Presentation Quantification of Reactive Oxygen Species Induced by Carbon Ion Beam

Ken-ichiro, Matsumoto

Amounts and nano-distributions of reactive oxygen species (ROS) generated by carbon beam (C-beam) were assessed using electron paramagnetic resonance (EPR) based methods and then compared to that of X-ray. Hydroxyl radical (•OH) can be generated by radiolysis of water in the very early phase of the radiation. Sequentially, superoxide (O2•-) and hydrogen peroxide (H2O2) were generated with or without oxygen (O2) consumption. Hydroperoxyl radical (HO2•), which is equilibrated with O2•- in aqueous atmosphere, is the other form of O2•- and a relatively strong oxidant. Relation between the radiation quality and the generations of ROS was discussed.Total oxidation reactions, which is mainly caused by •OH and HO2•, were measured by EPR redox probing method using TEMPOL as the redox probe. H2O2 generations were measured by another EPR redox probing methods also using TEMPOL as the redox probe. The O2 consumptions were measured by EPR oximetry using LiNc-BuO as the oxygen probe. The •OH generations and its nano-distributions were quantified by EPR spin trapping method using DMPO as the spin trapping agent.Total oxidations were estimated as 3, 1.3, and 0.66 μmol/L/Gy for X-ray, 20 keV/μm C-beam, and 80 keV/μm C-beam, respectively. Amount of H2O2 generation was estimated as 0.2, 0.57, and 0.35 μmol/L/Gy. The total oxidations and H2O2 decreased with increasing LET when an identical dose was given. The oxygen consumptions were also decreased with increasing LET, and were 0.4, 0.39, and 0.15 μmol/L/Gy for X-ray, 20 keV/μm C-beam, and 80 keV/μm C-beam, respectively. However, the ratio of H2O2 generation per oxygen consumption were increased with LET, and were 0.5, 1.46, 2.33 for X-ray, 20 keV/μm C-beam, and 80 keV/μm C-beam, respectively. The •OH generations expected to be localized on the track/range of the radiation beam/ray. The results suggested both sparse (≈ 3.3 mM) and very dense (> 1.7 M) •OH generation in the irradiated samples. Different types of dense •OH generation, i.e. dens •OH clusters scattered in X-ray region and very dense •OH localized on a straight truck of carbon ion beam, were expected. Percentage of dense •OH generation increased with LET becoming higher. The character of ROS generations can give the radiation quality.
2nd Symposium of the Medical Particle Beam Research Group

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