Radiation Protection Dosimetry Advance Access originally published online on April 15, 2009
Radiation Protection Dosimetry 2009 134(1):55-61; doi:10.1093/rpd/ncp061
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Dicentric chromosomes and 
-H2AX foci formation in lymphocytes of human blood samples exposed to a CT scanner: a direct comparison of dose response relationships
1 Bayer Schering Pharma AG, 13342 Berlin, Germany
2 Institute of Radiation Biology, Helmholtz Zentrum München—German Research Center for Environmental Health, 85764 Neuherberg, Germany
3 Radiobiological Institute, University of Munich, 80336 München, Germany
* Corresponding author: Ernst.Schmid{at}lrz.uni-muenchen.de
Received October 30, 2008, amended February 24, 2009, accepted March 25, 2009
Experiments using the induction of dicentric chromosomes (dicentrics) as well as the 
-H2AX foci formation in lymphocytes of blood samples from a healthy donor were performed to directly evaluate the radiation sensitivity of both biological endpoints. For computed tomography scans at dose levels from 0.025 to 1 Gy, a linear-quadratic dose–response relationship for dicentrics and a linear dose–response relationship for -H2AX foci were obtained. The coefficients of the dose–response relationship for dicentrics are 
= (3.76 ± 0.29) x 10–2 Gy–1 and β = (5.54 ± 0.45) x 10–2 Gy–2, the linear coefficient for -H2AX foci is (7.38 ± 0.11) Gy–1. The findings indicate that scoring of dicentrics as well as microscopic analysis of -H2AX foci are sensitive methods to quantify a radiation-induced biological damage at low doses. However, since -H2AX foci can be partially repaired within a few hours, biological damages present for days or even months, which constitute the clinically relevant endpoints, can only be quantified reliably by scoring of chromosome aberrations. Thus currently the quantification of dicentrics or reciprocal translocations remains the recommended method for estimating the effect of exposures to low dose levels of radiation (‘biological dosimetry’). However, owing to the high radiation sensitivity of the -H2AX foci assay observed in the present study, further investigations on the effectiveness of low-linear energy transfer radiation qualities in producing -H2AX foci in lymphocytes from healthy donors should be performed.