Development of a Novel Fibre Optic Beam Monitor for FLASH Radiotherapy

A recently discovered phenomena in the field of radiation oncology eludes to reduced radiation-induced toxicities in healthy tissue following irradiation at ultrahigh dose rates (> 40 Gy/s, compared to ~ 0.05 Gy/s for conventional radiotherapy), whilst maintaining the same level of damage to the tumour. This has been coined the FLASH effect. The potential use of Very High Energy Electron (VHEE) beams with energies between 50-250 MeV for radiotherapy has gained interest due to advances in high-gradient electron accelerator technology and the potential to use these VHEE beams at UHDR to elicit the FLASH effect in deep-seated tumours. However one major technological challenge facing the clinical implementation of FLASH radiotherapy is that ionisation chambers - used for both reference dosimetry and online beam monitoring - exhibit a non-linear response in these UHDR conditions, therefore alternative detector and dosimetry technology is required. A novel detector consisting of two orthogonal arrays of silica fibres is under development to provide real-time beam profile and dose monitoring of VHEE beams at UHDR. Extensive tests have been conducted with an early prototype at the CERN Linear Electron Accelerator for Research (CLEAR) to test the detectors capability of providing real-time dose prediction and pulse-pulse beam profile measurements of 200 MeV electrons.