Is there reliable experimental evidence for a low-dose RBE of about 4 for mammography X rays relative to 200 kV X rays?
recently reported, on the basis of observations of neoplastic transformation in human hybrid CGL1 cells, a low-dose relative biological effectiveness (RBE(M)) of 4.3 for mammography X rays (29 kV) relative to 200 kV X rays. With reference to data in the literature, they inferred a factor of about 8 relative to 60Co gamma rays and concluded that this result is relevant to risk estimation. However, the conclusions do not appear to be valid. The data from the transformation study exhibit uncertainties in the statistical analysis that preclude any generalization of the inferred RBE(M). The data selected or inferred from the literature are likewise insufficient to support the stated RBEs. Our own uniform data set for the yields of dicentrics was obtained for widely varying photon energies with blood samples from the same donor, and it avoids interindividual variations in sensitivity as well as the differences in methodology that are associated with interlaboratory comparisons. Our data provide RBE(M) values for 29 kV X rays of 1.64 +/- 0.27 relative to 220 kV X rays and 4.75 +/- 1.67 and 6.12 +/- 2.51 relative to 60Co gamma rays.
Schmid
Ernst
E
GSF-National Research Center for Environment and Health, Institute of Radiobiology, Neuherberg, Germany. echmid@gsf.de
D002471:Cell Transformation, Neoplastic / Q000528:radiation effects; D002478:Cells, Cultured; D002869:Chromosome Aberrations; D002875:Chromosomes / Q000528:radiation effects; D003037:Cobalt Radioisotopes; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism / Q000528:radiation effects*; D008327:Mammography / Q000009:adverse effects*; D012062:Relative Biological Effectiveness; D015203:Reproducibility of Results; D014965:X-Rays
D003037:Cobalt Radioisotopes