A radiation transport code based on a Monte Carlo tool is used to simulate a proton
therapy beamline designed to treat paediatric patients with intracranial tumours. The
treatments are performed using the IBA gantry at the Proton Therapy Centre of the Institut
Curie. The treatment is undertaken at 178.16 MeV using the double scattering technique.
The aim of this study is to present the Monte Carlo model of the transported proton beam,
beamline and treatment room, as well as the experimental validation of the proton dose
distributions calculated by this model. The beamline components and the treatment room are
accurately modelled using the Monte Carlo code MCNPX. The proton source at the beamline
entrance is defined on the basis of IBA data, measurements and calculations. Measured and
calculated relative proton dose distributions in a water phantom are compared for the
validation. Depth dose profiles, including pristine Bragg peaks and a spread–out Bragg
peak, and lateral dose profiles are studied. A general good agreement was found between
calculated and measured distributions with discrepancies of less than 2 mm. Relative
proton dose distributions are therefore considered to be correctly described by our
simulated geometry and proton source parameters. The Monte Carlo simulation will be used
subsequently for radiation protection purposes: calculation of secondary neutron doses
received by treated patients of different ages.