Abstract
Purpose: To investigate experimentally, if FLASH irradiation depletes oxygen
within water for different radiation types such as photons, protons and carbon
ions.
Methods: This study presents measurements of the oxygen consumption in
sealed, 3D printed water phantoms during irradiation with X-rays, protons and
carbon ions at varying dose rates up to 340 Gy/s. The oxygen measurement was
performed using an optical sensor allowing for non-invasive measurements.
Results: Oxygen consumption in water only depends on dose, dose rate and
linear energy transfer (LET) of the irradiation. The total amount of oxygen
depleted per 10 Gy was found to be 0.04 - 0.18 % atm for 225 kV photons, 0.04 -
0.25 % atm for 224 MeV protons and 0.09 - 0.17 % atm for carbon ions.
consumption depends on dose rate by an inverse power law and saturates for
higher dose rates because of self-interactions of radicals. Higher dose rates
yield lower oxygen consumption. No total depletion of oxygen was found for
clinical doses.
Conclusions: FLASH irradiation does consume oxygen, but not enough to deplete
all the oxygen present. For higher dose rates, less oxygen was consumed than at
standard radiotherapy dose rates. No total depletion was found for any of the
analyzed radiation types for 10 Gy dose delivery using FLASH.