Editing Radiosurgery (section)

== Types of radiation source ==
The selection of the proper kind of radiation and device depends on many factors including lesion type, size, and location in relation to critical structures.  Data suggest that similar clinical outcomes are possible with all of the various techniques.  More important than the device used are issues regarding indications for treatment, total dose delivered, fractionation schedule and conformity of the treatment plan.{{cn|date=December 2021}}

=== Gamma Knife ===
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[[File:Dr. B. K. Misra performing Stereotactic Gamma Radiosurgery.jpg|thumb|A doctor performing Gamma Knife Radiosurgery]]
[[Image:Gamma Knife Graphic.jpg|thumb|[[Nuclear Regulatory Commission|NRC]] graphic of the Leksell Gamma Knife]]
A Gamma Knife (also known as the Leksell Gamma Knife) is used to treat [[brain tumors]] by administering high-intensity gamma radiation therapy in a manner that concentrates the radiation over a small volume. The device was invented in 1967 at the Karolinska Institute in [[Stockholm]], Sweden, by [[Lars Leksell]], Romanian-born neurosurgeon Ladislau Steiner, and [[radiobiologist]] Börje Larsson from [[Uppsala University]], Sweden.

A Gamma Knife typically contains 201 [[cobalt-60]] sources of approximately 30&nbsp;[[Curie (unit)|curie]]s each (1.1&nbsp;[[terabecquerel|TBq]]), placed in a hemispheric array in a heavily [[Radiation protection|shielded]] assembly. The device aims [[gamma ray|gamma radiation]] through a target point in the patient's brain.  The patient wears a specialized helmet that is surgically fixed to the skull, so that the brain tumor remains stationary at the target point of the gamma rays. An [[ablation|ablative]] dose of radiation is thereby sent through the tumor in one treatment session, while surrounding brain tissues are relatively spared.

Gamma Knife therapy, like all radiosurgery, uses doses of radiation to kill cancer cells and shrink tumors, delivered precisely to avoid damaging healthy brain tissue. Gamma Knife radiosurgery is able to accurately focus many beams of gamma radiation on one or more tumors. Each individual beam is of relatively low intensity, so the radiation has little effect on intervening brain tissue and is concentrated only at the tumor itself.

Gamma Knife radiosurgery has proven effective for patients with benign or malignant brain tumors up to {{cvt|4|cm|inch}} in size, [[Blood vessel|vascular]] malformations such as an [[arteriovenous malformation]] (AVM), pain, and other functional problems.<ref>{{cite journal | vauthors = Régis J, Bartolomei F, Hayashi M, Chauvel P | title = What role for radiosurgery in mesial temporal lobe epilepsy | journal = Zentralblatt für Neurochirurgie | volume = 63 | issue = 3 | pages = 101–105 | year = 2002 | pmid = 12457334 | doi = 10.1055/s-2002-35824 }}</ref><ref>{{cite journal | vauthors = Kwon Y, Whang CJ | title = Stereotactic Gamma Knife radiosurgery for the treatment of dystonia | journal = Stereotactic and Functional Neurosurgery | volume = 64 | issue = Suppl 1 | pages = 222–227 | year = 1995 | pmid = 8584831 | doi = 10.1159/000098782 }}</ref><ref>{{cite journal | vauthors = Donnet A, Valade D, Régis J | title = Gamma knife treatment for refractory cluster headache: prospective open trial | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 76 | issue = 2 | pages = 218–221 | date = February 2005 | pmid = 15654036 | pmc = 1739520 | doi = 10.1136/jnnp.2004.041202 }}</ref><ref>{{cite journal | vauthors = Herman JM, Petit JH, Amin P, Kwok Y, Dutta PR, Chin LS | title = Repeat gamma knife radiosurgery for refractory or recurrent trigeminal neuralgia: treatment outcomes and quality-of-life assessment | journal = International Journal of Radiation Oncology, Biology, Physics | volume = 59 | issue = 1 | pages = 112–116 | date = May 2004 | pmid = 15093906 | doi = 10.1016/j.ijrobp.2003.10.041 }}</ref>  For treatment of trigeminal neuralgia the procedure may be used repeatedly on patients.

