PARENT SESSION
9:00 AM to 11:00 AM
Sunday, April 21, 2002
Symposium 5
Biologic Responses to Low Doses of Low LET Ionizing Radiation
Room: Nevada 6-7
Chair: Redpath, Les²²Department of Radiation Oncology, Irvine, CA, Co-Chair: Amundson, Sally³³National Institutes of Health, Bethesda, MD
Speakers: Amundson, Sally⁴; Boothman, David⁵; Joiner, Michael⁶; Redpath, Les⁷; Mitchel, Ronald⁸⁴National Institutes of Health, Bethesda, MD⁵Departments of Radiation Oncology and Pharmacology, Cleveland, OH⁶Dept of Radiation Biology, Detroit, MI⁷Department of Radiation Oncology, Irvine, CA⁸Department of Radiation Biology and Health Physics, Chalk River, ON

(S05-3) The shape of the dose response curve for radiation-induced neoplastic transformation at low doses.

Redpath, Les^*,1, Taylor, Thomas², Christie, Catherine², Elmore, Gene¹, ¹ Department of Radiation Oncology, Irvine, CA² Division of Epidemiology, Irvine, CA

ABSTRACT-
The dose-response curve for gamma-radiation-induced neoplastic transformation of HeLa x skin fibroblast human hybrid cells has been determined over the dose range 0.1 to 100 cGy. The results indicate that at doses up to 10 cGy the transformation frequencies are lower than the zero dose, spontaneous transformation frequency. It is concluded that this is a consequence of an adaptive response against spontaneous neoplastic transformation. Comparisons of the relative risks estimated from these in vitro data to those for cancer induction in exposed human populations reveal that they are remarkably similar. Experiments are currently underway with 60 kVp x-rays and preliminary results are also indicative of an adaptive response at low doses. Mechanistic aspects of these observations will be discussed. Supported by DOE Grant No. DE-FG07-99ER62876.

KEYWORDS: adaption, transformation, risk, radiation