[RBE of carbon beam on hematopoietic injury]

The inactivation of hematopoiesis and survival of mice have been used in determining the relative biological effectiveness (RBE) of heavy charged particles of carbon 12 generated by Riken ring-cyclotron. Whole bodies of anesthetized mice were exposed to accelerator-generated carbon 12 of 135 MeV/u or X-rays of 200 kVp in graded doses. At about 5 hours after exposure, exogenous spleen colonies (CFU-S), granulocyte-macrophage progenitor cells (GM-CFC) and megakaryocyte progenitor cells (Meg-CFC) were assayed to determine dose relationships, and then D0 doses were determined. The inactivation of blood cells and lethality of mice (LD50/30) were also monitored for 30 days after irradiation. The RBE values of the 135 MeV/u carbon beam in terms of CFU-S were 1.68 for marrow and 1.41 for spleen, for GM-CFC they were 1.56 for marrow and 3.29 for spleen, for Meg-CFC they were 1.25 for marrow and 3.73 for spleen, while they were about 1.0 for erythrocytes, leukocytes and thrombocytes in mice irradiated with 2 Gy. However, the RBE values of the carbon beam were 1.32 for LD50/30.