Abstract Body

Treatment planning studies of Very High Energy Electron (VHEE) therapy indicate that a beam energy of 100 MeV should be sufficient for most treatment scenarios. By using the electrons directly, a FLASH dose rate can be achieved far more efficiently than with X-ray therapy. New technology is needed to provide a cost-effective solution that can fit inside existing treatment rooms. We present the design of a VHEE system delivering a 100 MeV electron beam from a one meter linac, using an RF source with 6 MW peak power, as is currently available from commercial modulator systems.

The development of this FLASH VHEE linac draws on innovations in high gradient accelerator research driven by discovery science applications. The operating frequency is chosen to be 11.424 GHz. This high frequency allows the linac to have better RF power efficiency and to sustain higher accelerating gradients. The copper standing wave accelerator has been designed with a 135° phase advance and individually optimized cell geometries, which, alongside cryogenic operation, work to maximize the RF power efficiency.

Figure 1. Cutaway view of the VHEE linac in a cryostat providing 250 W of cooling power at 80 K. Two of the four parallel power distribution manifolds are visible. Incoming RF power is routed through waveguides in the central feedthrough at the back.

The RF power required to reach a 100 MeV/m accelerating gradient in this one meter linac is 19 MW. To achieve this peak power using only a 6 MW RF source, a compact RF pulse compression system is under development. Our approach uses a resonant cavity with a high quality factor to store the energy from a long RF pulse and release it in a short pulse with high peak power, relaxing the requirements on the RF source needed to power this VHEE system.