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42-546: [REDACTED] Look up gantry in Wiktionary, the free dictionary. A gantry is an overhead bridge-like structure supporting equipment such as a crane, signals, or cameras. Devices and structures [ edit ] Gantry (medical) , cylindrical scanner assembly used for medical 3D-imaging or treatment Gantry (transport) , an overhead assembly on which highway signs or railway signals are posted Gantry (rocketry) ,

84-428: A linear accelerator is most commonly used to produce X-rays of such energy. X-ray emission is more forward-directed at megavoltage energies and more laterally-directed at kilovoltage energies. Consequently, kilovoltage X-rays tend to be produced using a reflection-type target, in which the radiation is emitted back from the target's surface, while megavoltage X-rays tend to be produced with a transmission target in which

126-493: A 100 kVp beam is produced by a 100 kV voltage applied to an X-ray tube and will have a maximum photon energy of 100 keV. However, the beam's spectrum can be affected by other factors as well, such as the voltage waveform and external X-ray filtration . These factors are reflected in the beam's half-value layer (HVL), measured in-air under conditions of "good geometry". A typical superficial X-ray energy might be 100 kVp per 3 mmAl – "100 kilovolts applied to

168-400: A depth of approximately 5 cm. A small number of centers operate experimental and pilot programs employing beams of heavier particles, particularly protons , owing to the rapid decrease in absorbed dose beneath the depth of the target. Teletherapy is the most common form of radiotherapy ( radiation therapy ). The patient sits or lies on a couch and an external source of ionizing radiation

210-430: A high atomic number material with electrons. If the target is removed (and the beam current decreased). a high energy electron beam is obtained. Electron beams are useful for treating superficial lesions, because the maximum dose deposition occurs near the surface and thereafter decreases rapidly with depth, sparing underlying tissue. Electron beams usually have nominal energies in the range of 4–20 MeV, corresponding to

252-404: A high-energy collimated beam of ionizing radiation , from a source outside the body, to target and kill cancer cells . A radiotherapy beam is composed of particles which travel in a consistent direction; each radiotherapy beam consists of one type of particle intended for use in treatment, though most beams contain some contamination by other particle types. Radiotherapy beams are classified by

294-412: A linac for medical radiotherapy was in 1953. 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

336-410: A linac may be modified or collimated by a variety of means. Thus, conventional, conformal, intensity-modulated, tomographic , and stereotactic radiotherapy are all provided using specially-modified linear accelerators. Cobalt units use radiation from cobalt-60, which emits two gamma rays at energies of 1.17 and 1.33 MeV, a dichromatic beam with an average energy of 1.25 MeV. The role of

378-443: A patient. A klystron in the drive stand behind the gantry supplies radio frequency energy to the linac. The linac accelerates a pencil size beam of electrons horizontally. After leaving the linac, the electrons are deflected and focussed downward by magnets, causing the electrons to strike tungsten target. The target stops the electrons, and the sudden deceleration results in bremsstrahlung radiation of X-rays . The photo below

420-411: A radiation source around a patient. A linear accelerator (linac) is built into the top part of the gantry in the photo at the right. The rectangular screen on the right side of the gantry is a cone beam x-ray detector, which is used to help position a patient prior to treatment. The gantry is supported by a drive stand, which rotates the gantry on a fixed horizontal axis as the linac revolves around

462-423: A reduction in the effect of patient motion on the delivery of the treatment. This makes FFF an area of particular interest in stereotactic treatments. For instance, in treatment of breast cancer , the reduced treatment time may reduce patient movement and breast treatments where there is the potential to reduce breathing motion. Image-guided radiation therapy (IGRT) augments radiotherapy with imaging to increase

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504-531: A support framework Places [ edit ] Gantry Plaza State Park , in New York City Arts, entertainment, and media [ edit ] Elmer Gantry , a 1927 novel by Sinclair Lewis Elmer Gantry (film) , a 1960 film based on the novel Gantry (musical) , a 1970 musical by Peter Bellwood, Fred Tobias, and Stanley Lebowsky, based on the novel See also [ edit ] Gentry (disambiguation) Topics referred to by

546-456: A target made of a material with high atomic number, such as tungsten . The target acts as a sort of transducer , converting part of the electrons' kinetic energy into energetic photons . Kilovoltage X-rays are typically produced using an X-ray tube , in which electrons travel through a vacuum from a hot cathode to a cold anode , which also acts as the target. However, it is impractical to produce megavoltage X-rays using this method; instead,

588-458: A treatment range of approximately 1–5 cm (in water-equivalent tissue). Energies above 18 MeV are rarely used. Although the X-ray target is removed in electron mode, the beam must be fanned out by sets of thin scattering foils in order to achieve flat and symmetric dose profiles in the treated tissue. Many linear accelerators can produce both electrons and x-rays. Hadron therapy involves

630-477: Is an advanced radiotherapy technique used to minimize the amount of normal tissue being irradiated in the treatment field. In some systems, this intensity modulation is achieved by moving the leaves in the MLC during the course of treatment, thereby delivering a radiation field with a non-uniform (i.e., modulated) intensity. Using IMRT, radiation oncologists are able to split the radiation beam into many beamlets and vary

