Direct Measurements of Energy Spectra Under Ultra-high Dose Rate Electron Beam Conditions

Ultra-high dose rate radiotherapy (FLASH-RT) is a highly promising approach to cancer treatment, utilising ionising radiation. This innovative technique delivers the treatment dose in less than 200 ms, inducing the “FLASH effect”, which spares healthy tissue while retaining tumour control. This type of dose delivery presents significant challenges for accurate dose and energy measurement, especially for a single radiation pulse. In this work, we present a method for direct measurements of the energy spectrum using a permanent magnet electron energy spectrometer, designed to evaluate the energy distribution of electron beams at a wide range of dose rates. The preliminary results obtained in the AQURE FLASH RT accelerator dedicated to FLASH research indicate differences in the energy spectra of beams, which differ in dose rate. This method makes it possible to obtain the energy spectra of even a single pulse, and to determine its most probable and average energy of the electron beams. Abstract Published by the Jagiellonian University 2026 authors