Radiation shielding and safety implications following linac conversion to an electron FLASH?RT unit

Purpose Due to their finite range, electrons are typically ignored when calculating shielding requirements in megavoltage energy linear accelerator vaults. However, the assumption that 16 MeV need not be considered does hold operated at FLASH-RT dose rates (~200× clinical rate), where rate from bremsstrahlung photons is an order of magnitude higher than 18 MV beam for which was designed. We investigate and radiation protection impact converting a Varian 21EX linac rates. Methods performed survey all occupied areas using Fluke Biomedical Inovision 451P meter Wide Energy Neutron Detection Instrument (Wendi)-2 FHT 762 neutron detector. The activated components following 1.8-min delivery also measured. Results When gantry angle 180° such as during biology experiments, deliver ~10 µSv/h controlled 780 uncontrolled areas, above 20 µSv any 1-h USNRC limit. exceed µSv, unit must continuously 92 s, corresponds this bunker 3180 Gy workload isocenter, would unfeasible within timeframe due experimental logistics. While steering dosimetry activities can require workloads magnitude, these activities, positioned 0° area becomes undetectable. Likewise, activation reach 25 near isocenter delivery, but dissipates minutes, total doses hour below µSv. Conclusion Bremsstrahlung created by electron resulted consequential vault. our vault proved sufficient, other investigators prudent confirm adequacy safety program, particularly if operating vaults designed 6 MV.