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Very-high-energy electron therapy

Using very fast electrons instead of photons or protons: a possible way to deliver FLASH-speed radiation to deep tumours from a compact machine.

Electrons in the 100-250 MeV range penetrate deeply, are steerable by magnets, and can be delivered at the ultra-high dose rates associated with the FLASH effect, in principle for a fraction of the cost of a proton facility. Work is at the accelerator-development and preclinical stage at CHUV/CERN, SLAC and elsewhere; the FLASH studies that exist in humans use conventional-energy electrons for skin lesions (for example NCT06549439, completed) or protons. No VHEE patient treatment had been reported by September 2026.

Generic schematic · not to scale · placeholder for the radiation front
Linac head + MLC · Target (PTV) · Gantry arc · Cone-beam CT guidance

How it works

Very-high-energy electrons deposit a relatively flat depth dose that can be shaped magnetically, enabling deep targets and millisecond delivery.

Strengths
  • Potential FLASH sparing at depth
  • Magnetic scanning is fast and precise
  • Cheaper and smaller than proton or carbon facilities
Limitations
  • No clinical machine yet
  • Dosimetry at ultra-high dose rate is unsolved
  • FLASH sparing itself remains unproven in humans

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