RBE for carbon track-segment irradiation in cell lines of differing repair capacity.

PURPOSE The LET position of the RBE maximum and its dependence on the cellular repair capacity was determined for carbon ions. Hamster cell lines of differing repair capacity were irradiated with monoenergetic carbon ions. RBE values for cell inactivation at different survival levels were determined and the differences in the RBE-LET patterns were compared with the individual sensitivity to photon irradiation of the different cell lines. MATERIAL AND METHODS Three hamster cell lines, the wild-type cell lines V79 and CHO-K1 and the radiosensitive CHO mutant xrs5, were irradiated with carbon ions of different energies (2.4-266.4 MeV/u) and LET values (13.7-482.7 keV/microm) and inactivation data were measured in comparison to 250 kV x-rays. RESULTS For the repair-proficient cell lines a RBE maximum was found at LET values between 150 and 200 keV/microm. For the repair-deficient cell line the RBE failed to show a maximum and decreased continuously for LET values above 100 keV/microm. CONCLUSIONS The carbon RBE LET relationship for inactivation is shifted to higher LET values compared with protons and alpha-particles. RBE correlated with the repair capacity of the cells.

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