Free radical reaction and oxygen consumption in an aqueous solution by an X-ray irradiation

Introduction: High LET carbon ion beam cancer therapy at National Institute of Radiological Sciences (Chiba, Japan) began in 1994. Considering the expansion of heavy-ion cancer therapy, the quality and accuracy of the heavy-ion therapy must be improved and optimized. Detection of free radical reactions and geometry in a large sample irradiated by a heavy-ion beam is thus important to understand the effect of high LET irradiation in patients. Therefore, a new method to detect free radical generation, which can be translated to an imaging technique, is required. In this experiment, using an X-ray irradiation, the imaging-translational detection of H2O2 generation in an aqueous sample was tested. Method: LiPc crystal was put into a plastic microtube. The microtube was filled with mili-Q water or PBS, and sealed air-tightly without any bubble in the tube. The tube was irradiated by X-ray (Eeff = 80 keV) with dose of 256 Gy. After the irradiation, EPR spectra of LiPc in the tube were measured at L-band (1.2 GHz). The pO2 value in the tube was estimated from the linewidth of EPR spectrum of LiPc. A similar sample without LiPc was irradiated by X-ray (256 Gy), and then H2O2 concentration in the tube was measured. A water solution of TEMPOL (2 mM) was irradiated by X-ray (356 Gy), and the reduction of the EPR signal of TEMPOL was measured. Results and Discussion: By irradiating 256 Gy of X-ray, pO2 in the irradiated water was decreased by 30 mmHg, and generation of 60 mol/L H2O2 in the irradiated water was detected. When a water solution of TEMPOL (2 mM) was irradiated by 256 Gy of X-ray, EPR signal of TEMPOL in the sample was decreased. The H2O2 generated in the water during the irradiation can make the reduction of TEMPOL without hydrogen-donor, such as GSH, NADH, or NADPH. This experimental design will be translated to imaging experiment and applied to the high LET radiation such as heavy-ion beams in the future.Oxygen Club of California 2008 World Congres