Simulations of dose enhancement for heavy atom nanoparticles irradiated by protons.

A possible dose enhancement effect by proton or electron irradiation in the vicinity of nanoparticles consisting of different high Z atomic materials has been investigated using the track structure Monte Carlo code TRAX. In the simulations, Fe, Ag, Gd, Pt and Au nanoparticles (r = 22 and 2 nm) were irradiated with monoenergetic proton beams at energies of therapeutic interest (2, 80 and 300 MeV) and 44 keV electrons. Due to the large number of electrons in atoms with high atomic numbers, many electrons can be released in Auger cascades in addition to the primary ionization process. The potential additional nanoscopic radial dose contributions in the presence of metallic nanoparticles are assessed by comparison with liquid water and water simulated with the same density as the metallic materials. We find a noticeable impact of Auger electrons emitted from the nanoparticles. Special focus has been given to the assessment of complete sets of low-energy electron cross sections for the nanoparticle materials.

Advancing the modeling in particle therapy: from track structure to treatment planning.

We present a series of implementations on Monte Carlo track structure level which might have an impact on treatment planning for particle therapy. We evaluated the effect of multiple ion scattering and radical diffusion on the nanoscopic radial dose. Our cross section database for electron interactions was extended to be able to predict the sensitizing effect of gold nanoparticles in particle therapy. We also implemented LiF as a possible target for efficiency calculations of thermoluminescent detectors (TLDs).