Real-time optical oximetry during FLASH radiotherapy using a phosphorescent nanoprobe.

• Oxygen depletion during irradiation was measured dynamically using a nanoparticle. • Oxygen depletion yields was measured at 200 Hz using a fiber-optic system. • Ultra-high dose rate radiation depleted 13% less oxygen than conventional radiation. • Radiochemical oxygen depletion is lower under hypoxic conditions, i.e., below 20 µM. The rapid depletion of oxygen during irradiation at ultra-high dose rate calls for tissue oximeters capable of high temporal resolution. This study demonstrates a water-soluble phosphorescent nanoprobe and fiber-coupled instrument, which together are used to measure the kinetics of oxygen depletion at 200 Hz during irradiation of in vitro solutions. [ABSTRACT FROM AUTHOR]