A–7.
Dicentric chromosomes are almost exclusively induced by ionizing radiation. The spontaneous frequency of dicentrics is very low in the healthy general population (about 1 dicentric per 1000 cells). Dicentric frequencies in peripheral blood lymphocytes can show a clear linear quadratic dose–effect relationship up to around 5 Gy for acute photon exposures. Owing to these characteristics, the dicentric assay is able to detect whole body doses down to about 0.1 Gy from the analysis of 500–1000 metaphase spreads. Ideally, the dicentric assay is performed on blood samples within a few days of the exposure.
A–8.
The duration of this assay depends on the number of cells analysed, on the level of automation and on the experience of the personnel. An assay takes 3 d or longer, including at least 51 h for sample preparation. Dose estimates based on an analysis of 20–50 cells (1–2.5 h) are sufficient for estimating the order of magnitude of the exposure, even if with large uncertainties (±0.5 Gy). Mathematical procedures are available to take partial body exposure or dose protraction into account [A–2, A–3].