Intercomparison exercise on Monte Carlo simulations of electron spectra and energy depositions by a single gold nanoparticle under X-ray irradiation

Computational approaches, such as Monte Carlo (MC) radiation transport simulations, are used to estimate the dosimetric effects of GNPs, where results differing by orders of magnitudes have been reported by different investigators. This has motivated an intercomparison exercise, which was conducted as a joint activity of EURADOS Working Groups 6 "Computational Dosimetry" and 7 "Internal Dosimetry". The aim of this exercise was to determine the extent of such discrepancies between the results obtained by different researchers and different codes in a very simple simulation setup. Several individual EURADOS associate members and two code developer groups from outside Europe participated in this exercise applying seven different MC codes to perform the simulations of a simple defined geometry set-up of one single GNP irradiated in water by kilo-voltage X-rays. Two GNP diameters of 50 nm and 100 nm of were considered and two photon spectra as generated by X-ray tubes operated at 50 kV and 100 kV peak voltages. The geometry set-up and X-ray spectra were provided by the EURADOS task group. The participants were asked to determine for each combination of GNP size and X-ray spectrum the dose enhancement ratio (DER) of 10 nm-thick water shells up to 1000 nm and 1 μm-thick water shells up to 50 μm around the GNP. Furthermore, the electron spectra emitted from the GNP and the energy depositions in water shells around it were also to be reported. This EURADOS report summarizes the motivation and background for the exercise, the tasks to be solved, the codes used, the results reported by the participants, the consistency checks applied in their evaluation and a best estimates and uncertainty bands derived from the final results for the energy spectra of emitted electrons and the energy imparted in the vicinity of the GNP.