Power and beam dynamics optimization of a compact linac for FLASH radiotherapy with prospects for VHEE

Radiotherapy represents a cornerstone of cancer treatment, playing a central role in tumor control and volume reduction. Recently, the delivery of UltraHigh Dose Rates (UHDR) has emerged as a promising method to enhance healthy tissue sparing via the FLASH effect (FAVAUDON V. et al., Sci. Transl. Med., 6 (2014) 245ra93), while maintaining tumor toxicity. When combined with Very High Energy Electrons (VHEE), this modality allows for the effective targeting of deep-seated et al., Med. Phys., 42 (2015) 2615). This work, conducted within the framework of the SAFEST project at Sapienza University (GIULIANO L. et al., Front. Oncol., 15 (2025) 1516576; FAILLACE L. et al., Phys. Med., 104 (2022) 149), investigates the design of a compact electron LINAC suitable for a hospital environment. We present a comprehensive optimization of the RF power system and beam dynamics for a Cband accelerator capable of reaching 100 MeV in a 4 m footprint. The accelerator exploits a 20 MW klystron coupled with a pulse compressor, and achieves the high peak currents required for UHDR thanks to a thermionic triode gun. Furthermore, two beam delivery strategies -passive scattering and pencil beam scanning-are analyzed to validate the clinical feasibility of this technology.