Fig. 1.

Schematic diagram of simulation geometry (not in scale) (a) For 150 kVp and 51 keV photon beams, the phase space were recorded for particles passing a 2 cm diameter area at 2 cm depth in a macroscopic water phantom. (b) The radiation field was reduced to the size of GNP and irradiated into GNP in vacuum. The outgoing electrons were scored in a second phase space file on the surface of GNP. (c) The second phase space was used as source in a microscopic water phantom.