672-486: Is desirable to maximize "skin-sparing" (since the relative dose to the skin is lower for such high-energy beams). Medically useful photon beams can also be derived from a radioactive source such as iridium-192 , caesium-137 , or cobalt-60 . ( Radium-226 has also been used as such a source in the past, though has been replaced in this capacity by less harmful radioisotopes.) Such photon beams, derived from radioactive decay , are approximately monochromatic , in contrast to

714-401: Is different from Wikidata All article disambiguation pages All disambiguation pages Gantry (medical) The gantry of a computed tomography scanner (CT) is a ring or cylinder, into which a patient is placed. The x-ray tube and x-ray detector spin rapidly in the gantry, as the patient is moved in and out of the gantry. The CT scanner produces 3-dimensional x-ray images of

756-405: Is of a different gantry rotated to about 45°. The apparatus attached to the left side of the gantry is a cone beam x-ray source, with the x-ray detector on the right side. Prior to treatment, the cone beam x-ray system is used to align the patient's tumor with the radiation. External beam radiotherapy External beam radiation therapy ( EBRT ) is a form of radiotherapy that utilizes

798-437: Is pointed at a particular part of the body. In contrast to brachytherapy (sealed source radiotherapy) and unsealed source radiotherapy , in which the radiation source is inside the body, external beam radiotherapy directs the radiation at the tumor from outside the body. Conventionally, the energy of diagnostic and therapeutic gamma- and X-rays is on the order of kiloelectronvolts (keV) or megaelectronvolts (MeV), and

840-472: The X-ray tube with a measured half-value layer of 3 millimeters of aluminum ". The half-value layer for orthovoltage beams is more typically measured using copper; a typical orthovoltage energy is 250 kVp per 2 mmCu. For X-rays in the MeV range, an actual voltage of the same magnitude is not used in production of the beam. A 6 MV beam contains photons of no more than 1 MeV, rather than 6 MeV;

882-466: The X-rays are emitted on the side opposite that of electron incidence. Reflection type targets exhibit the heel effect and can use a rotating anode to aid in heat dissipation. Compton scattering is the dominant interaction between a megavoltage beam and the patient, while the photoelectric effect dominates at keV energies. Additionally, Compton scattering is much less dependent on atomic number than

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924-504: The accuracy and precision of target localization, thereby reducing the amount of healthy tissue in the treatment field. To allow patients to benefit from sophisticated treatment techniques as IMRT or hadron therapy, patient alignment accuracies with an error margin of at most 0.5 mm are desirable. Therefore, methods such as stereoscopic digital kilovoltage imaging-based patient position verification (PPVS), and alignment estimation based on in-situ cone-beam computed tomography (CT), enrich

966-426: The centre of the beam compared to the edges. To offset this central peak, a flattening filter is used. A flattening filter is cone-shaped so as to compensate for the forward bias in the momentum of incident electrons (and is typically made from a metal such as tungsten); after an X-ray beam passes through the flattening filter, it has a more uniform profile. This simplifies treatment planning, though significantly reduces

1008-469: The cobalt unit has largely been replaced by the linear accelerator, which can generate higher energy radiation. Nonetheless, cobalt treatment still retains some applications, such as the Gamma Knife , since the machinery is relatively reliable and simple to maintain compared to the modern linear accelerator. Bremsstrahlung X-rays are produced by bombarding energetic cathode rays ( electrons ) onto

1050-421: The continuous bremsstrahlung spectrum from a linac. These decays include the emission of gamma rays , whose energy is isotope -specific and ranges between 300 keV and 1.5 MeV. Superficial radiation therapy machines produce low energy x-rays in the same energy range as diagnostic x-ray machines, 20–150 keV, to treat skin conditions. Orthovoltage X-ray machines produce higher energy x-rays in

1092-420: The energy of such a beam is instead generally characterized by measuring the ratio of the beam's intensity at varying depths in a medium. Kilovoltage beams do not exhibit a build-up effect and thus deposit their maximum dose at the surface, i.e. d max  = 0 or D 0  = 100%. Conversely, megavoltage beams do exhibit the buildup effect deposit; they deposit their maximum dose at some depth below

1134-417: The energy of therapeutic electrons is on the order of megaelectronvolts. The beam is made up of a spectrum of energies: the maximum energy is approximately equal to the beam's maximum electric potential within a linear accelerator times the electron charge . For instance, a 1 megavolt beam will produce photons with a maximum energy around 1 MeV. In practice, the mean X-ray energy is about one-third of

1176-411: The former and 1 MeV for the latter), for therapeutic X-ray beams. Some examples of X-ray energies used in medicine are: Megavoltage X-rays are by far most common in radiotherapy for the treatment of a wide range of cancers. Superficial and orthovoltage X-rays have application for the treatment of cancers at or close to the skin surface. Typically, higher-energy megavoltage X-rays are chosen when it

