Distribution of Hydrogen Peroxide-dependent Reaction in a Gelatin Sample Irradiated by Carbon Ion Beam

摘要

We investigated the amount and distribution of hydrogen peroxide (H₂O₂) generated in a solid gelatin sample irradiated by heavy ion (carbon) beam. We irradiated the gelatin sample, which contained a nitroxyl radical (4-hydroxy-2,2,6,6-tetramethylpiperidine- N -oxyl, TEMPOL), with a 290-MeVucleon carbon beam (~128 Gy). To verify the distribution of H₂O₂ generation in the irradiated sample, we employed both electron paramagnetic resonance (EPR) spectroscopic and magnetic resonance (MR) imaging methods based on H₂O₂-dependent paramagnetic loss of TEMPOL. We obtained a distribution profile of the H₂O₂-dependent reaction in the gelatin sample when we irradiated gelatin samples with carbon beams with several different linear energy transfer (LET) values. Because the profiles of oxygen consumption in the gelatin sample measured by L-band EPR oxymetry and of the H₂O₂-dependent reaction have almost the same shape, the profile of the H₂O₂-dependent reaction can be used as an estimation of the profile of the generation of H₂O₂. The H₂O₂ profile in one intact gelatin sample scanned by 7-tesla MR imaging showed a similar shape as a result of the EPR experiment. We obtained several hundreds of micromolars of H₂O₂ generated in a gelatin sample irradiated by carbon beam when 200 Gy was given at the surface of the sample. H₂O₂ distribution was almost flat, with only a slight peak just before the end of the beam.