RELATIVE BIOLOGICAL EFFECTIVENESS OF CARBON IONS FOR LOCAL TUMOR CONTROL OF A RADIORESISTANT PROSTATE CARCINOMA IN THE RAT

Purpose: To study the relative biological effectiveness (RBE) of carbon ion beams relative to X-rays for local tumor control in a syngeneic rat prostate tumor (Dunning subline R3327-AT1). Methods and Materials: A total of 198 animals with tumors in the distal thigh were treated with increasing single and split doses of either C-12 ions or photons using a 20-mm spread-out Bragg peak. Endpoints of the study were local control (no tumor recurrence within 300 days) and volumetric changes after irradiation. The resulting values for D-50 (dose at 50% tumor control probability) were used to determine RBE values. Results: The D-50 values for single doses were 32.9 +/- 0.9 Gy for C-12 ions and 75.7 +/- 1.6 Gy for photons. The respective values for split doses were 38.0 +/- 2.3 Gy and 90.6 +/- 2.3 Gy. The corresponding RBE values were 2.30 +/- 0.08 for single and 2.38 +/- 0.16 for split doses. The most prominent side effects were dry and moist desquamation of the skin, which disappeared within weeks. Conclusion: The study confirmed the effectiveness of carbon ion therapy for severely radioresistant tumors. For 1- and 2-fraction photon and C-12 ion radiation, we have established individual D-50 values for local tumor control as well as related RBE values. (C) 2011 Elsevier Inc.