Sensitivity of Micronucleus Induction in Human Lymphocytes to Low-LET Radiation Qualities: RBE and Correlation of RBE and LET

To use the micronucleus (MN) assay as a biological dosimeter, it is essential that the dose response to different radiation qualities is known. In this paper we present dose-response curves for MN induction by X rays (14, 50 and 350 kVp) and⁶⁰ Co γ rays. The dose responses for 14 kVp compared to 50 kVp and for 350 kVp compared to⁶⁰ Co were found to differ significantly, whereas no significant difference could be demonstrated between 50 kVp and 350 kVp. Calculated RBE values with respect to⁶⁰ Co γ rays increase strongly with decreasing dose. The high RBE value (2.7) obtained for 14 kVp X rays in the low-dose region is of importance for radiological protection in clinical practice. A good linear correlation was found between the biological damage expressed by the RBE values for MN induction and the calculated physical parameter$\overline{{\rm LET}}_{100,{\rm T}}$ expressing the energy deposition pattern in the medium. This correlation points to the fact that secondary phenomena involved in MN formation (repair, coagulation) do not differ greatly for the X-ray qualities used in this work. It can be concluded that MN induction in human lymphocytes can be used as a sensitive biological dosimeter for radiation damage by X rays and γ rays.