerators (linacs) operating at voltages in the 1000+ kV (1+ MV) range, and therefore have an energy in the MeV range (see External beam radiotherapy for an explanation of the maximum and mean energies as a function of voltage). ...

Medically useful photon beams can also be derived from a radioactive source such as cobalt-60, iridium-192, caesium-137 or radium-226 (which is no longer used clinically). Such photon beams, derived from radioactive decay, are more or less monochromatic and are properly termed gamma rays. The usual energy range is between 300 keV to 1.5 MeV, and is specific to the isotope. wikipedia sucks big balls For other uses, see Cobalt (disambiguation). ... This article is about the chemical element. ... Caesium-137 is a radioactive isotope which is formed mianly by nuclear fission (half life is about 27 years). ... General Name, Symbol, Number radium, Ra, 88 Chemical series alkaline earth metals Group, Period, Block 2, 7, s Appearance silvery white metallic Standard atomic weight (226) g·mol−1 Electron configuration [Rn] 7s2 Electrons per shell 2, 8, 18, 32, 18, 8, 2 Physical properties Phase solid Density (near r. ... Something which is monochromatic has a single color. ... This article is about electromagnetic radiation. ...

Therapeutic radiation is mainly generated in the radiotherapy department using the following equipment:

1. Orthovoltage units. These are also known as "deep" and "superficial" machines depending on their energy range. Orthovoltage units have essentially the same design as diagnostic X-ray machines. These machines are generally limited to less than 600 kV.
2. Linear accelerators ("linacs") which produce megavoltage X-rays. Commercially available medical linacs produce X-rays and electrons with an energy range from 4 MeV up to around 25 MeV. The X-rays themselves are produced by the rapid deceleration of electrons in a target material, typically a tungsten alloy, which produces an X-ray spectrum via bremsstrahlung radiation. The shape and intensity of the beam produced by a linac may be modified or collimated by a variety of means. Thus, conventional, conformal, intensity-modulated, tomographic, and stereotactic radiotherapy are all produced by specially modified linear accelerators.
3. Cobalt units which produce stable, dichromatic beams of 1.17 and 1.33 MeV, resulting in an average beam energy of 1.25 MeV. The role of the cobalt unit has partly been replaced by the linear accelerator, which can generate higher energy radiation. Cobalt treatment still has a useful role to play in certain applications and is still in widespread use worldwide, since the machinery is relatively reliable and simple to maintain compared to the modern linear accelerator.

Orthovoltage X-rays have an energy in the range of 200-500 kV. When used to treat patients, radiation oncologists find that they penetrate to a useful depth of about 4-6cm. ... A Linear particle accelerator is an electrical device for the acceleration of subatomic particles. ... Megavoltage X-rays have an energy range of greater than 1,000,000 electron volts (1000 keV, or 1 MeV). ... General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Standard atomic weight 183. ... (help· info), (from the German bremsen, to brake and Strahlung, radiation, thus, braking radiation), is electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. ...

Electrons

X-rays are generated by bombarding a high atomic number material with electrons. If the target is removed (and the beam current decreased) a high eneregy electron beam is obtained. Electron beams are useful for treating superficial disease because they deposit a uniform dose near the surface, which then decreases rapidly with depth, sparing underlying tissue. An energy in the range 6-9MeV is typically used. In water this gives a practical range of 3-4.5cm. Energies above 18MeV are used very rarely.

Multi-Leaf Collimator (MLC)

A MLC collimators consists of 2 sets of leafs, each with 20-40 leafs. Newer MLC's now have up to 120 individual leafs. MLC allows radiographers to match the shape of the tumour, thus minimize the amount of healthy tissue being treated.

Intensity Modulated Radiation Therapy (IMRT) to reduce damage to healthy tissue

IMRT is an advance radiotherapy the technique to minimize the amount of normal tissue being irradiated in the treatment field. (Hayden Wall sucks big penises, and likes it)

Image-Guided Radiation Therapy (IGRT) also reduces damage to healthy tissue

IGRT augments radiotherapy with imaging to increase the accuracy and precision of target localization, thereby reducing the amount of healthy tissue in the treatment field. Image-guided radiation therapy (IGRT) is the process of frequent two and three-dimensional imaging, during a course of radiation treatment, used to direct radiation therapy utilizing the imaging coordinates of the actual radiation treatment plan. ... Image-guided radiation therapy (IGRT) is the process of frequent two and three-dimensional imaging, during a course of radiation treatment, used to direct radiation therapy utilizing the imaging coordinates of the actual radiation treatment plan. ...

References

See also Gamma knife. In medicine, Leksell Gamma Knife is a neurosurgical device used to treat brain tumors. ...

General References

• Radiotherapy physics in practice, edited by JR Williams and DI Thwaites, Oxford University Press UK (2nd edition 2000), ISBN 0-19-262878-X