Establishment and validation of surface model for biodosimetry based on gamma-H2AX foci detection

Introduction: In the event of a radiation accident detecting gamma-H2AX foci is being accepted as fast method for triage and dose assessment. However, due to their disappearance kinetics, published calibrations have been constructed at specific post-irradiation times. Objectives: To develop a surface, or tridimensional, model to estimate doses at times not included in the calibration analysis, and to validate it. Materials and methods: Calibration data was obtained irradiating peripheral mononucleated cells from one donor with radiation doses ranging from 0 to 3 Gy, and gamma-H2AX foci were detected microscopically using a semi-automatic method, at different post-irradiation times from 0.5 to 24 h. For validation, in addition to the above-mentioned donor, blood samples from another donor were also used. Validation was done within the range of doses and post-irradiation times used in the calibration. Results: The calibration data clearly shows that at each analyzed time, the gamma-H2AX foci frequency increases as dose increases, and for each dose this frequency decreases with post-irradiation time. The gamma-H2AX foci nucleus distribution was clearly overdispersed, for this reason to obtain bidimensional and tridimensional dose-effect relationships no probability distribution was assumed, and linear and non-linear least squares weighted regression was used. In the two validation exercises for most evaluated samples, the 95% confidence limits of the estimated dose were between +/- 0.5 Gy of the real dose. No major differences were observed between donors. Conclusion: In case of a suspected overexposure to radiation, the surface model here presented allows a correct dose estimation using gamma-H2AX foci as biomarker. The advantage of this surface model is that it can be used at any post-irradiation time, in our model between 0.5 and 24 h.