SENSITIVITY OF MICRONUCLEUS INDUCTION IN HUMAN-LYMPHOCYTES TO LOW-LETRADIATION QUALITIES - RBE AND CORRELATION OF RBE AND LET

To use the micronucleus (MN) assay as a biological dosimeter, it is es sential that the dose response to different radiation qualities is kno wn. In this paper we present dose-response curves for MN induction by X rays (14, 50 and 350 kVp) and Co-60 gamma rays. The dose responses f or 14 kVp compared to 50 kVp and for 350 kVp compared to Co-60 were fo und to differ significantly, whereas no significant difference could b e demonstrated between 50 kVp and 350 kVp. Calculated RBE values with respect to Co-60 gamma rays increase strongly with decreasing dose. Th e high RBE value (2.7) obtained for 14 kVp X rays in the low-dose regi on is of importance for radiological protection in clinical practice. A good linear correlation was found between the biological damage expr essed by the RBE values for MN induction and the calculated physical p arameter (LET) over bar(100,T) expressing the energy deposition patter n in the medium. This correlation points to the fact that secondary ph enomena involved in MN formation (repair, coagulation) do not differ g reatly 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 biol ogical dosimeter for radiation damage by X rays and gamma rays.