Ultra-rapid FLASH RT (sub-second dose delivery) has been shown to reduce detrimental effects of irradiation on normal tissues while still providing tumor control equivalent to conventional radiation therapy. The physical or biological mechanisms underlying this normal-tissue sparing as a function of dose at ultra-high dose rates is not fully understood. One of the major factors limiting both pre-clinical studies and clinical translation of FLASH RT is the difficulty in measuring FLASH irradiation beam parameters such as dose, dose per pulse, pulse repetition frequency, and time structure with the available conventional radiation detectors. The goal of this project is to develop a stand-alone FLASH detector system based on scintillator technology. Scintillator detectors’ fast response, dose-rate independence, dose linearity, and tissue equivalency make them well suited for FLASH beams. They also can provide real-time dose measurements with the required nanosecond-scale resolution for FLASH RT. The team will use Standard Imaging’s commercially available scintillator system as a starting point to develop a class of plastic scintillator detectors (PSDs) suited for FLASH beams. This project will yield a fully characterized scintillator detector system that is urgently needed to perform precise dose measurements of ultra-high dose rate beams, thereby enabling clinical use of FLASH RT.