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/microm] is the track-average LET (linear energy transfer) in cells, and L1 [keV/microm] 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 500 keV/microm. L1 approximately 150 keV/microm was found to give the best fit and the sensitive area of the cell nucleus was determined as approximately 50 microm2 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 = approximately 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.