Objectives: Intrinsic radiosensitivity at doses used in radiotherapy is linked to hypersensitivity (HRS) and increased radio resistance (IRR) at low doses. The aim of this study was to explore this relationship. Methods: Survival curves for 18 human tumour cell lines were analysed, using two models to fit the data points in order to extract the necessary parameters relevant for this study. Results: The IRR ratio α s /α r versus the survival at 2 gray (Gy) can be described by a logarithmic relation which leads to a series of straight lines. Conclusion: The relationship obtained implies that there is a direct link between HRS/IRR and survival at clinically relevant doses of 2 Gy. Keywords

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In order to study the hypersensitivity phenomena in single strand cells, E-Coli bacteria cultures were irradiated by alpha particles emitted from Am 241 point source. The cells showed hypersensitivity at 0.05 Gy. Survival curves models were fitted to the data. The recent hypersensitivity models fitted the data much better than the old conventional models.