Biological Dosimetry at the BfS

At the Federal Office for Radiation Protection (BfS) the national reference laboratory for biological dosimetry in Germany is located. Here dose estimations can be carried out on over-exposed or presumably over-exposed persons using biological indicators.

Method: chromosome aberration analysis in lymphocytes of peripheral blood

The method used is a chromosome aberration analysis in lymphocytes of peripheral blood. In many studies, the dicentric chromosome has proven to be the most reliable and sensitive biological indicator of exposure to ionising radiation. Because of its low spontaneous frequency, and because it is characteristic for ionising radiation, the dicentric chromosome is the most suitable indicator of a recent radiation exposure. The detection limit for homogenous whole-body exposure is 0.1 gray (Gy) for sparsely ionising radiation.

At the BfS, there are dose-effect curves for different radiation qualities established. From extensive investigations on healthy persons not exposed to radiation, there is a comprehensive control group available for the spontaneous frequency of various chromosome aberrations.

To prove acute radiation exposure, the frequency of dicentric chromosomes is routinely determined and a dose estimation is assessed using the calibration curves if a statistically secure (significant) increase of cytogenetic damage is ascertained in comparison to spontaneous frequency.

Reasons for chromosome analysis

Reasons for chromosome analysis include:

• radiation exposure or suspected radiation exposure when no physical dosimeter was carried,
• during monitoring it was estimated that the whole-body dose of 100 millisieverts (0.1 sievert) has been exceeded,
• discrepancies occured in the evaluation of physical radiation protection monitoring and an independent source of information is required,
• a presumed exposure dose is to be ruled out, for example when a dose has shown up on the dosimeter but the bearer of the dosimeter was not even exposed at all.

Dicentric chromosome (dic) with accompanying fragment (ace) in a human lymphocyte

The analysis process

Before a blood sample is taken, the BfS has to be contacted to discuss in advance the presumed radiation exposure and to ascertain whether a chromosome analysis for the purpose of dose estimation is feasible. If so, the Federal Office for Radiation Protection will send to the person or the attending physician a blood collection system together with a questionnaire which includes questions about the person and the circumstances of the accident.

After blood withdrawal and dispatch of the blood sample, employees in the laboratory prepare blood cultures. After two days, chromosome preparations are made from the lymphocytes of the blood cultures. Alternatively, micronuclei preparations can be performed after 3 days.

Subsequently, the structure and shape of the chromosomes are analysed or the micronuclei are recorded. Employees investigate how frequently dicentric chromosomes appear or determine the number of micronuclei. In case of an exposure dating back some time, they record the number of symmetrical translocations. Using the corresponding dose-effect curve, they estimate the dose, if there is a clearly noticeable (statistically significant) increase in chromosome damage.

Costs of chromosome analysis

Depending on time and effort needed for the respective analysis, chromosome analyses may be subject to charges. Remuneration for the service performed is invoked by contract. The federal states may make use of the service free of charge.