# Electron beam therapy systems (linac electrons, total skin electron units, mobile electron IORT)

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

## TL;DR

Electron beams stop within a few centimetres of the skin, so they treat surface tumours, scars and the whole skin without reaching the organs underneath. Most linacs make them; special set-ups spread them over the entire body or deliver them during surgery.

## Summary

When a medical linac is switched from photon to electron mode the tungsten target is retracted and the electron pencil beam is spread by scattering foils and shaped by a metal applicator and a lead or Cerrobend cut-out placed close to the skin. Electrons of 4 to 20 MeV deposit dose fairly evenly to a depth of roughly a third of their energy in centimetres, then fall away sharply, which suits chest-wall and scar boosts in breast cancer, skin cancers of the nose, ear and eyelid, keloids, and superficial lymph nodes. Total skin electron beam therapy, developed at Stanford, stands the patient several metres from the machine in a set of poses while a degraded low-energy beam treats the entire skin surface for mycosis fungoides and other cutaneous lymphomas. Mobile electron linacs such as IntraOp's Mobetron bring a 6 to 12 MeV electron beam into the operating theatre for intraoperative radiotherapy of the tumour bed, sparing the shielded bunker.

Against superficial and orthovoltage X-rays, electrons treat thicker targets and spare deeper tissue; against protons they are far cheaper and available on almost every linac, but the dose edge is blurrier, bone and air cavities perturb it, and ring-gantry machines such as Halcyon do not offer electrons at all. Very high energy electrons of 100 MeV and above, which would reach deep tumours, exist only in research accelerators.

## Fields

- Kind: Technology
- Status: standard-of-care
- Last checked: 2026-09-17
- Tags: machines-wave2
- Principle: The accelerated electron beam is scattered and collimated without a photon target, depositing dose to a depth set by its energy and then falling off rapidly, so superficial targets are treated with little exit dose.
- Since: 1950
- Strengths: Sharp dose fall-off spares organs under the skin; Available on most C-arm linacs; Total skin and intraoperative variants for special needs
- Limitations: Cannot reach deep tumours; Bone and air cavities distort the dose; Not offered on ring-gantry linacs

## Sources

- IntraOp: Mobetron mobile electron IORT: https://intraop.com/mobetron/
- Wikipedia: electron therapy: https://en.wikipedia.org/wiki/Electron_therapy

## Connected records

- technologies: [C-arm medical linear accelerators (TrueBeam, Versa HD and others)](https://onco.cc/technologies/c-arm-linac/), [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/), [Intraoperative radiotherapy (IORT)](https://onco.cc/technologies/intraoperative-radiotherapy/), [Superficial and orthovoltage radiotherapy for skin cancer](https://onco.cc/technologies/superficial-radiotherapy/), [Total skin electron beam therapy](https://onco.cc/technologies/total-skin-electron-therapy/)
- cancers: [Basal cell carcinoma](https://onco.cc/cancers/basal-cell-carcinoma/), [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [Cutaneous T-cell lymphoma (mycosis fungoides and Sezary syndrome)](https://onco.cc/cancers/cutaneous-t-cell-lymphoma/), [Merkel cell carcinoma](https://onco.cc/cancers/merkel-cell-carcinoma/), [Skin cancer (all types)](https://onco.cc/cancers/skin-cancer/)
- fronts: [Devices & Physical Therapies](https://onco.cc/fronts/devices/), [Radiation Therapy](https://onco.cc/fronts/radiation/)
- companies: [Elekta](https://onco.cc/companies/elekta/), [IntraOp Medical](https://onco.cc/companies/intraop-medical/), [Varian (Siemens Healthineers)](https://onco.cc/companies/varian/)

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