Biological Dosimetry

Abstract

Chromosome analysis is the method of choice in case of biological dosimetry, used for the quantification of exposures to ionising radiation. The advantages and disadvantages of dicentric chromosomes and symmetrical translocations are described. In general, confounding factors on the lower detectable dose limit and scoring criteria for symmetrical translocations are discussed. In the case of acute exposures, scoring of dicentric chromosomes is preferred when the blood sample can be taken shortly after the exposure. The dicentric chromosome is characteristic for ionising radiation and the spontaneous frequency is very low in the healthy general population (about one dicentric per 1,000 cells) and may be influenced by smoking. After whole-body exposure with low linear energy transfer radiation, doses down to about 100 mGy are detectable. In the case of chronic exposure or if the exposure happened years before blood sampling, the analysis of symmetrical translocations in stable cells is favoured. In contrast to dicentric chromosomes, which fade with time, symmetrical translocations can persist, being transmitted from bloodforming tissue to the peripheral blood. The background frequency of symmetrical translocations shows a clear age-dependency, resulting in an about tenfold higher spontaneous frequency and in higher individual variation. Using appropriate calibration curves, one can detect whole-body doses of about 300 mGy for individuals under 40 years of age and about 500 mGy for individuals over 40 years of age.