C-arm medical linear accelerators (TrueBeam, Versa HD and others)

A medical linac fires electrons down a copper waveguide driven by microwaves until they reach several million electronvolts, bends them through a magnet and either slams them into a tungsten target to make photons or scatters them directly as an electron beam. The head carries a multileaf collimator whose tungsten leaves shape the field and modulate its intensity, and the whole assembly rotates on a C-shaped gantry around a couch that moves in six degrees of freedom. A kilovoltage imager on a side arm takes radiographs and cone-beam CT for image guidance, and surface cameras or breath-hold systems handle motion. The first clinical linac treated a patient in London in 1953; today Varian's TrueBeam and Edge and Elekta's Versa HD, Infinity and Harmony are the dominant models, with Chinese and Indian makers offering lower-cost units.

The C-arm is versatile: photons at several energies, electrons for skin and superficial targets, non-coplanar beams for brain radiosurgery, and every technique from palliative fields to VMAT and SBRT. Its limits are cost, a shielded bunker, a workforce of physicists and therapists, and mechanical tolerances that require daily quality assurance. Ring-gantry, helical and robotic designs trade some of that flexibility for speed, integrated imaging or steeper dose fall-off.