An investigation of the possibilities of BNCT treatment planning with the Monte Carlo method.

: The neutron fluence distribution inside two types of water phantom have been calculated with the Monte Carlo programme MCNP for the epithermal neutron beam at the Petten Low Flux Reactor. Comparison between the calculated and the measured neutron fluence distributions showed a reasonable agreement. The influence of beam and phantom geometry on the neutron fluence distribution has been calculated. An increase of the field size leads to a somewhat deeper position of the maximum of the thermal neutron fluence distribution in the cylindrical phantom. The possible use of beam modifying devices like wedges and blocks has been tested with this model. Blocks have been modelled that can locally reduce the fast neutron skin dose by 70%.