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No abstract available

[en] In vitro dose-response curves are used to describe the relation between chromosome aberrations and radiation dose for human lymphocytes. The lymphocytes are exposed to low-LET radiation, and the resulting dicentric chromosome aberrations follow the Poisson distribution. The expected yield depends on both the magnitude and the temporal distribution of the dose. A general dose-response model that describes this relation has been presented by Kellerer and Rossi (1972, Current Topics on Radiation Research Quarterly 8, 85-158; 1978, Radiation Research 75, 471-488) using the theory of dual radiation action. Two special cases of practical interest are split-dose and continuous exposure experiments, and the resulting dose-time-response models are intrinsically nonlinear in the parameters. A general-purpose maximum likelihood estimation procedure is described, and estimation for the nonlinear models is illustrated with numerical examples from both experimental designs. Poisson regression analysis is used for estimation, hypothesis testing, and regression diagnostics. Results are discussed in the context of exposure assessment procedures for both acute and chronic human radiation exposure

[en] In vitro dose-response curves are used to describe the relation between the yield of dicentric chromosome aberrations and radiation dose for human lymphocytes. The dicentric yields follow the Poisson distribution, and the expected yield depends on both the magnitude and the temporal distribution of the dose for low LET radiation. A general dose-response model that describes this relation has been obtained by Kellerer and Rossi using the theory of dual radiation action. The yield of elementary lesions is kappa[γd + g(t, tau)d²], where t is the time and d is dose. The coefficient of the d² term is determined by the recovery function and the temporal mode of irradiation. Two special cases of practical interest are split-dose and continuous exposure experiments, and the resulting models are intrinsically nonlinear in the parameters. A general purpose maximum likelihood estimation procedure is described and illustrated with numerical examples from both experimental designs. Poisson regression analysis is used for estimation, hypothesis testing, and regression diagnostics. Results are discussed in the context of exposure assessment procedures for both acute and chronic human radiation exposure

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[en] Several authors have reported small, but statistically significant, increases in sister chromatid exchanges (SCEs) in mammalian cells exposed to low-LET radiation during culture in the presence of [³H]-thymidine or bromodeoxyuiridine (BUdR). To determine whether ionizing radiation also induces lesions in the unsubstituted DNA of G₀ lymphocytes that lead to SCEs in second division metaphases, we exposed human lymphocytes to 150 or 300 ⁶⁰Co-γ radiation prior to culture in the presence of phytohemagglutinin and BUdR. Increased frequencies of SCEs were not observed in the irradiated cultures, either in second division metaphases having ring and dicentric chromosomes or those that did not have detectable chromosome aberrations. these findings suggest that increased frequencies of SCEs would not be observed in cultured lymphocytes from persons with in vivo exposures to radiation, and raise questions regarding the efficacy of ionizing radiation in inducing long-lived lesions in native DNA that can subsequently be expressed as SCEs

[en] To provide dosimetry for radiation accident management, in vitro dose-response models are used for deriving biological estimates of the doses received by individuals involved in accidents. The dose estimates are made by comparing the frequency of specific cytogenetic aberrations in cultured blood lymphocytes of the exposed person with the frequency observed in human lymphocytes irradiated in vitro. Three factors influenced the accuracy of the in vitro dose-response relation determinations. These are the biological aspects of lymphocytes and the culture system, statistical and mathematical aspects of data collection and analysis, and the physical conditions of the in vitro radiation exposure. Each of these factors is discussed and examples of dose-response curves generated for needs of dose-determination in accidents involving americium 241 and iridium 192

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[en] The analysis of mitotic indices (MI) and chromosome breakages in metaphases of 50-hr lymphocyte cultures exposed to the calcium or zinc chelates of diethylenetriamine pentaacetic acid (DTPA) demonstrated: (1) an 80% reduction in MI in cultures from three women but no reduction in those from two men after in vitro exposure to CaDTPA in concentrations as low as 10μg/ml culture medium, and complete suppression of mitoses in cultures from men and women after exposure to 40 μg/ml CaDTPA; (2) minor suppression in MI in cultures from women and none in those from men after exposure to 40 or 80 μg/ml ZnDTPA; (3) no ring or dicentric chromosomes in 1700 metaphases from DTPA-treated cultures. Likewise, the authors observed no differences in the frequency or distributions of rings and dicentrics in lymphocyte cultures from two persons after in vitro exposure to 250-R ⁶⁰Co γ radiation in the presence or absence of 10 μg/ml CaDTPA or 10 or 80 μg/ml ZnDTPA

[en] Cytogenetic dosimetry estimates to guide treatment of persons internally contaminated with transuranic elements have not previously been possible because appropriate in vitro dose-response curves specifically for alpha particle irradiation of human lymphocytes do not exist. Using well-controlled cytogenetic methods for human lymphocyte culture, an experimentally derived dose-response curve for ²⁴¹Am alpha particle (5.49 and 5.44 MeV) radiation of G₀ lymphocytes was generated. Cells were exposed to 43.8, 87.7, 175.3 or 350.6 nCi/ml ²⁴¹Am for 1.7 hr giving doses of 0.85, 1.71, 3.42 or 6.84 rad. Based on dicentric chromosome yield, the linear dose-response equation is Y = 4.90(+-0.42) x 10^-2 X, with Y given as dicentrics per cell and X as dose in rads. The study also shows that the two-break asymmetrical exchanges in cells damaged by alpha particle radiation are overdispersed when compared to a Poisson distribution. An example is presented to show how the derived dose-response equation can be used to estimate the radiation dose for a person internally contaminated with an actinide. An experimentally derived RBE value of 118 at 0.85 rad is calculated for the efficiency of ²⁴¹Am alpha particle induction of dicentric chromosomes in human G₀ lymphocytes as compared with the efficiency of ⁶⁰Co gamma radiation. The maximum theoretical value for the RBE for cytogenetic damage from alpha irradiation was determined to be 278 at 0.1 rad or less which is in marked contrast to previously reported RBE values of approx. 20. (author)