Lethality of single-track events: comparison between calculations and experimental data.

Recent results on cell killing by microbeams were analysed using three parameters (k,L,L1), where k is the mean number of lethal particles per cell nucleus, L [keV/mu m] is the track-average LET (linear energy transfer) in cells, and L 1[keV/ mu m] is a critical value for inducing lethal damage by a single track. Analysis showed that calculations are consistent with two data sets. The existence of a quadratic dependence on LET of cellular effects is confirmed in the high-LET region between 30 and 500keV/ mu m. L1~150keV/mu m was found to give the best fit and the sensitive area of the cell nucleus was determined as ~50 mu m2 for Chinese hamster V79 cells. In microbeam experiments with several MeV alpha-particles, the relationship between k and L for V79 cells can be expressed as L ~150(k)-1/2. For a given survival level, the difference in the required dose (or L) between the microbeam and broad-beam experiments is also analytically described. [ABSTRACT FROM AUTHOR]