ENERGY AND SPATIAL DEPENDENCE OF NEUTRON FLUXES IN RADIOTHERAPY ROOMS FOR A SIMPLE DOSE ESTIMATE METHOD

The analytical formulas found in a previous work for the spatial behaviour of the total photoneutron flux in a radiotherapy room have been applied to describe the fluxes in the various energy groups, by means of suitable coefficients resulting from fitting procedures on Monte Carlo simulation data. Copper and tungsten have been considered as the target constituting materials in the photoneutron source obtained from a 25 MV bremsstrahlung spectrum. The accelerator head shield has been simulated both with tungsten and lead. The knowledge of the spatial behaviour of the group fluxes allows the estimate of the dose equivalent per source neutron with a great accuracy.