The scoring of chromosomal aberrations in human lymphocytes provides the most sensitive method known for biological dosimetry. By scoring dicentrics in the full genome of 500 cells, average whole-body doses of about 0.1 Gy of X or γ rays may be detected and higher doses estimated. Acute doses above about 0.2 Gy can be estimated more accurately than similar chronic doses. For radiations of higher LET, for example those encountered in the space environment, the limits of detection in grays are lower. However, expressed in sieverts, the limits of detection are more nearly independent of radiation quality. This suggests for exposure to space radiations that it may be possible to convert the yield of aberrations directly to an average whole-body dose in sieverts, which can be used as an estimate of effective dose. The scoring of translocations involving about 20% of the genome in 1000 cells using fluorescence in situ hybridization painting techniques results in reduced sensitivity at low doses so that acute X-ray doses of about 0.3 Gy and chronic doses of about 0.4 Gy are at the limit of measurement. Better sensitivity can be achieved by scoring more cells or by using more chromosomes in color combinations, but a final limit to these approaches exists because of the higher level of spontaneous translocations than dicentrics in cells of unirradiated persons.

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