Host: The Japan Radiation Research Society
Biological dose estimation in the radiological accident is considered to be very important as the first step in the medical treatment of persons exposed to radiation. The radiation dose is estimated by three methods; the clinical symptom, the count of the lymphocyte number and the analysis of chromosome aberrations peripheral blood lymphocytes (PBLs) of the exposed persons. Radiation induces many types (dicentric, translocation, ring etc.) of chromosome aberrations in the PBLs of the exposed individuals. Since dicentric chromosome is considered relatively radiation specific and the frequency of this aberration correlates with radiation dose , consequently, the dicentric chromosome is considered to be the most reliable, specific and sensitive biomarker for the dose estimation after acute and total radiation exposure. Therefore, this method is called as the "gold standard" for radiation biodosimetry. On the other hand, the analysis of chromosome translocation is used in the case of old exposure and chronic exposure because the lymphocytes with chromosome translocation remain for a long period after the radiation exposure. Furthermore, since the cells exposed to extremely high dose radiation will stop at G2 or earlier stage of the cell cycle and be dead due to apoptosis, the chromosomes are not identified in PBLs. However, in such cases, it is possible to analyze the chromosomes, in particular, ring chromosome, by using forcible condensation of DNA due to the treatment of chemical agents (PCC: premature chromosome condensation). This method is called the PCC-ring and used for the dose assessment in the case of higher radiation exposure. Also, in recent years, FISH techniques using DNA and PNA probe are applied to the dose estimation and will be discussed in this presentation.
