 | This article needs additional citations for verification .(August 2010) |
A beam spoiler is a piece of material, placed into the path of the photon beam in radiotherapy. The purpose of the spoiler is to reduce the depth of the maximum radiation dosage. [1]
The beam spoiler is composed of a sheet of material which has a low atomic number, [2] typically lucite, the thickness of which is varied according to the beam energy and the distance by which the radiation dose must be shifted. [1]
As the primary photon beam passes through the plate, secondary electrons are generated. The beam exiting the spoiler is a combination of the spoiler-attenuated photons and the spoiler-generated electrons. The electron component alters the depth dose in the buildup region in a way that depends on the photon beam energy, the field size, and the distance of the spoiler from the treatment surface.
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 145 eV to 124 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it on November 8, 1895. He named it X-radiation to signify an unknown type of radiation. Spellings of X-ray(s) in English include the variants x-ray(s), xray(s), and X ray(s). The most familiar use of X-rays is checking for fractures (broken bones), but X-rays are also used in other ways. For example, chest X-rays can spot pneumonia. Mammograms use X-rays to look for breast cancer.
Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical radiography and industrial radiography. Similar techniques are used in airport security. To create an image in conventional radiography, a beam of X-rays is produced by an X-ray generator and is projected toward the object. A certain amount of the X-rays or other radiation is absorbed by the object, dependent on the object's density and structural composition. The X-rays that pass through the object are captured behind the object by a detector. The generation of flat two dimensional images by this technique is called projectional radiography. In computed tomography an X-ray source and its associated detectors rotate around the subject which itself moves through the conical X-ray beam produced. Any given point within the subject is crossed from many directions by many different beams at different times. Information regarding attenuation of these beams is collated and subjected to computation to generate two dimensional images in three planes which can be further processed to produce a three dimensional image.
Ionizing radiation, including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel up to 99% of the speed of light, and the electromagnetic waves are on the high-energy portion of the electromagnetic spectrum.
External beam radiotherapy (EBRT) is the most common form of radiotherapy. The patient sits or lies on a couch and an external source of ionizing radiation is pointed at a particular part of the body. In contrast to brachytherapy and unsealed source radiotherapy, in which the radiation source is inside the body, external beam radiotherapy directs the radiation at the tumour from outside the body. Orthovoltage ("superficial") X-rays are used for treating skin cancer and superficial structures. Megavoltage X-rays are used to treat deep-seated tumours, whereas megavoltage electron beams are typically used to treat superficial lesions extending to a depth of approximately 5 cm. X-rays and electron beams are by far the most widely used sources for external beam radiotherapy. A small number of centers operate experimental and pilot programs employing beams of heavier particles, particularly protons, owing to the rapid dropoff in absorbed dose beneath the depth of the target.
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. They are used in medicine in external beam radiotherapy to treat neoplasms, cancer and tumors. Beams with the 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. Lower energy x-rays, called orthovoltage X-rays, are used to treat cancers closer to the surface.
A synchrotron light source is a source of electromagnetic radiation (EM) usually produced by a storage ring, for scientific and technical purposes. First observed in synchrotrons, synchrotron light is now produced by storage rings and other specialized particle accelerators, typically accelerating electrons. Once the high-energy electron beam has been generated, it is directed into auxiliary components such as bending magnets and insertion devices in storage rings and free electron lasers. These supply the strong magnetic fields perpendicular to the beam which are needed to convert high energy electrons into photons.
In medicine, proton therapy, or proton radiotherapy, is a type of particle therapy that uses a beam of protons to irradiate diseased tissue, most often to treat cancer. The chief advantage of proton therapy over other types of external beam radiotherapy is that the dose of protons is deposited over a narrow range of depth; hence in minimal entry, exit, or scattered radiation dose to healthy nearby tissues.
Radiosurgery is surgery using radiation, that is, the destruction of precisely selected areas of tissue using ionizing radiation rather than excision with a blade. Like other forms of radiation therapy, it is usually used to treat cancer. Radiosurgery was originally defined by the Swedish neurosurgeon Lars Leksell as "a single high dose fraction of radiation, stereotactically directed to an intracranial region of interest".
