Apoptosis induced by heavy ion (carbon) irradiation of two human tumours with different radiosensitivities in vivo: relative biological effectiveness (RBE) of carbon beam.

The effect of heavy ion (carbon beam) on apoptosis in vivo was studied. The human brain tumors xenografts of different radiosensitivities were used. The results demonstrated that the effect of carbon beam on apoptosis was similar to photon in radiosensitive tumors; however, carbon beam had the advantage on apoptosis in radioresistant tumors. In ependymoblastoma, a radiosensitive tumor, the incidence of apoptosis induced by photon and by carbon at 6 hours after irradiation were 34.5 +/- 7.85% and 32.5 +/- 7.04%, respectively. In glioblastoma (radioresistant tumor), the incidence of apoptosis induced by photon and by carbon at 6 hours after irradiation were 1.35 +/- 1.68% and 4.4 +/- 2.47%, respectively. Therefore, the incidence of apoptosis was increased more than 3-fold (RBE 3.0) at 6 hours after irradiation in glioblastoma. The heavy ion (carbon) beam is effective in radioresistant tumors in vivo.