External beam radiotherapy

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External file radiation ( EBRT ) or teleterapy is the most common form of radiotherapy (radiation therapy). The patient sits down or lies on the couch and an external source of ionizing radiation refers to a particular part of the body. Unlike brachytherapy (sealed source radiotherapy) and sealed source radiotherapy, where the source of radiation in the body, external radiotherapy directs radiation to the tumor from outside the body. Orthovoltage ("superficial") X-rays are used to treat skin cancers and superficial structures. Megavoltage ("in") X-rays are used to treat deep tumors (eg bladder, intestine, prostate, lung, or brain).

X-rays and electron beams are the most widely used source for external beam radiotherapy. A small number of centers operate experimental and pilot programs using heavier particle beams, especially protons.

Video External beam radiotherapy

Sinar-X dan sinar gamma

Conventionally, gamma ray energy and diagnostic and therapeutic X-rays are expressed in kilovolts or megavolts (kV or MV), while therapeutic electron energy is expressed in terms of megaelectronvolts (MeV). In the first case, this voltage is the maximum electrical potential used by the linear accelerator to produce the photon beam. This ray consists of the energy spectrum: the maximum energy is approximately equal to the maximum electrical potential of the electron charge times. Thus a 1 MV beam will produce no more than 1 MeV of photons. Energy the average X-ray is only about 1/3 of the maximum energy. The quality and hardness of the beams can be enhanced with X-ray filters, which increase the homogeneity of the X-ray spectrum.

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

• superficial X-rays - 35 to 60 keV
• X-ray diagnostics - 20 to 150 keV
• orthovoltage X-ray - 200 to 500 keV
• X-rays supervoltage - 500 to 1000 keV
• megavoltage X-rays - 1 to 25 MeV

Megavoltage X-rays are the most common in radiotherapy for the treatment of various cancers. Superficial X rays and orthovoltage have applications for the treatment of cancer at or near the surface of the skin.

Medically useful photon bubbles may also come from radioactive sources such as iridium-192, cesium-137 or radium-226 (which are no longer used clinically), or cobalt-60. Such photon balloons, derived from radioactive decay, are more or less monochromatic and are named gamma rays. The usual energy range is between 300 keV to 1.5 MeV, and isotope specific.

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

Superficial radiation therapy (SRT) produces low energy x-rays in the same energy range as the diagnostic x-ray machine, 20-150 kV, to treat skin conditions.

Orthovoltage X-ray machine, which produces a higher x-ray energy in the 200-500 kV range. This radiation is called "deep" because it can treat tumors at depths where the "superficial" energy radiation lower (above) does not match. The orthovoltage unit basically has the same design as a diagnostic X-ray machine. These machines are generally limited to less than 600 kV.

Linear accelerator ("linacs") that generates megavoltage X-rays. The first use of linac for medical radiotherapy was in 1953 (see also Radiation therapy). The commercially available medical line produces X-rays and electrons with an energy range from 4 MeV to about 25 MeV. The X-rays themselves are produced by rapid decelerations of electrons in the target material, typically tungsten alloys, which produce the X-ray spectra through bremsstrahlung radiation. The shape and intensity of light produced by linacs can be modified or colonized in various ways. Thus, conventional, conformal, intensity-modulated, tomographic and stereotactic radiotherapy are all produced by specially modified linear accelerators.

Cobalt unit using radiation from cobalt-60 radioisotope produces stable and chromatic beams of 1.17 and 1.33 MeV, producing an average beam energy of 1.25 MeV. The role of the cobalt unit has been replaced by a linear accelerator, which can produce higher energy radiation. Cobalt treatment still has a useful role to play in certain applications (eg Gamma Knives) and is still widely used throughout the world, because the engine is relatively reliable and easy to maintain compared to modern linear accelerators.

Maps External beam radiotherapy

Electrons

X-rays are produced by bombarding large amounts of atomic material with electrons. If the target is removed (and the file flow decreases), high-energy electron beam is obtained. Electron bundles are useful for treating superficial lesions because the maximum dose deposition occurs near the surface. The dose then decreases rapidly with depth, sparing the tissue underneath. Electron bundles usually have nominal energy in the range of 4-20 MeV. Depending on this energy it translates into a treatment range of about 1-5 cm (in a network equivalent to water). Energy above 18 MeV is very rarely used. Although the target X-ray is removed in electron mode, the rays should spread with a thin scattering foil set to achieve a flat and symmetrical dose profile in the treated tissue.

