Low Dose Responses of Bone Marrow to X-Rays In Vivo

Radiation risk at low doses is determined by linear extrapolation from high dose epidemiological data. In the last decade many non-targeted effects have been reported which may be relevant to low dose risk determination. To investigate cell responses at such low doses we used bone marrow cells of mice. We have not observed non-targeted effects long- or short-term post irradiation. Exposure below 50-100 mGy provides no evidence of a dose response for apoptotic signaling, bystander effects and low responses for p53 and p21 induction with significant individual variability. There is also no evidence for long-term chromosomal instability in the bone marrow at doses below 1 Gy. The data also demonstrate unexpected thresholds above which dose-dependent damage signaling is observed and the chromosomal instability phenotype is induced. The data are consistent with low dose X-irradiation being less damaging than would be expected from the LNT paradigm.