(a) Oxygen depletion g-values (μM/Gy) for
conventional and FLASH dose rates (black and red symbols, respectively), in
buffered aqueous solutions (5% BSA, 20 mM phosphate, pH 7.2) measured using
Oxyphor PtG4. The solid line represents a simulated g-value
dependence (see text and SI for details). (b) The tail of the oxygen depletion
trace for FLASH dose rate (105–109 Gy/s, 10 Gy per FLASH). Measurements
using Oxyphor PtG4 and PdG4 produced similar results. Experiments with Oxyphor
PdG4 are shown. Inset: depletion of oxygen upon application of FLASH (30 Gy, 100
Gy/s) is followed by a slow decay phase (time constant
t0~2 s). (c) g-Values in
the range of 30–140 μM for BSA solutions of different
concentrations (1%, 2% and 5%).