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Hadron therapy

Hadron therapy involves therapeutic use of protons, neutrons, and heavier ions (full ionized ion nuclei). Of these, proton therapy is by far the most common, although it is still very rare compared to other forms of external beam radiotherapy.

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Multi-leaf collimator

Modern linear accelerators are equipped with multi-leaf collimators (MLCs) that can move into the field of radiation and block some of it. A typical multi-leaf collimator consists of two sets of 40 to 80 leaves, each about 5 mm to 10 mm and several centimeters in the other two dimensions. The new MLC now has up to 160 leaves. Each leaf in MLC is parallel to the radiation plane and can be moved independently to block part of the field. This allows dosimetris to match the radiation field to the shape of the tumor (by adjusting the leaf position), thus minimizing the amount of healthy tissue exposed to radiation. On machines without MLC this must be completed using some handmade blocks.

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Intensity modulated radiation therapy

Intensified modulated radiation therapy (IMRT) is an advanced radiotherapy technique used to minimize the amount of normal tissue irradiated in the treatment field. In some systems this intensity modulation is achieved by removing the leaves in MLC during treatment, thus providing a radiation field with a non-uniform intensity (ie modulated). With IMRT, radiation oncologists can break the radiation beam into many "small blocks". This allows the radiation oncologist to vary the intensity of each beamlet. With IMRT, doctors can often limit further the amount of radiation received by healthy tissue near the tumor. Doctors have found this sometimes allows them to safely deliver higher radiation doses to the tumor, potentially increasing the chances of healing.

Volumetric Modulation Arc Therapy

Volumetric Modulated Arc Therapy (VMAT) is an IMRT extension in which in addition to MLC motion, a linear accelerator will move around the patient during treatment. This means that rather than the radiation that enters the patient through only a small number of fixed angles, it can enter through many angles. This can be useful for some treatment sites where the target volume is surrounded by a number of organs that must avoid radiation dose.

Flattening Filter Free

The intensity of the X-rays produced in LINAC megavoltage is much higher in the center of the ray than the edge. To counter this, flat filters are used. A uniform filter is a metal cone, once an X-ray beam passes through a flat filter it will have a more uniform profile. This makes planning maintenance simpler but also reduces the intensity of the rays significantly. With faster computers and modern maintenance planning methods, the need for simpler maintenance planning will be reduced. This has led to increased interest in filter free filtering treatment (FFF). The advantage of the FFF treatment is the increase in the maximum dose rate, possibly allowing a reduction in treatment time. This makes the FFF an area of ​​special interest in stereotactic care. , where reduced care time can reduce patient movement, and breast care, where there is potential to reduce breathing movements.

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Radiation therapy with image guidance

Radiation therapy with image guidance (IGRT) adds radiotherapy with imaging to improve accuracy and precision of localization targets, thereby reducing the number of healthy tissue in the treatment field. The more advanced the maintenance technique becomes in terms of dose deposition accuracy, the higher being the requirement for IGRT. To enable patients to benefit from advanced treatment techniques such as IMRT or Hadron Therapy, a patient's alignment accuracy of 0.5 mm and less is desirable. Therefore, new methods such as digital stereoscopic kilovoltage imaging based on patient position verification (PPVS) for alignment estimation based on CT Cone-Beam in-situ enrich the range of modern IGRT approaches.

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See also

• Brachytherapy
• Cyberknife
• Gamma Knife, a kind of radiosurgery
• Intraoperative electron radiation therapy
• Intraoperative radiation therapy
• Neutron capture therapy from cancer
• Radiation therapy
• Tomoterapi

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References

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General reference

• Radiotherapy physics in practice , edited by JR Williams and DI Thwaites, Oxford University Press UK (2nd edition 2000), ISBNÃ, 0-19-262878-X
• Linear Particle Accelerator (Linac) Animation by Ionactive
  • http://www.myradiotherapy.com
• Superficial radiation therapy
• National Institute of Radiology (Japan)

Source of the article : Wikipedia