Relative Biological Effectiveness for Protons of Energies up to 31 MeV

The relative biological effectiveness (RBE) was determined for proton beams of 31, 12, and 8 MeV produced at the Milano University Cyclotron. Survival curves for human cells grown in monolayer at different proton energies and for γ rays from60 Co were determined. The minimum clone size to be chosen for definition of true survivors was examined. RBE values of 1.0 ± 0.1, 1.4 ± 0.2, and 1.5 ± 0.2, respectively, were found and compared with the results of other experiments in this energy range.