Dose Rate Assessment of Spot-Scanning Very High Energy Electrons FLASH Radiotherapy Driven by Laser Plasma Acceleration

Abstract

This study assesses the dose rate delivered by the spot-scanning VHEE beams generated by laser plasma acceleration and discusses the feasibility and beam requirements for FLASH-RT. Different types of dose rate metrics (averaged-dose-rate (ADR), dose-averaged dose rate (DADR), and dose-threshold dose rate (DTDR)) in the spot-scanning situation are considered. Theoretical analysis and Monte Carlo simulations are performed to quantify the dose rate distribution for the water phantom and investigate the influence of beam parameters. All the beam parameters are derived from the experimental results. At a much lower pulse repetition rate of 5 Hz, ADR can only reach a dose rate at the magnitude of 10^-1 Gy/s, and the FLASH-RT dose rate (40 Gy/s) could be reached when the high-power laser's working repetition rate is kilo-Hertz. Different from ADR, DADR and DTDR are independent of the scanning path, and they can reach the ultra-high dose rate even exceeding 10^14 Gy/s. Meanwhile, the ultrashort electron bunch can be stretched during the scattering in the water, resulting in the dependence of DADR and DTDR on the penetration depth. DADR decreases exponentially from 10^14 Gy/s at the surface to 10^11 Gy/s at 15 cm depth. Both the charge per shot and angular spread are important parameters in the dose rate calculation. The distinct results among these 3 dose rate metrics are due to their correlations with the averaged beam current and instantaneous current. This study explored the practical beam parameters for preclinical use and provided guidance in designing LPA for the future spot-scanning VHEE FLASH-RT.