Review on the VHEE Beam Energy Evolution for FLASH Radio Therapy with Ultra-High-Dose Rate (UHDR) Dosimetry

The very high energy electron (VHEE) beams, with energies ranging from 50 to 300 or to 400 MeV, are the subject of intense research investigation, drawing considerable interest in radiotherapy due to their accurate penetration into large and deeply seated tissue, sharp beam edges, high sparing properties, and low sensitivity to tissue density. The Very-High Energy Electron beam ranges from 50 to 400 MeV, and Ultra-High Energy Electron even to 1-2 GeV beams 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 the USA, Europe, Japan, and other countries. Those 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: developing compact, stable, and efficient accelerators, defining sophisticated treatment planning, and establishing clinically validated protocols. In addition, the perspective of VHEE to access ultra-high dose–rate (UHDR) dosimetry regime presents a promising procedure for the practical integration of FLASH radiotherapy of deep tumors, enhancing normal tissue sparing while maintaining the inherent dosimetric advantages. In this paper, we explore the technological progress and the electron accelerator beam energy technology evolution getting via the ASTRA code simulation results for the VHEE and UHEE beam development provided to medical applications.