Speaker
Description
Very High Energy Electrons (VHEE) are an emerging radiotherapy modality offering magnetic steering and focusing for conformal treatments, with potential for compact, cost-efficient clinical systems. VHEE beams may also enable Ultra-High Dose Rate (UHDR) delivery for the FLASH effect, which can selectively spare healthy tissue while maintaining tumour toxicity. A key challenge is achieving transversely uniform VHEE dose at UHDR, as current magnets cannot scan large tumour volumes within FLASH timescales (~0.1 s). Conventional dual-scattering systems—using a pre-scatterer for magnification and a Gaussian scatterer for flattening—are unsuitable at VHEE energies, generating substantial photon contamination unless the beamline is greatly extended.
This work replaces the pre-scatterer with a quadrupole lattice that magnetically enlarges the beam while reducing Bremsstrahlung. RF-Track and TOPAS simulations show that an optimised quadrupole-scatterer design produces a 75 mm uniform field and reduces photon yield by 94.5% compared with dual-scattering. BDSIM confirms the modelling. Experimental validation at CLEAR at CERN is in preparation, and an optimiser is being developed to design quad-scatterer systems for generic VHEE machines using existing quadrupoles. These results suggest that magnetic beam magnification upstream of a Gaussian scatterer is a promising route to FLASH-compatible VHEE therapy with reduced secondary radiation and improved dose conformity.
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