Figure 9:

Dependence of the relative biological effectiveness (RBE) values on the threshold number of cells per colony as a criterion to distinguish between clonogenic and abortive colonies. Presented are the RBE values calculated using the criteria of 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100 cells/colony (these numbers shown in the upper right in each panel). The surviving fraction calculated with the Monte Carlo method was fitted to the equation y = exp (− ax), where a, x, y are slope, dose and surviving fraction, respectively, and R² denotes the correlation coefficient squared. Solid lines with solid circles indicate the surviving fraction for γ-rays, and dotted lines with open circles indicate the surviving fraction for carbon ions. The 10% survival dose was calculated as [ln (1/0.1)]/a, and the RBE was calculated based on the 10% survival dose.