Review of VHEE Beam Energy Evolution for FLASH Radiation Therapy Under Ultra-High Dose Rate (UHDR) Dosimetry

Very-high-energy electron (VHEE) beams, ranging from 50 to 300 or 400 MeV, are the subject of intense research investigation, with considerable interest concerning applications in radiation therapy due to their accurate energy deposition into large and deep-seated tissues, sharp beam edges, high sparing properties, and minimal radiation effects on normal tissues. The very-high-energy electron beam, which ranges from 50 to 400 MeV, and Ultra-High-Energy Electron beams up to 1–2 GeV, are considered extremely effective for human tumor therapy while avoiding the spatial requirements and cost of proton and heavy ion facilities. Many research laboratories have developed advanced testing infrastructures with VHEE beams in Europe, the USA, Japan, and other countries. These facilities aim to accelerate the transition to clinical application, following extensive simulations for beam transport that support preclinical trials and imminent clinical deployment. However, the clinical implementation of VHEE for FLASH radiation therapy requires advances in several areas, including the development of compact, stable, and efficient accelerators; the definition of sophisticated treatment plans; and the establishment of clinically validated protocols. In addition, the perspective of VHEE for accessing ultra-high dose rate (UHDR) dosimetry presents a promising procedure for the practical integration of FLASH radiotherapy for deep tumors, enhancing normal tissue sparing while maintaining the inherent dosimetry advantages. However, it has been proven that a strong effort is necessary to improve the main operational accelerator conditions, ensuring a stable beam over time and across space, as well as compact infrastructure to support the clinical implementation of VHEE for FLASH cancer treatment. VHEE-accessing ultra-high dose rate (UHDR) perspective dosimetry is integrated with FLASH radiotherapy and well-prepared cancer treatment tools that provide an advantage in modern oncology regimes. This study explores technological progress and the evolution of electron accelerator beam energy technology, as simulated by the ASTRA code, for developing VHEE and UHEE beams aimed at medical applications. FLUKA code simulations of electron beam provide dose distribution plots and the range for various energies inside the phantom of PMMA.