Editing Radiosurgery (section)

=== 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>