Editing Radiosurgery (section)

=== 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.