  A Geant4 based simulation platform of the Holland Proton Therapy Centre
(HollandPTC, Netherlands) R&D beamline (G4HPTC-R&D) was developed to enable the
planning, optimisation and advanced dosimetry for radiobiological studies. It
implemented a six parameter non-symmetrical Gaussian pencil beam surrogate
model to simulate the R&D beamline in both a pencil beam and passively
scattered field configuration. Three different experimental proton datasets (70
MeV, 150 MeV, and 240 MeV) of the pencil beam envelope evolution in free air
and depth-dose profiles in water were used to develop a set of individual
parameter surrogate functions to enable the modelling of the non-symmetrical
Gaussian pencil beam properties with only the ProBeam isochronous cyclotron
mean extraction proton energy as input. This refined beam model was then
benchmarked with respect to three independent experimental datasets of the R&D
beamline operating in both a pencil beam configuration at 120 and 200 MeV, and
passively scattered field configuration at 150 MeV. It was shown that the
G4HPTC-R&D simulation platform can reproduce the pencil beam envelope evolution
in free air and depth-dose profiles to within an accuracy on the order of
$\pm$5% for all tested energies, and that it was able to reproduce the 150 MeV
passively scattered field to the specifications need for clinical and
radiobiological applications.
