Fig. 1.

Survival curves of V79 cells irradiated with X-rays or with protons at different depths. Clonogenic survival of V79 cells irradiated with X-rays (white square, dashed line) or protons (closed circle, solid line) at each depth (A–F as shown in Table 1); surviving colonies were stained and counted after 7 days of incubation. Dose–response curves were fitted using linear–quadratic models as described in Materials and Methods, and RBE₁₀ and RBE₃₇ values were calculated from D₁₀ and the D₃₇ values. With regard to spatial resolution of dosimetry system, the dose error was <0.5%.