Editing Radiosurgery (section)

==History==
Stereotactic radiosurgery was first developed in 1949 by the Swedish neurosurgeon Lars Leksell to treat small targets in the brain that were not amenable to conventional surgery. The initial stereotactic instrument he conceived used probes and electrodes.<ref>{{cite journal| vauthors = Leksell L |title=A stereotaxic apparatus for intracerebral surgery|journal=Acta Chirurgica Scandinavica|year=1949|volume=99|pages=229}}</ref> The first attempt to supplant the electrodes with radiation was made in the early fifties, with [[x-ray]]s.<ref>{{cite journal | vauthors = Leksell L | title = The stereotaxic method and radiosurgery of the brain | journal = Acta Chirurgica Scandinavica | volume = 102 | issue = 4 | pages = 316–319 | date = December 1951 | pmid = 14914373 }}</ref> The principle of this instrument was to hit the intra-cranial target with narrow beams of radiation from multiple directions. The beam paths converge in the target volume, delivering a lethal cumulative dose of radiation there, while limiting the dose to the adjacent healthy tissue. Ten years later significant progress had been made, due in considerable measure to the contribution of the physicists Kurt Liden and Börje Larsson.<ref>{{cite journal | vauthors = Larsson B, Leksell L, Rexed B, Sourander P, Mair W, Andersson B | title = The high-energy proton beam as a neurosurgical tool | journal = Nature | volume = 182 | issue = 4644 | pages = 1222–1223 | date = November 1958 | pmid = 13590280 | doi = 10.1038/1821222a0 | s2cid = 4163683 | bibcode = 1958Natur.182.1222L }}</ref>  At this time, stereotactic [[proton]] beams had replaced the x-rays.<ref>{{cite journal | vauthors = Leksell L, Larsson B, Andersson B, Rexed B, Sourander P, Mair W | title = Lesions in the depth of the brain produced by a beam of high energy protons | journal = Acta Radiologica | volume = 54 | issue = 4 | pages = 251–264 | date = October 1960 | pmid = 13760648 | doi = 10.3109/00016926009172547 | doi-access = free }}</ref> The heavy particle beam presented as an excellent replacement for the surgical knife, but the [[synchrocyclotron]] was too clumsy. Leksell proceeded to develop a practical, compact, precise and simple tool which could be handled by the surgeon himself. In 1968 this resulted in the Gamma Knife, which was installed at the [[Karolinska Institutet|Karolinska Institute]] and consisted of several [[cobalt-60]] [[radioactivity|radioactive]] sources placed in a kind of helmet with central channels for irradiation with gamma rays.<ref>{{cite journal | vauthors = Leksell L | title = Stereotactic radiosurgery | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 46 | issue = 9 | pages = 797–803 | date = September 1983 | pmid = 6352865 | pmc = 1027560 | doi = 10.1136/jnnp.46.9.797 }}</ref> This prototype was designed to produce slit-like radiation lesions for functional neurosurgical procedures to treat pain, movement disorders, or behavioral disorders that did not respond to conventional treatment. The success of this first unit led to the construction of a second device, containing 179 cobalt-60 sources. This second Gamma Knife unit was designed to produce spherical lesions to treat brain tumors and intracranial [[arteriovenous malformation]]s (AVMs).<ref>{{cite journal | vauthors = Wu A, Lindner G, Maitz AH, Kalend AM, Lunsford LD, Flickinger JC, Bloomer WD | title = Physics of gamma knife approach on convergent beams in stereotactic radiosurgery | journal = International Journal of Radiation Oncology, Biology, Physics | volume = 18 | issue = 4 | pages = 941–949 | date = April 1990 | pmid = 2182583 | doi = 10.1016/0360-3016(90)90421-f }}</ref> Additional units were installed in the 1980s all with 201 cobalt-60 sources.<ref>{{cite journal | vauthors = Walton L, Bomford CK, Ramsden D | title = The Sheffield stereotactic radiosurgery unit: physical characteristics and principles of operation | journal = The British Journal of Radiology | volume = 60 | issue = 717 | pages = 897–906 | date = September 1987 | pmid = 3311273 | doi = 10.1259/0007-1285-60-717-897 }}</ref>

