A MONTE CARLO TOOL FOR MULTI-TARGET NANODOSIMETRY.

A Monte Carlo simulation tool has been developed, based on the physical models of the Geant4-DNA extension of Geant4, to study the ionisation pattern of charged particles in a multi-target environment. The tool allows to code easily the geometry to build a simulation with multiple targets, since several parameters can be changed interactively and independently via macro commands. In this work a set of nanometric target spheres is embedded in a cylindrical water phantom 20 nm in height and 40 nm in diameter. The targets are randomly distributed in such a way that they do not overlap and are contained within a smaller cylindrical volume 20 nm in diameter and height. The water phantom is irradiated by ions which are shot parallel to the central axis and randomly distributed over the cross section of the inner cylinder. Two different types of simulations are performed. In one, the penumbra of secondary electrons is fully simulated, in the other the transport of secondary electrons is carried out only if they are produced inside one of the targets, and the electron track is terminated when it leaves the sphere of production. First results are presented and discussed.