The Shape of the Dose–Response Curve for Radiation-Induced Neoplastic TransformationIn Vitro: Evidence for an Adaptive Response against Neoplastic Transformation at Low Doses of Low-LET Radiation

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Abstract
Redpath, J. L., Liang, D., Taylor, T. H., Christie, C. and Elmore, E. The Shape of the Dose–Response Curve for Radiation-Induced Neoplastic Transformation In Vitro: Evidence for an Adaptive Response against Neoplastic Transformation at Low Doses of Low-LET Radiation. Radiat. Res. 156, 700–707 (2001).A dose–response curve for γ-radiation-induced neoplastic transformation of HeLa × skin fibroblast human hybrid cells over the dose range 0.1 cGy to 1 Gy is presented. In the experimental protocol used, the spontaneous (background) frequency of neoplastic transformation of sham-irradiated cultures was compared to that of cultures which had been irradiated with 137Cs γ radiation and either plated immediately or held for 24 h at 37°C prior to plating, for assay for neoplastic transformation. The pooled data from a minimum of three repeat large-scale experiments at each dose demonstrated a reduced transformation frequency for the irradiated compared to the sham-irradiated cells for doses of 0.1, 0.5, 1, 5 and 10 cGy for the delayed-plating arm. The probability of this happening by chance is given by 1/2n, where n is the number of observations (5); i.e., 1/32 ≅ 0.031. This is indicative of an adaptive response against spontaneous neoplastic transformation at least up to a dose of 10 cGy of γ radiation. The high-dose data obtained at 30 and 50 cGy and 1 Gy showed a good fit to a linear extrapolation through the sham-irradiated, zero-dose control. The delayed-plating data at 10 cGy and below showed a statistically significant divergence from this linear extrapolation.

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