A monitor unit (MU) is a measure of machine output from a clinical accelerator for radiation therapy such as a linear accelerator or an orthovoltage unit. Monitor units are measured by monitor chambers, which are ionization chambers that measure the dose delivered by a beam and are built into the treatment head of radiotherapy linear accelerators.
A radiation burn is a damage to the skin or other biological tissue and organs as an effect of radiation. The radiation types of greatest concern are thermal radiation, radio frequency energy, ultraviolet light and ionizing radiation.
Extreme ultraviolet radiation or high-energy ultraviolet radiation is electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths shorter that the hydrogen Lyman-alpha line from 121 nm down to the X-Ray band of 10 nm, and therefore having photons with energies from 10.26 eV up to 124.24 eV. EUV is naturally generated by the solar corona and artificially by plasma, high harmonic generation sources and synchrotron light sources. Since UVC extends to 100 nm, there is some overlap in the terms.
Fast neutron therapy utilizes high energy neutrons typically between 50 and 70 MeV to treat cancer. Most fast neutron therapy beams are produced by reactors, cyclotrons (d+Be) and linear accelerators. Neutron therapy is currently available in Germany, Russia, South Africa and the United States. In the United States, one treatment center is operational, in Seattle, Washington. The Seattle center uses a cyclotron which produces a proton beam impinging upon a beryllium target.
Electron therapy or electron beam therapy (EBT) is a kind of external beam radiotherapy where electrons are directed to a tumor site for medical treatment of cancer.
Intraoperative radiation therapy (IORT) is radiation therapy that is administered during surgery directly in the operating room.
Particle therapy is a form of external beam radiotherapy using beams of energetic neutrons, protons, or other heavier positive ions for cancer treatment. The most common type of particle therapy as of August 2021 is proton therapy.
In radiotherapy, a percentage depth dose curve (PDD) relates the absorbed dose deposited by a radiation beam into a medium as it varies with depth along the axis of the beam. The dose values are divided by the maximum dose, referred to as dmax, yielding a plot in terms of percentage of the maximum dose. Dose measurements are generally made in water or "water equivalent" plastic with an ionization chamber, since water is very similar to human tissue with regard to radiation scattering and absorption.
Tissue-to-air ratio (TAR) is a term used in radiotherapy treatment planning to help calculate absorbed dose to water in conditions other than those directly measured.
A gamma ray, also known as gamma radiation (symbol γ or ), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically shorter than those of X-rays. With frequencies above 30 exahertz (3×1019 Hz), it imparts the highest photon energy. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation gamma rays based on their relatively strong penetration of matter; in 1900 he had already named two less penetrating types of decay radiation (discovered by Henri Becquerel) alpha rays and beta rays in ascending order of penetrating power.
Cherenkov radiation is electromagnetic radiation emitted when a charged particle passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. A classic example of Cherenkov radiation is the characteristic blue glow of an underwater nuclear reactor. Its cause is similar to the cause of a sonic boom, the sharp sound heard when faster-than-sound movement occurs. The phenomenon is named after Soviet physicist Pavel Cherenkov.
Auger therapy is a form of radiation therapy for the treatment of cancer which relies on low-energy electrons to damage cancer cells, rather than the high-energy radiation used in traditional radiation therapy. Similar to other forms of radiation therapy, Auger therapy relies on radiation-induced damage to cancer cells to arrest cell division, stop tumor growth and metastasis and kill cancerous cells. It differs from other types of radiation therapy in that electrons emitted via the Auger effect are released with low kinetic energy. In contrast to traditional α- and β-particle emitters, Auger electron emitters exhibit low cellular toxicity during transit in blood or bone marrow.
 | This optics-related article is a stub. You can help Wikipedia by expanding it. |
 | This article related to medical equipment is a stub. You can help Wikipedia by expanding it. |