Acute complications following Gamma Knife radiosurgery are rare,<ref>{{cite journal | vauthors = Chin LS, Lazio BE, Biggins T, Amin P | title = Acute complications following gamma knife radiosurgery are rare | journal = Surgical Neurology | volume = 53 | issue = 5 | pages = 498–502; discussion 502 | date = May 2000 | pmid = 10874151 | doi = 10.1016/S0090-3019(00)00219-6 }}</ref> and complications are related to the condition being treated.<ref>{{cite journal | vauthors = Stafford SL, Pollock BE, Foote RL, Link MJ, Gorman DA, Schomberg PJ, Leavitt JA | title = Meningioma radiosurgery: tumor control, outcomes, and complications among 190 consecutive patients | journal = Neurosurgery | volume = 49 | issue = 5 | pages = 1029–37; discussion 1037–8 | date = November 2001 | pmid = 11846894 | doi = 10.1097/00006123-200111000-00001 | s2cid = 13646182 }}</ref><ref>{{cite journal | vauthors = Cho DY, Tsao M, Lee WY, Chang CS | title = Socioeconomic costs of open surgery and gamma knife radiosurgery for benign cranial base tumors | journal = Neurosurgery | volume = 58 | issue = 5 | pages = 866–73; discussion 866–73 | date = May 2006 | pmid = 16639320 | doi = 10.1227/01.NEU.0000209892.42585.9B | s2cid = 38660074 }}</ref>

=== Linear accelerator-based therapies ===
{{Main|Megavoltage X-rays}}

A linear accelerator (linac) produces x-rays from the impact of accelerated electrons striking a high ''z'' target, usually tungsten. The process is also referred to as "x-ray therapy" or "photon therapy."  The emission head, or "[[Gantry crane|gantry]]", is mechanically rotated around the patient in a full or partial circle. The table where the patient is lying, the "couch", can also be moved in small linear or angular steps. The combination of the movements of the gantry and of the couch allow the computerized planning of the volume of tissue that is going to be irradiated. Devices with a high energy of 6&nbsp;MeV are commonly used for the treatment of the brain, due to the depth of the target. The diameter of the energy beam leaving the emission head can be adjusted to the size of the lesion by means of [[collimator]]s. They may be interchangeable orifices with different diameters, typically varying from 5 to 40&nbsp;mm in 5&nbsp;mm steps, or multileaf collimators, which consist of a number of metal leaflets that can be moved dynamically during treatment in order to shape the radiation beam to conform to the mass to be ablated. {{As of|2017}} Linacs were capable of achieving extremely narrow beam geometries, such as 0.15 to 0.3&nbsp;mm. Therefore, they can be used for several kinds of surgeries which hitherto had been carried out by open or endoscopic surgery, such as for trigeminal neuralgia. Long-term follow-up data has shown it to be as effective as radiofrequency ablation, but inferior to surgery in preventing the recurrence of pain.{{cn|date=December 2021}}

The first such systems were developed by [[John R. Adler]], a [[Stanford University]] professor of neurosurgery and radiation oncology, and Russell and Peter Schonberg at Schonberg Research, and commercialized under the brand name CyberKnife.

=== Proton beam therapy ===
{{Main|Proton therapy}}

Protons may also be used in radiosurgery in a procedure called '''Proton Beam Therapy''' (PBT) or [[proton therapy]]. Protons are extracted from proton donor materials by a medical [[synchrotron]] or [[cyclotron]], and accelerated in successive transits through a circular, evacuated conduit or cavity, using powerful magnets to shape their path, until they reach the energy required to just traverse a human body, usually about 200&nbsp;MeV. They are then released toward the region to be treated in the patient's body, the irradiation target. In some machines, which deliver protons of only a specific energy, a custom mask made of plastic is interposed between the beam source and the patient to adjust the beam energy to provide the appropriate degree of penetration. The phenomenon of the [[Bragg peak]] of ejected protons gives proton therapy advantages over other forms of radiation, since most of the proton's energy is deposited within a limited distance, so tissue beyond this range (and to some extent also tissue inside this range) is spared from the effects of radiation. This property of protons, which has been called the "[[depth charge]] effect" by analogy to the explosive weapons used in anti-submarine warfare, allows for conformal dose distributions to be created around even very irregularly shaped targets, and for higher doses to targets surrounded or backstopped by radiation-sensitive structures such as the [[optic chiasm]] or brainstem. The development of "intensity modulated" techniques allowed similar conformities to be attained using linear accelerator radiosurgery.{{cn|date=December 2021}}

{{As of|2013}} there was no evidence that proton beam therapy is better than any other types of treatment in most cases, except for a "handful of rare pediatric cancers". Critics, responding to the increasing number of very expensive PBT installations, spoke of a "medical [[arms race]]"  and "crazy medicine and unsustainable public policy".<ref name="medscape.com">{{cite web |url=http://www.medscape.com/viewarticle/778466 |title=Uncertainty About Proton-Beam Radiotherapy Lingers |website=Medscape|date=30 January 2013  |author=Roxanne Nelson |access-date= 22 March 2017}}</ref>