|
Megavoltage
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. Megavoltage x-rays are preferred for 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 than ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
External Beam Radiotherapy
External beam radiotherapy (EBRT) is the most common form of radiotherapy (radiation therapy). 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 (sealed source radiotherapy) 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 (e.g. bladder, bowel, prostate, lung, or brain), whereas megavoltage electron beams are typically used to treat superficial lesions extending to a depth of approximately 5 cm (increasing beam energy corresponds to greater penetration). 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 pi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
External Beam Radiotherapy
External beam radiotherapy (EBRT) is the most common form of radiotherapy (radiation therapy). 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 (sealed source radiotherapy) 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 (e.g. bladder, bowel, prostate, lung, or brain), whereas megavoltage electron beams are typically used to treat superficial lesions extending to a depth of approximately 5 cm (increasing beam energy corresponds to greater penetration). 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 pi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 cover the upper limit of energies used for diagnostic radiography, and are used in external beam radiotherapy to treat cancer and tumors. They penetrate tissue to a useful depth of about 4–6 cm. This makes them useful for treating skin, superficial tissues, and ribs, but not for deeper structures such as lungs or pelvic organs. The relatively low energy of orthovoltage X-rays causes them to interact with matter via different physical mechanisms compared to higher energy megavoltage X-rays or radionuclide γ-rays, increasing their relative biological effectiveness. History The energy and penetrating ability of the X-rays produced by an X-ray tube increases with the voltage on the tube. External beam radiotherapy began around ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 cover the upper limit of energies used for diagnostic radiography, and are used in external beam radiotherapy to treat cancer and tumors. They penetrate tissue to a useful depth of about 4–6 cm. This makes them useful for treating skin, superficial tissues, and ribs, but not for deeper structures such as lungs or pelvic organs. The relatively low energy of orthovoltage X-rays causes them to interact with matter via different physical mechanisms compared to higher energy megavoltage X-rays or radionuclide γ-rays, increasing their relative biological effectiveness. History The energy and penetrating ability of the X-rays produced by an X-ray tube increases with the voltage on the tube. External beam radiotherapy began around ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cobalt Therapy
Cobalt therapy is the medical use of gamma rays from the radioisotope cobalt-60 to treat conditions such as cancer. Beginning in the 1950s, cobalt-60 was widely used in external beam radiotherapy (teletherapy) machines, which produced a beam of gamma rays which was directed into the patient's body to kill tumor tissue. Because these "cobalt machines" were expensive and required specialist support, they were often housed in ''cobalt units''. Cobalt therapy was a revolutionary advance in radiotherapy in the post-World War II period but is now being replaced by other technologies such as linear accelerators. History Before the development of medical linear accelerators in the 1970s, the only artificial radiation source used for teletherapy was the x-ray tube. Researchers found ordinary x-ray tubes, which used voltages of 50-150 keV, could treat superficial tumors, but did not have the energy to reach tumors deep in the body. To have the penetrating ability to reach deep- ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 and medical oncology, involved in the treatment of cancer. Radiation can be given as a curative modality, either alone or in combination with surgery and/or chemotherapy. It may also be used palliatively, to relieve symptoms in patients with incurable cancers. A radiation oncologist may also use radiation to treat some benign diseases, including benign tumors. In some countries (not the United States), radiotherapy and chemotherapy are controlled by a single oncologist who is a "clinical oncologist". Radiation oncologists work closely with other physicians such as surgical oncologists, interventional radiologists, internal medicine subspecialists, and medical oncologists, as well as medical physicists and technicians as part of the multi-di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IMRT
Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radiation therapy may be curative in a number of types of cancer if they are localized to one area of the body. It may also be used as part of adjuvant therapy, to prevent tumor recurrence after surgery to remove a primary malignant tumor (for example, early stages of breast cancer). Radiation therapy is synergistic with chemotherapy, and has been used before, during, and after chemotherapy in susceptible cancers. The subspecialty of oncology concerned with radiotherapy is called radiation oncology. A physician who practices in this subspecialty is a radiation oncologist. Radiation therapy is commonly applied to the cancerous tumor because of its ability to control cell growth. Ionizing radiation works by damaging the DNA of cancerous tissue l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Betatron
A betatron is a type of cyclic particle accelerator. It is essentially a transformer with a torus-shaped vacuum tube as its secondary coil. An alternating current in the primary coils accelerates electrons in the vacuum around a circular path. The betatron was the first machine capable of producing electron beams at energies higher than could be achieved with a simple electron gun, and the first circular accelerator in which particles orbited at a constant radius. The concept of the betatron had been proposed as early as 1922 by Joseph Slepian. Through the 1920s and 30s a number of theoretical problems related to the device were considered by scientists including Rolf Wideroe, Ernest Walton, and Max Steenbeck. The first working betatron was constructed by Donald Kerst at the University of Illinois Urbana-Champaign in 1940. History After the discovery in the 1800s of Faraday's law of induction, which showed that an electromotive force could be generated by a changing magneti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 current (DC) electricity at low current levels. It was invented by American physicist Robert J. Van de Graaff in 1929. The potential difference achieved by modern Van de Graaff generators can be as much as 5 megavolts. A tabletop version can produce on the order of 100 kV and can store enough energy to produce visible electric sparks. Small Van de Graaff machines are produced for entertainment, and for physics education to teach electrostatics; larger ones are displayed in some science museums. The Van de Graaff generator was originally developed as a particle accelerator for physics research, as its high potential can be used to accelerate subatomic particles to great speeds in an evacuated tube. It was the most powerful type of accelera ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 beamline. The principles for such machines were proposed by Gustav Ising in 1924, while the first machine that worked was constructed by Rolf Widerøe in 1928 at the RWTH Aachen University. Linacs have many applications: they generate X-rays and high energy electrons for medicinal purposes in radiation therapy, serve as particle injectors for higher-energy accelerators, and are used directly to achieve the highest kinetic energy for light particles (electrons and positrons) for particle physics. The design of a linac depends on the type of particle that is being accelerated: electrons, protons or ions. Linacs range in size from a cathode ray tube (which is a type of linac) to the linac at the SLAC National Accelerator Laboratory in Menlo Park ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 absorbed dose, amount of absorbed energy. The RBE is an empirical value that varies depending on the type of ionizing radiation, the energies involved, the biological effects being considered such as cell death, and the oxygen tension of the tissues or so-called oxygen effect. Application The absorbed dose can be a poor indicator of the biological effect of radiation, as the biological effect can depend on many other factors, including the type of radiation, energy, and type of tissue. The relative biological effectiveness can help give a better measure of the biological effect of radiation. The relative biological effectiveness for radiation of type ''R'' on a tissue is defined as the ratio :RBE= \frac where ''D''''X'' is a reference absorbed dose of radiation of a standard type ''X'', ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage is named ''volt''. The voltage between points can be caused by the build-up of electric charge (e.g., a capacitor), and from an electromotive force (e.g., electromagnetic induction in generator, inductors, and transformers). On a macroscopic scale, a potential difference can be caused by electrochemical processes (e.g., cells and batteries), the pressure-induced piezoelectric effect, and the thermoelectric effect. A voltmeter can be used to measure the voltage between two points in a system. Often a common reference potential such as the ground of the system is used as one of the points. A voltage can represent either a source ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
