Ultra-high-dose rate FLASH radiotherapy

Ultra-High-Dose Rate (UHDR) FLASH radiotherapy is an emerging modality that has demonstrated the potential to revolutionize cancer treatment by delivering radiation doses at rates several orders of magnitude higher than conventional therapies. This chapter offers a comprehensive overview of the FLASH effect, a phenomenon wherein ultra-rapid dose delivery reduces toxicity to healthy tissues while maintaining tumor control. The state of the art is reviewed with emphasis on radiobiological evidence, dosimetric challenges, and current technologies, particularly with electron beams. A focus is placed on the characterization and dosimetry using Gafchromic films and diamond detectors under FLASH conditions, as well as on the modeling of the FLASH-modifying factor (FMF) to estimate clinical impact. The chapter also explores the potential of Very High Energy Electrons (VHEE) for deep-seated tumors and discusses novel accelerator designs, including the compact C-band linac developed by Sapienza and INFN. By integrating radiobiology, dosimetry, and accelerator physics, the chapter outlines the technological and clinical steps required to bring FLASH therapy from preclinical research to routine clinical application.