Figure 4. Average radial doses which are deposited following a single ionising event from 40 keV primary radiation in gold nanoparticles of a variety of sizes.

These doses are calculated by scoring the energy deposited to the water volume in concentric shells around the nanoparticle, and dividing these values by the mass of the water shell. Two features are particularly striking - firstly, areas in the vicinity of the nanoparticle (< 50 nm) see extremely large doses following a typical ionising event. Secondly, small nanoparticles deposit more dose in their local area than larger ones, due to the greater relative contribution from the outer layer of the nanoparticle. The scale and distribution of these doses are broadly similar to those seen in charged particle therapies in the vicinity of a track, which suggests the possible applicability of the local effect model as a way to analyse these results.