Radiobiological Effectiveness of Radiation Beams with Broad LET Spectra: Microdosimetric Analysis Using Biological Weighting Functions

Abstract

The evaluation of averaged parameters from microdosimetric spectra, measured with proportional counters and biological weighting functions of the quantity lineal energy, provides a practical solution to the specification of radiation quality, especially for radiations with broad LET spectra, such as those used for radiation therapy. This approach has already proved satisfactory for fast neutron therapy beams of different energy using a biological weighting function numerically determined on empirical and statistical bases using the results of a RBE-microdosimetry intercomparison study. The paper discusses the applicability of this procedure by extending the range of radiations to fast protons. For this purpose, the earlier neutron data were combined with preliminary results from RBE experiments and microdosimetric measurements performed within the framework of two proton therapy programmes. Different weighting functions were derived by unfolding calculations applied to data sets combining high energy gamma rays, fast neutrons and fast protons.