In 2019, the annual number of cancer cases exceeded 100 million, resulting in 10 million deaths worldwide. Radiation therapy stands out as one of the most effective methods for cancer treatment. Electron beams in the 100-MeV range can reach even deep-seated tumors without the need for surgical intervention. Thanks to novel high-gradient acceleration technologies, clinical facilities for high-energy electron-based irradiation are actively under development. However, the online dosimetry of the delivered dose remains a challenge. In this work, we present a simple and effective solution. We demonstrate that thin YAG screen(s) permanently integrated into the layout of the beamline can be used to characterize the transverse beam distribution shot-to-shot during irradiation. When combined with a beam charge monitor(s), it allows for the prediction of the dose delivered to the target. We benchmark this method using the standard dosimetry routine based on the irradiation of radiochromic films calibrated with an ion chamber.

Corrugated structures have recently been utilized for the time-resolved diagnostics of electron bunches and free-electron-laser (FEL) pulses across several FEL facilities: SwissFEL at PSI and European XFEL at DESY. This approach is simple and cost-effective, based on the self-streaking of electrons with a transverse wakefield enhanced in such structures. In this work, we optimize the design of a corrugated streaker for the wide range of beam parameters of the CERN Linear Electron Accelerator for Research (CLEAR) at CERN. We report on the fabrication of corrugated plates with various corrugation parameters and their initial installation for in-air measurement at CLEAR. Variable polarization streaking can be achieved either by mechanically rotating the plates or by utilizing two pairs of corrugated streakers. Additionally, we emphasize that when streaking in the vertical (or horizontal) direction with one structure, the undesired quadrupole wakefield can be compensated by the second orthogonally oriented streaker. This allows for a significant improvement in the resolution of the method.

The CERN Linear Accelerator for Research (CLEAR) at CERN is a user facility providing a 200 MeV electron beam for accelerator R&D and irradiation studies, including medical applications. In this paper we will outline the most recent improvements in CLEAR operation and beam control and delivery, and describe the upgrades under way, giving an update of their current status. These upgrades include a new front-end for the laser system which will enable an highly flexible time structure, better stability and higher repetition rates, and the implementation of a second beam line which will provide additional testing capability and whose optics has been designed to match user requirements. Finally, we will discuss the proposed future experimental programme of the facility, particularly in view of the novel capabilities provided by the upgrades.

Given the present availability of high-gradient accelerator technology for compact and cost-effective electron linacs in the 100-200 MeV energy range, the interest for Very High Energy Electron (VHEE) radiotherapy (RT) for cancer treatment recently reached an all-time high. Particular significance is assumed by the Ultra-High Dose Rate (UHDR) regime where the so-called FLASH biological effect takes place, in which cancer cells are damaged while healthy tissue is largely spared. VHEE beams from linacs are especially well adapted for FLASH RT, given their penetration depth and the high beam current needed to treat large deep-seated tumours. In recent years, several multidisciplinary user groups carried out a number of studies on VHEE and FLASH RT issues using the CERN Linear Accelerator for Research (CLEAR) user facility, in close collaboration with the local operation team. In this paper we give an overview of such activities and describe the main results of chemical and biological tests aimed at clarifying the damage mechanisms at the root of the FLASH effect and the relevant beam parameters needed to achieve it. We also describe the dedicated systems and methods developed and used in CLEAR for these activities, focusing on recent advances in the crucial aspects of uniform beam delivery and high dose rate real-time dosimetry.