Microdosimetric investigations on collimated fast neutron beams for radiation therapy: II. The problem of radiation...

The correlation between radiation quality and cellular RBE of a mixed n-gamma field produced by a collimated fast-neutron beam produced by the bombardment of 14 MeV deuterons on Be in a water phantom is investigated. The microdosimetric parameters yF and YD are used for a physical description of the local distribution of radiation components. On the basis of the dose fractions of these components, the dependence of RBE on depth is calculated and is compared with experimental RBE data. Outside the beam centre, it is shown that the microdosimetric parameter y can be used for estimates of local changes of RBE, if particular conditions for the absorbed dose and for the range of neutron energies are met. The spatial distributions of y for the mixed radiation changes in RBE for equal absorbed doses of 1 Gy are at maximum 10% and thus perhaps negligible.