Threshold-type dose response for induction of neoplastic transformation by 1 GeV/nucleon iron ions.

Neoplastic transformation of HeLa X skin fibroblast human hybrid cells by doses of 1 GeV/nucleon iron ions in the range 1 cGy to 1 Gy to exposed cultures has been examined. The data indicate a threshold-type dose-response curve with no increase in transformation frequency until doses above 20 cGy. At doses <10 cGy, not all exposed cells receive a direct traversal of an iron-ion track core, but all exposed cells receive up to several mGy of low-LET radiation associated with the delta-ray penumbra. It is proposed that the threshold-type response seen is a consequence of an adaptive response associated with the delta-ray exposure. For comparison purposes, the dose response for Cs-137 gamma rays over the same dose range was examined using the same experimental procedure. As we have shown previously, the dose response for Cs-137 gamma radiation was J-shaped. The iron ions were 1.5 to 1.7 times more biologically effective than the gamma radiation over the dose range examined. (C) 2009 by Radiation Research Society