1218-412: The frame which encloses and services a rocket at its launch pad Gantry crane , a crane having a hoist fitted in a trolley for parallel movement Rubber tyred gantry crane , a mobile gantry crane used in intermodal operations Gantry tower or anchor portal, a structure commonly found in electrical substation or transmission line Scaffolding , occasionally referred to as a gantry when used as

1260-428: The intensity of each beamlet, and doctors are often able to further limit the amount of radiation received by healthy tissue near the tumor. Doctors have found that this sometimes allows them to safely give a higher dose of radiation to the tumor, potentially increasing the chance of successful treatment. Volumetric modulated arc therapy (VMAT) is an extension of IMRT characterized by a linear accelerator rotating around

1302-482: The intensity of the beam. With greater computing power and more efficient treatment planning algorithms, the need for simpler treatment planning techniques – such as "forward planning", in which the planner directly instructs the linac on how to deliver the prescribed treatment – is reduced. This has led to increased interest in flattening filter free (FFF) treatments. FFF treatments have been found to have an increased maximum dose rate, allowing reduced treatment times and

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1344-507: The maximum energy. Beam quality and hardness may be improved by X-ray filters , which improves the homogeneity of the X-ray spectrum. Medically useful X-rays are produced when electrons are accelerated to energies at which either the photoelectric effect predominates (for diagnostic use, since the photoelectric effect offers comparatively excellent contrast with effective atomic number Z ) or Compton scattering and pair production predominate (at energies above approximately 200 keV for

1386-452: The other two dimensions. Each leaf in the MLC is aligned parallel to the radiation field and can be moved independently to block part of the field, adapting it to the shape of the tumor (by adjusting the position of the leaves), thus minimizing the amount of healthy tissue subject to radiation exposure. On older linacs without MLCs, this must be accomplished manually using several hand-crafted blocks. Intensity modulated radiation therapy (IMRT)

1428-523: The particle they are intended to deliver, such as photons (as x-rays or gamma rays ), electrons , and heavy ions ; x-rays and electron beams are by far the most widely used sources for external beam radiotherapy. Orthovoltage ("superficial") X-rays are used for treating skin cancer and superficial structures. Megavoltage X-rays are used to treat deep-seated tumors (e.g. bladder, bowel, prostate, lung, or brain), whereas megavoltage electron beams are typically used to treat superficial lesions extending to

1470-474: The patient. An MRI gantry remains fixed, and contains cryogenically cooled superconducting electromagnets and radio transmitters that flip protons in hydrogen atoms in the human body via proton nuclear magnetic resonance . The machine then listens and processes the signals given off by the hydrogen atoms as the protons flip back in order to produce a 3D image of the interior of the patient's body. The gantry of an external beam radiotherapy machine moves

1512-414: The patient. This means that rather than radiation entering the patient at only a small number of fixed angles, it can enter at many angles. This can be beneficial for some treatment sites in which the target volume is surrounded by a number, allowing directed treatment without exposing nearby organs to heightened radiation levels. The intensity of the X-rays produced in a megavoltage linac is much higher in

1554-444: The photoelectric effect; while kilovoltage beams enhance the distinction between muscle and bone in medical imaging , megavoltage beams suppress that distinction to the advantage of teletherapy. Pair production and photoneutron production increase at higher energies, only becoming significant at energies on the order of 1 MeV. X-ray energy in the keV range is described by the electrical voltage used to produce it. For instance,

1596-437: The radiation field as the linac gantry rotates, and block the field as necessary according to the gantry position. This technology allows radiotherapy treatment planners great flexibility in shielding organs-at-risk (OARSs), while ensuring that the prescribed dose is delivered to the target organs. A typical multi-leaf collimator consists of two sets of 40 to 160 leaves, each around 5–10 mm thick and several centimetres long in

1638-539: The range 200–500 keV. Radiation from orthovoltage x-ray machines has been called "deep" due to its greater penetrating ability, allowing it to treat tumors at depths unreachable by lower-energy "superficial" radiation. Orthovoltage units have essentially the same design as diagnostic X-ray machines and are generally limited to photon energies less than 600 keV. X-rays with energies on the order of 1 MeV are generated in Linear accelerators ("linacs"). The first use of

1680-409: The same term [REDACTED] This disambiguation page lists articles associated with the title Gantry . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Gantry&oldid=1086425214 " Category : Disambiguation pages Hidden categories: Short description

1722-422: The surface, i.e. d max  > 0. The depth of dose maximum is governed by the range of the electrons liberated upstream during Compton scattering. At depths beyond d max , the dose profile of all X-ray beams decreases roughly exponentially with depth. Though actual values of d max are influenced by various factors, the following are representative benchmark values. X-rays are generated by bombarding

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1764-527: The therapeutic use of protons , neutrons , and heavier ions (fully ionized atomic nuclei). Of these, proton therapy is by far the most common, though still rare compared to other forms of external beam radiotherapy, since it requires large and expensive equipment. The gantry (the part that rotates around the patient) is a multi-story structure, and a proton therapy system can cost (as of 2009) up to US$ 150 million. Modern linear accelerators are equipped with multileaf collimators (MLCs), which can move within

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