IntroductionRadiosurgery operates bydirecting tightly focusedbeams of ionizing radiationwith high precision frommultiple directions atintracranial and extracranialtumors and other lesions.The beam paths converge inthe target volume,delivering a lethalcumulative dose ofradiation, while exposingadjacent healthy tissue to amuch smaller level ofradiation.
Medical usesRadiosurgery has beenespecially helpful for thelocalized, highly precisetreatment of braintumors. Due to the steepfall off of the irradiationfields from the center ofthe target to be ablated,normal structures such asthe brain, and othervascular and neuralstructures around it, arerelatively spared.
Gamma KnifeGamma Kniferadiosurgery has proveneffective for patients withbenign or malignant braintumors up to 4centimeters in size,vascular malformationssuch as an arteriovenousmalformation (AVM), painor other functionalproblems.
Linear accelerator based therapiesLinear accelerators emit highenergy X-rays, usuallyreferred to as "X-raytherapy" or "photontherapy." The term "gammaray" is usually reserved forphotons that are emittedfrom a radioisotope such ascobalt-60. Such radiation isnot substantially differentfrom that emitted by highvoltage accelerators.
Proton beam therapyProtons may also be used inradiosurgery in a procedurecalled Proton Beam Therapy (PBT)or simply proton therapy. Protonsare produced by a medicalsynchrotron or cyclotron,extracting them from protondonor materials and acceleratingthem in successive travelsthrough a circular, evacuatedconduit or cavity, using powerfulmagnets, until they reachsufficient energy to enable themto approximately traverse ahuman body, then stop.