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

Source: https://onco.cc/technologies/c-arm-linac/  
OnCo record `c-arm-linac` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The standard radiotherapy machine: an electron accelerator in a rotating arm that makes high-energy X-rays or electron beams, shapes them with moving metal leaves, and takes a CT of the patient before each dose. Most people who have radiotherapy are treated on one.

## Summary

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.

## Fields

- Kind: Technology
- Status: standard-of-care
- Last checked: 2026-09-17
- Tags: machines-wave
- Principle: Microwave-driven acceleration of electrons produces megavoltage X-rays or electron beams; a rotating gantry, multileaf collimator and on-board kilovoltage imaging shape and aim the dose to the target seen on the day.
- Since: 1953
- Strengths: Treats almost every site and technique on one machine; Photon and electron beams at several energies; Integrated cone-beam CT and surface guidance
- Limitations: Needs a shielded bunker and skilled staff; Daily quality assurance of mechanical tolerances; Throughput limited by set-up and imaging time

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Linear_particle_accelerator
- Varian: TrueBeam: https://www.varian.com/products/radiotherapy/treatment-delivery/truebeam
- Elekta: linear accelerators: https://www.elekta.com/products/radiation-therapy/

## Connected records

- technologies: [Cobalt-60 teletherapy](https://onco.cc/technologies/cobalt-60-teletherapy/), [CyberKnife robotic radiosurgery](https://onco.cc/technologies/cyberknife/), [Electron beam therapy systems (linac electrons, total skin electron units, mobile electron IORT)](https://onco.cc/technologies/electron-beam-therapy-systems/), [FLASH research accelerators (Oriatron, Mobetron FLASH, ProBeam FLASH)](https://onco.cc/technologies/flash-research-accelerators/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [Oncology information and record-and-verify systems (ARIA, MOSAIQ)](https://onco.cc/technologies/oncology-information-systems/), [Patient positioning and surface guidance systems (AlignRT, Catalyst, ExacTrac Dynamic)](https://onco.cc/technologies/patient-positioning-surface-guidance-systems/), [Proton therapy machines: cyclotrons, synchrotrons and single-room systems](https://onco.cc/technologies/proton-therapy-systems/), [Radiotherapy access and the global machine gap](https://onco.cc/technologies/radiotherapy-access-gap/), [Radiotherapy QA phantoms and dosimeters (Sun Nuclear, IBA Dosimetry, PTW)](https://onco.cc/technologies/radiotherapy-qa-phantoms-dosimeters/), [Respiratory motion management (4D-CT, gating, breath-hold, tracking)](https://onco.cc/technologies/respiratory-motion-management/), [Ring-gantry linacs (Halcyon, Ethos)](https://onco.cc/technologies/ring-gantry-linac/), [SBRT / SABR (stereotactic radiotherapy)](https://onco.cc/technologies/sbrt/), [Surface-guided radiotherapy (SGRT)](https://onco.cc/technologies/surface-guided-radiotherapy/), [TomoTherapy and Radixact (helical radiotherapy)](https://onco.cc/technologies/tomotherapy/), [Volumetric modulated arc therapy (VMAT)](https://onco.cc/technologies/vmat/), [ZAP-X gyroscopic radiosurgery](https://onco.cc/technologies/zap-x/)
- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [Cervical cancer](https://onco.cc/cancers/cervical/), [Colorectal cancer](https://onco.cc/cancers/colorectal/), [Glioma & glioblastoma](https://onco.cc/cancers/glioblastoma/), [Head and neck squamous cell carcinoma](https://onco.cc/cancers/head-and-neck/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Oesophageal cancer](https://onco.cc/cancers/esophageal/), [Prostate cancer](https://onco.cc/cancers/prostate/)
- fronts: [Devices & Physical Therapies](https://onco.cc/fronts/devices/), [Radiation Therapy](https://onco.cc/fronts/radiation/)
- companies: [Elekta](https://onco.cc/companies/elekta/), [Varian (Siemens Healthineers)](https://onco.cc/companies/varian/)
- terms: [IMRT / IGRT / VMAT (modern external beam radiotherapy)](https://onco.cc/terms/imrt-term/), [Organs at risk and dose constraints](https://onco.cc/terms/organs-at-risk/)

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