Editing Radiosurgery (section)

===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.