title: Density of hydroxyl radicals generated in an aqueous solution by irradiating carbon-ion beam.
abstract: The density of hydroxyl radicals (·OH) produced in aqueous samples by exposure to X-ray or carbon-ion beams was investigated. The generation of ·OH was detected by the electron paramagnetic resonance (EPR) spin-trapping technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping agent. When the concentration of DMPO is in excess of the generated ·OH, the production of DMPO-OH (spin-trapped ·OH) should be saturated. Reaction mixtures containing several concentrations (0.5-1685 mM) of DMPO were then irradiated by a 32 Gy 290 MeV carbon-ion beam (C290-beam) or X-ray. C290-beam irradiation was performed at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, National Institute of Radiological Sciences, Chiba, Japan), applying different linear energy transfers (LET) (20-169 keV/µm). The amount of DMPO-OH in the irradiated samples was detected by EPR spectroscopy. The generation of DMPO-OH increased with the concentration of initial DMPO, displayed a shoulder around 3.3 mM DMPO, and reached a plateau. This plateau suggests that the generated ·OH were completely trapped. Another linear increase in DMPO-OH measured in solutions with higher DMPO concentrations suggested very dense ·OH generation (>1.7 M). Generation of ·OH is expected to be localized on the track of the radiation beam, because the maximum concentration of measured DMPO-OH was 40 µM. These results suggested that both sparse (≈3.3 mM) and dense (>1.7 M) ·OH generation occurred in the irradiated samples. The percentage of dense ·OH generation increased with increasing LET. Different types of dense ·OH generation may be expected for X-ray and C290-beams.
authors.affiliation: Radio-Redox-Response Research Team, Advanced Particle Radiation Biology Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences.
authors.forename: Ken-ichiro
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Megumi
authors.initials: M
authors.lastname: Ueno
authors.forename: Ikuo
authors.initials: I
authors.lastname: Nakanishi
authors.forename: Kazunori
authors.initials: K
authors.lastname: Anzai
mesh_terms: D002244:Carbon / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry / Q000528:radiation effects; D063193:Heavy Ion Radiotherapy / Q000379:methods; D020450:Heavy Ions; D017665:Hydroxyl Radical / Q000737:chemistry* / Q000528:radiation effects*; D012996:Solutions; D014867:Water / Q000737:chemistry*; D014965:X-Rays
chemical_list: D005609:Free Radicals; D012996:Solutions; D014867:Water; D017665:Hydroxyl Radical; D002244:Carbon