Biological dosimetry refers to the use of tests of biological matter to determine the dose it was exposed to. It is especially useful in radiation accidents when physical dosimetry (eg. TLD or ionisation chamber) is not possible.
Clinical dosimetry utilises symptoms or signs to estimate the absorbed dose. For acute radiation sickness, vomiting is the best indication. Onset of vomiting after two hours suggests a dose between 1 – 2 Gy. Vomiting between 1-2 hours suggests 2-4 Gy, between 30 minutes and 1 hour indicates 4 – 6 Gy and within 30 minutes indicates that a dose over 6 Gy was received to the whole body.
Lymphocytes and granulocytes in the peripheral blood decrease in number relative to the total body dose received. Lymphocytes typically respond rapidly, and their level after two days predicts the severity of radiation injury (from none to lethal). Neutrophils respond more slowly, with the nadir occurring approximately 20 – 30 days following exposure.
The mitotic index is the number of cells actively undergoing mitosis versus those in interphase. It is possible to either count the number of cells in mitosis on a glass slide, or use other methods to separate the two populations – mitotic cells are typically less attached to their neighbours and are removed more easily from a cell suspension.
Radiation may induce interphase arrest, leading to a decreased mitotic index. This method can be used to analyse cell cultures following radiation delivery.
Chromosomal Abberations in Peripheral Lymphocytes
Lymphocytes can be harvested in large numbers from the peripheral bloodstream. Most of these lymphocytes are resting (G0) but can be induced to begin division by the administration of phytohaemagglutinin (PHA). If division is paused at mitosis (eg. with colchicine) then the choromsomes may be viewed and abberatiosn visualised. The most common abberations are due to double strand breaks, and include translocation, dicentric breaks, inversion or an accentric ring formation.