High-LET-induced chromosome aberrations in V79 cells analysed in first andsecond post-irradiation metaphases

Purpose: As an extension of previous studies, the time-course of high-LET-i nduced chromosomal damage was investigated in first- and second-cycle V79 C hinese hamster cells. Materials and methods: Cells were exposed in G(1) to 10.4MeV/u Ar ions (LET =1226keV/mu m) and chromosomal damage was measured at 2 h sampling interval s between 10h and 34 h after irradiation. To distinguish between cells in d ifferent postirradiation cycles, the fluorescence-plus-Giemsa technique was applied. Results: For first- and second-generation cells, the number of aberrant met aphases and aberrations per metaphase were found to increase markedly with sampling time, demonstrating that cell cycle progression was delayed accord ing to the number of lesions carried by the cell. To account for the time-d ependent expression of chromosomal damage a mathematical approach was used based on the integrated flux of aberrant cells entering mitosis. Moreover, the analysis of Ar ion-induced chromosome lesions confirmed that high-LET r adiation results in specific changes in the spectrum of aberration types. I n particular, an increased rate of chromatid-type aberrations as well as a high frequency of chromosomal breaks was found, although the cells were exp osed in G(1). Conclusions: Due to the fact that cells collected at one sampling time are not representative of the entire population, the complete time-course of ch romosomal damage has to be taken into account for the determination of a me aningful RBE value. Otherwise, the analysis of chromosomal damage can resul t in a pronounced over- or underestimation of the RBE depending on the subp opulation of cells entering mitosis at that particular sampling time.