# Linear accelerator machines: from Clinac to AI-imaging linacs, rings and radiosurgery units

Source: https://onco.cc/roadmaps/linac-machines-roadmap/  
OnCo record `linac-machines-roadmap` (Roadmap). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The machine that gives most radiotherapy has been rebuilt every decade or so: sharper beams, then built-in scanners, then rings that treat faster, and now imaging good enough to replan on the spot. This is the chain of models, dated from the regulator's records.

## Summary

Each generation of the medical linear accelerator fixed a limit of the one before. The record of FDA 510(k) clearances dates the steps: Varian's Clinac 20 in 1977; Trilogy in 2003 and Elekta Synergy in 2003, which put a kilovoltage imager on the gantry; TrueBeam in 2011, with energies from 4 MV and later 4D cone-beam CT and motion management; the radiosurgery-focused TrueBeam STx and Edge; Elekta's Versa HD and Infinity under a 2018 clearance; and Harmony in 2021. Halcyon in 2017 enclosed the linac in a fast ring, with mandatory imaging, and Varian claims it uses up to 70 per cent less power and roughly 65 per cent less concrete than a C-arm linac. Ethos in 2020 added same-session adaptive replanning, and the latest generation competes on image quality: HyperSight cone-beam CT on Halcyon, Ethos and TrueBeam, and Elekta Evo, cleared in January 2026, which uses machine-learning scatter correction and iterative reconstruction.

Alongside the general-purpose linac run the specialised designs: CyberKnife on a robot (1999), helical TomoTherapy (2002) and its successor Radixact (2016), the Gamma Knife from Model B (1995 in the FDA record) to Perfexion (2006), Icon (2015) and Esprit (2022), the self-shielded ZAP-X (2017), and makers outside the two large vendors, including United Imaging's CT-integrated uRT-linac 506c (in clinical use since 2019), Our United's TaiChi family, Panacea's Siddharth-II and the Theratron Equinox cobalt unit. The pace is set less by physics than by staffing, bunkers and price, which is why lower-cost and self-shielded designs matter most where machines are scarce.

## Fields

- Kind: Roadmap
- Last checked: 2026-11-04
- Tags: machines-wave3

## Sources

- FDA 510(k) K771358: Clinac 20 (16 August 1977): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K771358
- FDA 510(k) K033343: Trilogy (23 December 2003): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K033343
- FDA 510(k) K032996: Elekta Synergy (23 October 2003): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K032996
- FDA 510(k) K111106: TrueBeam (18 August 2011): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K111106
- FDA 510(k) K140528: TrueBeam, TrueBeam STx, Edge (5 September 2014): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K140528
- FDA 510(k) K182138: Synergy, Infinity, Versa HD (5 September 2018): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K182138
- FDA 510(k) K210500: Elekta Harmony (11 June 2021): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K210500
- FDA 510(k) K170817: Halcyon (27 June 2017): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K170817
- FDA 510(k) K192377: Ethos (10 February 2020): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K192377
- FDA 510(k) K252188: Elekta Evo and Harmony Pro (15 January 2026): https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K252188
- Elekta receives FDA 510(k) clearance for the Elekta Evo linear accelerator (January 2026): https://mfn.se/a/elekta/elekta-receives-fda-510-k-clearance-for-elekta-evo-linear-accelerator
- Varian: Halcyon: https://www.varian.com/products/radiotherapy/treatment-delivery/halcyon
- Yu et al., commissioning a fully integrated CT-linac, the uRT-linac 506c (J Appl Clin Med Phys 2021): https://doi.org/10.1002/acm2.13313

## Connected records

- roadmaps: [MR-linacs and biology-guided radiotherapy: from a cobalt MRI machine to PET-guided beams](https://onco.cc/roadmaps/mr-and-biology-guided-radiotherapy-roadmap/), [Radiotherapy roadmap: X-rays → shaped beams → fewer fractions, particles and FLASH](https://onco.cc/roadmaps/radiation-roadmap/)
- ideas: [An open-hardware radiotherapy machine built for unreliable power and dust](https://onco.cc/ideas/idea-acc-open-hardware-linac/), [Pay for radiotherapy machine uptime, not for the machine](https://onco.cc/ideas/idea-acc-linac-uptime-contracts/)
- fronts: [Devices & Physical Therapies](https://onco.cc/fronts/devices/), [Radiation Therapy](https://onco.cc/fronts/radiation/)
- technologies: [Adaptive radiotherapy (online replanning)](https://onco.cc/technologies/adaptive-radiotherapy/), [AI auto-contouring and adaptive planning](https://onco.cc/technologies/auto-contouring-ai/), [C-arm medical linear accelerators (TrueBeam, Versa HD and others)](https://onco.cc/technologies/c-arm-linac/), [Cobalt-60 teletherapy](https://onco.cc/technologies/cobalt-60-teletherapy/), [CyberKnife robotic radiosurgery](https://onco.cc/technologies/cyberknife/), [Gamma Knife](https://onco.cc/technologies/gamma-knife/), [Global oncology and access in low- and middle-income countries](https://onco.cc/technologies/global-oncology-access/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [In-room imaging for radiotherapy (cone-beam CT, ExacTrac, CT-on-rails, HyperSight)](https://onco.cc/technologies/in-room-imaging-systems/), [Ring-gantry linacs (Halcyon, Ethos)](https://onco.cc/technologies/ring-gantry-linac/), [Rotating gamma and hybrid cobalt systems (Our United TaiChi, MASEP Infini, Akesis Galaxy, GammaPod)](https://onco.cc/technologies/rotating-gamma-radiosurgery-systems/), [SBRT / SABR (stereotactic radiotherapy)](https://onco.cc/technologies/sbrt/), [Stereotactic radiosurgery (Gamma Knife, CyberKnife, linac SRS)](https://onco.cc/technologies/radiosurgery-srs/), [TomoTherapy and Radixact (helical radiotherapy)](https://onco.cc/technologies/tomotherapy/), [ZAP-X gyroscopic radiosurgery](https://onco.cc/technologies/zap-x/)
- companies: [Accuray](https://onco.cc/companies/accuray/), [Best Theratronics](https://onco.cc/companies/best-theratronics/), [Elekta](https://onco.cc/companies/elekta/), [MASEP Medical Science and Technology Development (Shenzhen)](https://onco.cc/companies/masep/), [Our United Corporation](https://onco.cc/companies/our-united/), [Panacea Medical Technologies](https://onco.cc/companies/panacea-medical-technologies/), [United Imaging](https://onco.cc/companies/united-imaging/), [Varian (Siemens Healthineers)](https://onco.cc/companies/varian/), [ZAP Surgical Systems](https://onco.cc/companies/zap-surgical-systems/)
- bottlenecks: [Most of the world has almost no cancer care](https://onco.cc/bottlenecks/b-global-access/), [Not enough oncologists, nurses, pathologists, physicists](https://onco.cc/bottlenecks/b-workforce/), [Surgery and radiotherapy cure most, get least](https://onco.cc/bottlenecks/b-surgery-radiation-innovation/)

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