Anti-tumor Effect of High Doses of Carbon Ions and X-Rays during Irradiation of Ehrlich Ascites Carcinoma Cells Ex Vivo

The effect of carbon ions (¹²C) with the energy of 400 MeV/nucleon on the dynamics of induction and growth rate of solid tumors in mice under irradiation of Ehrlich ascites carcinoma cells (EAC) ex vivo at doses of 5–30 Gy relative to the action of equally effective doses of X-ray radiation was studied. The dynamics of tumor induction under the action of ¹²C and X-rays had a similar character and depended on the dose during 3 months of observation. The value of the latent period, both when irradiating cells with ¹²C and X-ray, increased with increasing dose, and the interval for tumor induction decreased. The rate of tumor growth after ex vivo irradiation of EAC cells was independent of either dose or type of radiation. The dose at which EAC tumors are not induced within 90 days was 30 Gy for carbon ions and 60 Gy for X-rays. The value of the relative biological effectiveness of carbon ions, calculated from an equally effective dose of 50% probability of tumors, was 2.59.