Microdosimetric measurements in the fast neutron therapeutic beam of Nice

Fast neutrons are used with success in some cancer pathologies. However actual therapeutic plans do not take into account that fast neutron beams change their physical quality and biological quality with depth in tissue. In this paper we have measured the physical quality, and its variation with the depth, of the fast neutron therapeutic beam of the centre Antoine-Lacassagne of Nice (France). The results have been compared with some radiobiological data and with some measurements of other similar therapeutic beams. The physical quality has been measured by using microdosimetric techniques. Measurements have been performed with the 1/2" LET proportional counter of the Far West Technology Inc at simulated diameter of 2 mu m. Experimental data confirm a decreasing of the neutron beam quality with depth together with an increase of the gamma component. Microdosimetric data of Nice neutron beam are consistent with those of other similar therapeutic beams