Lethal, potentially lethal, and nonlethal damage induction by heavy ions in cultured human cells

In the fields of high-LET radiotherapy and space radiation safety it is important to know the relative probabilities with which a cell whose nucleus is struck by a heavy ion will be damaged or killed. Experiments were performed in which synchronous cultured human T-1 cells (presumptive HeLa) were irradiated with natural alpha particles of energy approximately 3.5 MeV at various times after mitotic selection up to the middle of S phase. Nuclear-area histograms were determined as a function of time after mitosis under conditions identical to those used for irradiation. The efficiency with which one particle passing through the nucleus killed a cell was found to be 0.14-0.20. This value was extrapolated to experimental cell survival data obtained when asynchronous cultured human cells were irradiated with He, Li, B, C, N, O, Ne, Ar ions of energy 6.58 or 5.5 MeV/amu, and the cell killing efficiency was found to be in the broad range of 0.5-1.0 under single-hit conditions. Similarly irradiated cells were examined for colony-size distribution by an image analysis technique, and it was found that the loss of large colonies was dose and LET-dependent in a systematic way. Dose-response data suggest two predominant subpopulations, resistant and sensitive cells, and it appears that the sensitive population is affected by single-hit kinetics. The single-hit coefficient for the induction of inherited slow growth varied with LET in a similar way to that for survival. The action cross section for this form of heritable damage appears to be comparable to the geometric cross section of the cell nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)