Editing Linear particle accelerator (section)

==Advantages==
[[Image:Stanford SCA July 1995 16a.jpg|thumb|right|250px|The [[Stanford University]] superconducting linear accelerator, housed on campus below the Hansen Labs until 2007. This facility is separate from [[Stanford Linear Accelerator Center|SLAC]]]]
[[File:Linear Accelerator.jpg|thumb|right|250px|Steel casting undergoing x-ray using the linear accelerator at [[Goodwin Steel Castings Ltd]]]]

The linear accelerator could produce higher particle energies than the previous [[electrostatic particle accelerator]]s (the [[Cockcroft–Walton accelerator]] and [[Van de Graaff generator]]) that were in use when it was invented. In these machines, the particles were only accelerated once by the applied voltage, so the particle energy in [[electron volts]] was equal to the accelerating voltage on the machine, which was limited to a few million volts by insulation breakdown.  In the linac, the particles are accelerated multiple times by the applied voltage, so the particle energy is not limited by the accelerating voltage.

High power linacs are also being developed for production of electrons at relativistic speeds, required since fast electrons traveling in an arc will lose energy through [[synchrotron radiation]]; this limits the maximum power that can be imparted to electrons in a synchrotron of given size. Linacs are also capable of prodigious output, producing a nearly continuous stream of particles, whereas a synchrotron will only periodically raise the particles to sufficient energy to merit a "shot" at the target. (The burst can be held or stored in the ring at energy to give the experimental electronics time to work, but the average output current is still limited.) The high density of the output makes the linac particularly attractive for use in loading storage ring facilities with particles in preparation for particle to particle collisions. The high mass output also makes the device practical for the production of [[antimatter]] particles, which are generally difficult to obtain, being only a small fraction of a target's collision products. These may then be stored and further used to study matter-antimatter annihilation.

===Medical linacs===
[[Image:External beam radiotherapy retinoblastoma nci-vol-1924-300.jpg|thumb|left|Historical image showing Gordon Isaacs, the first patient treated for [[retinoblastoma]] with linear accelerator radiation therapy (in this case an electron beam), in 1957, in the U.S. Other patients had been treated by linac for other diseases since 1953 in the UK. Gordon's right eye was removed on January 11, 1957 because cancer had spread there. His left eye, however, had only a localized tumor that prompted [[Henry Kaplan (physician)|Henry Kaplan]] to treat it with the electron beam.]]
Linac-based [[radiation therapy]] for cancer treatment began with the first patient treated in 1953 in London, UK, at the [[Hammersmith Hospital]], with an 8&nbsp;MV machine built by [[Metropolitan-Vickers]] and installed in 1952, as the first dedicated medical linac.<ref>{{Cite journal|author=Thwaites, DI and Tuohy J|title=Back to the future: the history and development of the clinical linear accelerator|journal=Phys. Med. Biol.|volume=51|year=2006|issue=13 |pages=R343–R36| doi=10.1088/0031-9155/51/13/R20|pmid=16790912 |s2cid=7672187 }}</ref> A short while later in 1954, a 6&nbsp;MV linac was installed in Stanford, USA, which began treatments in 1956.

[[Medical linear accelerators]] accelerate electrons using a tuned-cavity waveguide, in which the RF power creates a [[standing wave]]. Some linacs have short, vertically mounted waveguides, while higher energy machines tend to have a horizontal, longer waveguide and a bending magnet to turn the beam vertically towards the patient. Medical linacs use monoenergetic electron beams between 4 and 25&nbsp;MeV, giving an X-ray output with a spectrum of energies up to and including the electron energy when the electrons are directed at a high-density (such as [[tungsten]]) target. The electrons or X-rays can be used to treat both benign and malignant disease. The LINAC produces a reliable, flexible and accurate radiation beam. The versatility of LINAC is a potential advantage over [[cobalt therapy]] as a treatment tool. In addition, the device can simply be powered off when not in use; there is no source requiring heavy shielding – although the treatment room itself requires considerable shielding of the walls, doors, ceiling etc. to prevent escape of scattered radiation. Prolonged use of high powered (>18&nbsp;MeV) machines can induce a significant amount of radiation within the metal parts of the head of the machine after power to the machine has been removed (i.e. they become an active source and the necessary precautions must be observed).
[[File:Aerial view of a model of a linear accelerator.jpg|thumb|Aerial view of the Little LINAC Model]]
In 2019 a Little Linac model kit, containing 82 building blocks, was developed for children undergoing radiotherapy treatment for cancer. The hope is that building the model will alleviate some of the stress experienced by the child before undergoing treatment by helping them to understand what the treatment entails. The kit was developed by Professor David Brettle, [[Institute of Physics and Engineering in Medicine]] (IPEM) in collaboration with manufacturers Best-Lock Ltd. The model can be seen at the [[Science Museum, London]].

An MR-LINAC is a medical linac integrated with a [[Magnetic resonance imaging]] scanner, which allows for real-time imaging during treatment, as well as patient motion management, and on-table adaptive planning.<ref>{{Cite journal |last1=Ng |first1=John |last2=Gregucci |first2=Fabiana |last3=Pennell |first3=Ryan T. |last4=Nagar |first4=Himanshu |last5=Golden |first5=Encouse B. |last6=Knisely |first6=Jonathan P. S. |last7=Sanfilippo |first7=Nicholas J. |last8=Formenti |first8=Silvia C. |date=2023-01-27 |title=MRI-LINAC: A transformative technology in radiation oncology |journal=Frontiers in Oncology |volume=13 |doi=10.3389/fonc.2023.1117874 |doi-access=free |issn=2234-943X |pmc=9911688 |pmid=36776309}}</ref>