Cellular Recovery in Two Sub-lines of the L5178Y Murine Leukaemic Lymphoblast Cell Line Differing in Their Sensitivity to Ionizing Radiation

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Abstract
Cellular recovery was assessed in two sublines of L5178Y murine lymphoma cells of differing radiosensitivity (LY-S and LY-A4) using low dose-rate irradiation and split-dose experiments. No increase in cell survival was observed in the LY-S cell line until the dose-rate was reduced to 2 cGy/min, whereas in the LY-A4 cell line 20 cGy/min was low enough to detect changes in survival. The extent of this change, as assessed by dose reduction factors at 2 logs of cell kill, was greater in the LY-A4 cell line. Fitting these data with the incomplete repair model of Thames led to anomalous values for the half-time of repair. In split-dose experiments the maximum observed recovery ratio increased as a function of dose in a manner that is consistent with the linear-quadratic equation. As was found previously with radiosensitive human tumour cells, the LY-S cell line showed more split-dose recovery at any given dose than the LY-A4 cell line.