Background: Lymphocyte-dicentric assay is the most generally accepted method for biological dosimetry of overexposed individuals. In this study, the frequency of unstable chromosome
aberration in blood lymphocytes was used to estimate radiation dose received by individuals. Evaluation of dose using a calibration curve produced elsewhere may have a significant uncertainty; therefore, experiments were performed to produce a dose-response curve using an
established protocol of international atomic energy agency.

Materials and Methods: Lymphocytes in whole peripheral blood obtained from healthy
individuals, were exposed to various doses of gamma radiation (0.25 – 4 Gy). Then after 1 hour of incubation in 37 ^oC, were cultured in complete RPMI-1640 medium. 500 mitoses were
analysed for the presence or absence of unstable chromosomal aberrations for each radiation dose after the standard metaphase preparation and staining slides.

Results and Conclusion: Intercellular distribution of dicentric chromosomes at each radiation dose has been used to contrast a dose-response curve. It seems that dose-effect relationship
follows with the linear-quadratic model. There is a good agreement between our dose-response curves with similar published studies by other laboratories. Iran . J. Radiat. Res., 2004; 2 (2): 85-8 8