In parallel to these developments, a similar approach was designed for a [[linear particle accelerator]] or Linac. Installation of the first 4&nbsp;[[electronvolt|MeV]] clinical linear accelerator began in June 1952 in the Medical Research Council (MRC) Radiotherapeutic Research Unit at the [[Hammersmith Hospital]], London.<ref>{{cite journal | vauthors = Fry DW, R-Shersby-Harvie RB | title = A traveling-wave linear accelerator for 4-MeV. electrons | journal = Nature | volume = 162 | issue = 4126 | pages = 859–861 | date = November 1948 | pmid = 18103121 | doi = 10.1038/162859a0 | s2cid = 4075004 | bibcode = 1948Natur.162..859F }}</ref> The system was handed over for physics and other testing in February 1953 and began to treat patients on 7 September that year. Meanwhile, work at the Stanford Microwave Laboratory led to the development of a 6 MeV accelerator, which was installed at Stanford University Hospital, California, in 1956.<ref>{{cite journal | vauthors = Bernier J, Hall EJ, Giaccia A | title = Radiation oncology: a century of achievements | journal = Nature Reviews. Cancer | volume = 4 | issue = 9 | pages = 737–747 | date = September 2004 | pmid = 15343280 | doi = 10.1038/nrc1451 | s2cid = 12382751 }}</ref> Linac units quickly became favored devices for conventional fractionated [[radiation therapy|radiotherapy]] but it lasted until the 1980s before dedicated Linac radiosurgery became a reality. In 1982, the Spanish neurosurgeon J. Barcia-Salorio began to evaluate the role of cobalt-generated and then Linac-based photon radiosurgery for the treatment of AVMs and [[epilepsy]].<ref>{{cite journal | vauthors = Barcia-Salorio JL, Herandez G, Broseta J, Gonzalez-Darder J, Ciudad J | title = Radiosurgical treatment of carotid-cavernous fistula | journal = Applied Neurophysiology | volume = 45 | issue = 4–5 | pages = 520–522 | year = 1982 | pmid = 7036892 | doi = 10.1159/000101675 }}</ref> In 1984, Betti and Derechinsky described a Linac-based radiosurgical system.<ref>{{Cite book| vauthors = Betti OO |title=Advances in Stereotactic and Functional Neurosurgery 6 |chapter=Hyperselective Encephalic Irradiation with Linear Accelerator|journal=[[Acta Neurochirurgica Supplement]] |year=1984|volume=33|pages=385–390|doi=10.1007/978-3-7091-8726-5_60|isbn=978-3-211-81773-5}}</ref> Winston and Lutz further advanced Linac-based radiosurgical prototype technologies by incorporating an improved stereotactic positioning device and a method to measure the accuracy of various components.<ref>{{cite journal | vauthors = Winston KR, Lutz W | title = Linear accelerator as a neurosurgical tool for stereotactic radiosurgery | journal = Neurosurgery | volume = 22 | issue = 3 | pages = 454–464 | date = March 1988 | pmid = 3129667 | doi = 10.1227/00006123-198803000-00002 }}</ref> Using a modified Linac, the first patient in the United States was treated in Boston [[Brigham and Women's Hospital]] in February 1986.{{cn|date=December 2021}}

===21st century===
Technological improvements in medical imaging and computing have led to increased clinical adoption of stereotactic radiosurgery and have broadened its scope in the 21st century.<ref>{{Cite book| vauthors = De Salles A |title=Reconstructive Neurosurgery|chapter=Radiosurgery from the brain to the spine: 20 years experience|journal=[[Acta Neurochirurgica. Supplement]] |year=2008|volume=101|pages=163–168|pmid=18642653|doi=10.1007/978-3-211-78205-7_28|series=Acta Neurochirurgica Supplementum|isbn=978-3-211-78204-0}}</ref><ref>{{cite journal | vauthors = Timmerman R, McGarry R, Yiannoutsos C, Papiez L, Tudor K, DeLuca J, Ewing M, Abdulrahman R, DesRosiers C, Williams M, Fletcher J | display-authors = 6 | title = Excessive toxicity when treating central tumors in a phase II study of stereotactic body radiation therapy for medically inoperable early-stage lung cancer | journal = Journal of Clinical Oncology | volume = 24 | issue = 30 | pages = 4833–4839 | date = October 2006 | pmid = 17050868 | doi = 10.1200/JCO.2006.07.5937 | doi-access = free }}</ref> The localization accuracy and precision that are implicit in the word "stereotactic" remain of utmost importance for radiosurgical interventions and are significantly improved via [[image-guided surgery|image-guidance]] technologies such as the [[N-localizer]]<ref>{{cite book | vauthors = Galloway Jr RL | veditors = Golby AJ | title = Image-Guided Neurosurgery | chapter = Introduction and Historical Perspectives on Image-Guided Surgery | pages = 2–4 | publisher = Elsevier | location = Amsterdam | year = 2015 | isbn=978-0-12-800870-6|doi=10.1016/B978-0-12-800870-6.00001-7}}</ref> and Sturm-Pastyr localizer<ref>{{cite journal | vauthors = Sturm V, Pastyr O, Schlegel W, Scharfenberg H, Zabel HJ, Netzeband G, Schabbert S, Berberich W | display-authors = 6 | title = Stereotactic computer tomography with a modified Riechert-Mundinger device as the basis for integrated stereotactic neuroradiological investigations | journal = Acta Neurochirurgica | volume = 68 | issue = 1–2 | pages = 11–17 | year = 1983 | pmid = 6344559 | doi = 10.1007/BF01406197 | s2cid = 38864553 }}</ref> that were originally developed for [[stereotactic surgery]].

