Dose calculations with TRAX

The traditional microdosimetric approach uses observables such as the distribution of lineal energy deposition, y, and the specific energy deposition, z, to describe radiation quality with respect to damage in biological systems. A problem is, however, that there is no obvious link from purely physical observables to resulting biological effect. In recent developments, however, microdosimetric quantities have been used to predict biological damage with some success [3]. Hence there is a renewed interest in yand z-distributions, which can be measured in gas at low pressure and readily simulated with elementary interaction codes. Figure 1 shows experimental results for the doseweighted average of y, yD(b), as a function of distance, b, from the ion path in comparison with TRAX calculations. The strange shape of yD(b) as the counter moves out of the beam is clearly reproduced, as well as the almost constant contribution from δ-electrons at large distances. The higher energetic proton example shows significant discrepancies, which are not yet understood.