Does FLASH deplete Oxygen? Experimental Evaluation for Photons, Protons and Carbon Ions

TL;DR

This study experimentally evaluates oxygen depletion during FLASH irradiation with photons, protons, and carbon ions, finding that oxygen consumption depends on dose and dose rate but does not lead to total depletion at clinical doses.

Contribution

First experimental measurement of oxygen consumption across different radiation types during FLASH irradiation, revealing dose rate effects and the absence of total oxygen depletion.

Findings

Oxygen consumption depends on dose, dose rate, and LET.

Higher dose rates result in less oxygen consumption.

No total oxygen depletion occurs at clinical doses during FLASH.

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.