A quantitative analysis of carbon-ion beam-induced reactive oxygen species and redox reactions

The amounts of reactive oxygen species generated in aqueous samples by irradiation with X-ray or clinical carbon-ion beams were quantified. Hydroxyl radical ((OH)-O-center dot), hydrogen peroxide (H2O2), and the total amount of oxidation reactions, which occurred mainly because of (OH)-O-center dot and/or hydroperoxy radicals (HO2 center dot), were measured by electron paramagnetic resonance-based methods. (OH)-O-center dot generation was expected to be localized on the track/range of the carbon-ion beam/X-ray, and mM and M levels of (OH)-O-center dot generation were observed. Total (OH)-O-center dot generation levels were identical at the same dose irrespective of whether X-ray or carbon-ion beam irradiation was used, and were around 0.28-0.35 mu mol/L/Gy. However, sparse (OH)-O-center dot generation levels decreased with increasing linear energy transfer, and were 0.17, 0.15, and 0.09 mu mol/L/Gy for X-ray, 20 keV/mu m carbon-ion beam, and >100 keV/mu m carbon-ion beam sources, respectively. H2O2 generation was estimated as 0.26, 0.20, and 0.17 mu mol/L/Gy, for X-ray, 20 keV/mu m carbon-ion beam, and >100 keV/mu m carbon-ion beam sources, respectively, whereas the ratios of H2O2 generation per oxygen consumption were 0.63, 0.51, and 3.40, respectively. The amounts of total oxidation reactions were 2.74, 1.17, and 0.66 mu mol/L/Gy, respectively. The generation of reactive oxygen species was not uniform at the molecular level.