In the 21st century the original concept of radiosurgery  expanded to include treatments comprising up to five [[Dose fractionation|fractions]], and stereotactic radiosurgery has been redefined as a distinct [[neurosurgical]] discipline that utilizes externally generated [[ionizing radiation]] to inactivate or eradicate defined targets, typically in the head or spine, without the need for a surgical incision.<ref name=barnett>{{cite journal | vauthors = Barnett GH, Linskey ME, Adler JR, Cozzens JW, Friedman WA, Heilbrun MP, Lunsford LD, Schulder M, Sloan AE | display-authors = 6 | title = Stereotactic radiosurgery--an organized neurosurgery-sanctioned definition | journal = Journal of Neurosurgery | volume = 106 | issue = 1 | pages = 1–5 | date = January 2007 | pmid = 17240553 | doi = 10.3171/jns.2007.106.1.1 | s2cid = 1007105 }}</ref> Irrespective of the similarities between the concepts of stereotactic radiosurgery and fractionated radiotherapy the mechanism to achieve treatment is subtly different, although both treatment modalities are reported to have identical outcomes for certain indications.<ref name=combs>{{cite journal | vauthors = Combs SE, Welzel T, Schulz-Ertner D, Huber PE, Debus J | title = Differences in clinical results after LINAC-based single-dose radiosurgery versus fractionated stereotactic radiotherapy for patients with vestibular schwannomas | journal = International Journal of Radiation Oncology, Biology, Physics | volume = 76 | issue = 1 | pages = 193–200 | date = January 2010 | pmid = 19604653 | doi = 10.1016/j.ijrobp.2009.01.064 }}</ref> Stereotactic radiosurgery has a greater emphasis on delivering precise, high doses to small areas, to destroy target tissue while preserving adjacent normal tissue. The same principle is followed in conventional radiotherapy although lower dose rates spread over larger areas are more likely to be used (for example as in [[Radiation therapy#Volumetric modulated arc therapy (VMAT)|VMAT]] treatments). Fractionated radiotherapy relies more heavily on the different [[radiosensitivity]] of the target and the surrounding normal tissue to the [[Absorbed dose|total accumulated radiation dose]].<ref name=barnett/> Historically, the field of fractionated radiotherapy evolved from the original concept of stereotactic radiosurgery following discovery of the principles of [[radiobiology]]: repair, reassortment, repopulation, and reoxygenation.<ref>{{cite journal | vauthors = Bernier J, Hall EJ, Giaccia A | title = Radiation oncology: a century of achievements | journal = Nature Reviews. Cancer | volume = 4 | issue = 9 | pages = 737–747 | date = September 2004 | pmid = 15343280 | doi = 10.1038/nrc1451 | s2cid = 12382751 }}</ref> Today, both treatment techniques are complementary, as tumors that may be resistant to fractionated radiotherapy may respond well to radiosurgery, and tumors that are too large or too close to critical organs for safe radiosurgery may be suitable candidates for fractionated radiotherapy.<ref name=combs />

Today, both Gamma Knife and Linac radiosurgery programs are commercially available worldwide. While the Gamma Knife is dedicated to radiosurgery, many Linacs are built for conventional fractionated radiotherapy and require additional technology and expertise to become dedicated radiosurgery tools. There is not a clear difference in efficacy between these different approaches.<ref>{{cite report |url= http://eprints.hta.lbg.ac.at/901/ |title=Gamma Knife versus adapted linear accelerators: A comparison of two radiosurgical applications | vauthors = Mathis S, Eisner W |date=6 October 2010 |issn=1993-0488|eissn=1993-0496|series=HTA-Projektbericht 47}}</ref><ref>{{cite book | vauthors = McDermott MW |title=Radiosurgery |date=2010 |publisher=Karger Medical and Scientific Publishers |isbn=9783805593656 |page=196 |url=https://books.google.com/books?id=Ya86AQAAQBAJ&pg=PA196 |language=en}}</ref> The major manufacturers, [[Varian Medical Systems|Varian]] and [[Elekta]] offer dedicated radiosurgery Linacs as well as machines designed for conventional treatment with radiosurgery capabilities. Systems designed to complement conventional Linacs with beam-shaping technology, treatment planning, and image-guidance tools to provide.<ref>{{cite book | vauthors = Schoelles KM, Uhl S, Launders J, Inamdar R, Bruening W, Sullivan N, Tipton KN |title=Stereotactic Body Radiation Therapy |date=2011 |publisher=Agency for Healthcare Research and Quality (US) |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK55712/ |language=en |chapter=Currently Marketed Devices for SBRT |pmid=21735562}}</ref> An example of a dedicated radiosurgery Linac is the [[Cyberknife (device)|CyberKnife]], a compact Linac mounted onto a robotic arm that moves around the patient and irradiates the tumor from a large set of fixed positions, thereby mimicking the Gamma Knife concept.