Microdosimetry spectra and relative biological effectiveness of 15 and 30Â MeV proton beams

The relative biological effectiveness (RBE) of high-energy protons has been well investigated, but estimates of RBE for lower-energy (<40 MeV) protons are scarce. In the present work, measurements were made of the lineal energy spectra using a home-made miniature tissue-equivalent proportional counter for 15 and 30 MeV protons from the TR 30/15 cyclotron. Monte Carlo simulations were made for the same spectra using the FLUKA code. These spectra were coupled to several biological models to evaluate the RBE for various biological endpoints.