Effect of X-Ray Energy on the Quantitative Yield of γH2AX and 53BP1 Foci in Human Mesenchymal Stem Cells.

We compared the influence of X-rays generated at the peak anode voltages of 50, 100, and 200 kVp on the quantitative yield of foci (localized dynamic microclusters) of proteins involved in repair critical radiation-induced DNA damage, double-strand breaks (γH2AX and 53BP1), in cultured human mesenchymal stem stromal cells. Calculations of the relative biological effectiveness (RBE) based on the experimentally obtained dose curves of changes in the number of γH2AX and 53BP1 foci indicate that relative to the standard 200 kVp X-ray radiation taken as 1, the RBE of 100 kVp radiation is ~1.15, and that of 50 kVp is ~1.50. The obtained results indicate the necessity for thorough fundamental studies for evaluation of the real RBE of low-energy X-rays with subsequent correction of the weighting factor values.