246 research outputs found

    Dose Estimation by Chromosome Analysis

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    Chromosomal aberrations in the peripheral lymphocytes are the most reliable biological indicator for estimating the dose in radiation exposures. Peripheral lymphocytes are in the G0 phase in cell division cycle. If cells in this phase are irradiated, chromosomal aberrations are of the chromosome type, i.e., they involve both chromatids of a chromosome as shown in Fig. Among them a fragment (Fr), a dicentric (Dic), a centric ring (Rc), and translocation (Tr) are generally used as indicators in radiation dosimetry. Chromosomes with 3 or more (n) centromeres are also induced by radiation. They are treated as multidicentrics for convenience sake, and are counted as 2 or more (n-1) dicentrics. Tr is a stable aberrations to be inherited by daughter cells while Dic, Rc, and Fr are unstable, to be lost during cell division. Theoretically, Tr and Dic accompanied by Fr are induced by radiation in the equal ratio.The background frequency of Dic and Rc is very low, about one Dic plus Rc in 1000 cells. A fragment caused by deletion is called as an excess fragment (exFr). The background frequency of Tr and exFr is much higher than Dic and Rc. In general, Dic and Rc accompanied by a fragment are specific markers of radiation exposures, while Tr and exFr are of all kinds of chromosomal mutagens. The yield (Y) of chromosome aberrations (exFr, Dic, Rc and Tr) is related to dose (D) by the equation as follows: Y=A+ alfaD + betaD2where A is background yield, alfaD is aberrations induced by a single track of radiation, and betaD2 is aberrations produced by two or more tracks of radiation. Coefficients alfa, and beta can be obtained by an experimental study analyzing chromosome aberrations in the irraditated blood. This equation can be applied up to the doses about 6 Gy in low LET radiation where the yield of Dic saturates because of the limitation of chromosome number (46) of a man as well as cell death. In the low linear energy transfer (LET) radiation such as X-rays or gamma rays, the dose response relationship of Dic becomes linear at low doses and quadratic at high doses. In high LET radiation such as neutrons (n in Fig. 2), protons, and gamma-rays, the dose response relationship of Dic becomes rather linear. When the dose is the same , the higher the LET, the more the yield of Dic. The yield of Dic increases with the decrease of energy if the sort of radiation is the same (for example, uppermost 3 lines in Fig 3). In case of Low LET radiations, the yield of Dic decrease when the dose rate becomes lower (lowermost 2 lines in Fig. 2). On the other hand, the effect of the dose rate is not significant in the case of high LET radiation. Analyzing the yield of chromosome aberration also makes it possible to estimate the size of the exposed portion in the body and the exposed dose in the past. The increase of the yield of Dic was detected at the dose of 2 cSv in acute exposures in vitro and at the dose rate of about 1 cSv per year in chronic exposures in vivo. Typical cases of dose estimations performed by chromosome analysis will be presented.International Symposium on Innovative Technology for Radiation Risk Study 200

    ISO Standard for Laboratories performing Biological Dosimetry by Cytogenetics

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    NIRS Workshop on Cytogenetic Biodosimetry for Asia & 46th ISTC Japan Workshop NIRS-ISTC Workshop on Cytogenetic Biodosimetr

    Cytogenetic scar by low dose exposure inTokai-mura criticality accident

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    放射線生物学とイメージングに関する第4回日仏ワークショッ

    Dose estimation by chromosome analysis of neighbors and low-dose exposed persons

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    Dose estimation by chromosome analysis

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    Detectable Low Dose Limit in Health Effect Predicted by The Study on The Background Frequency of Chromosome Aberrations.

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    Positive relation between risk of cancer and the frequency of chromosome aberrations in lymphocytes has been shown by the follow up studies on the subjects whose chromosomes were analyzed (reviewed by S. Bonassi. et al., Cytogenet Genome Res., 2004). There are increasing evidences showing the higher frequency of chromosome aberrations (translocations) in the peripheral lymphocytes of the individuals exposed to the environmental clastogens such as the gasses in traffic air pollutions (O. Beskid et al., Mutat Res. 2007) as well as smoking (W. Zhang et al., J. Radiat. Res. 2004; A. J. Sigurdson et al., Mutat. Res. 2008) when such frequency was compared with that of less exposed to them. Under the China-Japan collaborative studies, we analyzed the frequencies of translocations in the peripheral lymphocytes of the residents in the high natural background radiation area and its control areas in a remote village, and of the residents in a large city. The frequencies were high in all the categorized sub-groups. Individual variation among subjects within a sub-group was large. Effects of the high levels of natural background radiation were small, and invisible due to the large effects of clastogenic factors in the normal living circumstances (W. Zhang et al., J. Radial. Res. 2003; C. Wang et al., China Occupational Medicine, 2008). Chromosome aberrations are routinely used for the estimation of exposed doses in cases of radiation accidents. Science radiation doses can be calculated by the dose response curves of chromosome aberrations, the frequencies of translocations analyzed by us were converted to radiation doses assuming that all those translocations had been induced by radiation. D.C.Lloyd and A.A. Edwards. (1983) reported that the induction rate of dicentrics by chronic low dose gamma irradiation is about 2.5 in 10,000 cells per cSv. In case of acute exposure the frequency follows the dose response shown as :Y = 2.31x10^-4^D + 6.33 x10^-6D^2^(M.S.Sasaki et al., J.Radial.Res. 2000).where Y is the frequency of dicentrics per 1,000 cells, and D is the dose in cSv. Because translocations and dicentrics are induced by radiation in about equal frequency (W. Zhang and I. Hayata, J. Hum. Genent. 2003),those dose response relations of dicentrics were used for the calculation of radiation dose from the frequency of translocations. The subjects in the present report consist of 20 elders (61.2 year-old on the average) in a large city and 16 elders (64.4 year-old on average) and 8 children (12.3 year-old on the average) in the control group in the remote village. They were all non-smokers who had no history of radiation exposure except for the natural background radiation or routine medical diagnostic procedures such as chest X-ray examination. Based on the calculated doses from the background frequencies of translocations in the lymphocytes and their standard deviations, the detectable low dose limit in health effects is discussedNIRS International Symposium on the Effects of Low Dose Radiatio
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