Figure 7.

Illustration of model predicted LQ parameters for proton and carbon ions. Model predicted survival curves for asynchronous hamster cells with low $\frac{\alpha }{\beta }$ ratio are shown in (a), for exposures to a range of LETs, including X-rays, protons (solid lines, LET < 30 keV) and carbon ions (dashed lines, LET > 30 keV). As is seen experimentally, survival curves become steeper with increasing LET, eventually becoming linear at very high LET. Model predicted LQ parameters are presented in (b and c). α can be seen to increase to a maximum and then fall, mimicking the trend in overall RBE, while β is relatively constant at low LET before falling as track numbers are reduced. Similar trends are presented in (d–f) for normal human cells, with a relatively high $\frac{\alpha }{\beta }$ ratio, showing that the trends are qualitatively similar across cells of different radiosensitivities.