M Delbos

Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Fontenay, Île-de-France, France

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Publications (16)18.56 Total impact

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    ABSTRACT: The purpose of this study was to evaluate the in vivo dose-response relation of chromosome aberration formation and distribution in a context of localised and fractionated radiotherapy. Cytogenetic analysis was applied to eight patients, all treated for the same tumour localisation; the same localisation was used to prevent the variability usually observed between patients treated with radiotherapy and to allow the corresponding roles of the size of irradiation field and of the dose rate to be studied. The yield of dicentrics, centric rings and fragments was measured in blood samples taken before treatment, during the course of radiotherapy and up to 6 months after. After the first fraction of radiotherapy, we observed that the whole-body dose estimated from the yield of dicentrics and rings was higher (0.35+/-0.2 Gy) than the calculated equivalent whole-body dose (0.07+/-0.04 Gy). By contrast, the partial-body dose derived from the Qdr (quotient of dicentrics and rings) model was estimated to be 2.2+/-0.3 Gy, which agreed quite well with the dose delivered to the tumour (2.1+/-0.1 Gy). We also found a correlation between the yield of induced chromosome aberrations and the target field size (p = 0.014). U-value analysis showed that the distribution of dicentrics and rings was overdispersed, despite the fractionation of the exposure, and a positive correlation between the U-value and the dose rate was observed (p = 0.017). Overall, these results suggest that the proportion of undamaged lymphocytes could increase with the dose rate.
    The British journal of radiology 09/2010; 83(993):759-66. · 2.11 Impact Factor
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    ABSTRACT: The purpose of this study was to evaluate the in vivo dose-response relation of chromosome aberration formation and distribution in a context of localised and fractionated radiotherapy. Cytogenetic analysis was applied to eight patients, all treated for the same tumour localisation; the same localisation was used to prevent the variability usually observed between patients treated with radiotherapy and to allow the corresponding roles of the size of irradiation field and of the dose rate to be studied. The yield of dicentrics, centric rings and fragments was measured in blood samples taken before treatment, during the course of radiotherapy and up to 6 months after. After the first fraction of radiotherapy, we observed that the whole-body dose estimated from the yield of dicentrics + rings was higher (0.35 +/- 0.2 Gy) than the calculated equivalent whole-body dose (0.07 +/- 0.04 Gy). By contrast, the partial-body dose derived from the Qdr (quotient of dicentrics and rings) model was estimated to be 2.2 +/- 0.3 Gy, which agreed quite well with the dose delivered to the tumour (2.1 +/- 0.1 Gy). We also found a correlation between the yield of induced chromosome aberrations and the target field size (p = 0.014). U-value analysis showed that the distribution of dicentrics and rings was overdispersed, despite the fractionation of the exposure, and a positive correlation between the U-value and the dose rate was observed (p = 0.017). Overall, these results suggest that the proportion of undamaged lymphocytes could increase with the dose rate.
    The British journal of radiology 06/2010; · 2.11 Impact Factor
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    ABSTRACT: To compare translocation rate using either M-FISH or FISH-3 in two patients treated for head and neck cancer, with a view to retrospective dosimetry. Translocation analysis was performed on peripheral blood lymphocyte cultures from blood samples taken at different times during the radiotherapy (0 Gy, 12 Gy and 50 Gy) and a few months after the end of the treatment (follow-up). Estimated translocation yield varied according to the FISH technique used. At 50 Gy and follow-up points, the translocation yields were higher with FISH-3 than with M-FISH. This difference can be attributed to three events. First, an increase in complex aberrations was observed for 50 Gy and follow-up points compared with 0 Gy and 12 Gy points. Second, at the end of treatment for patient A, involvement of chromosomes 2, 4, 12 in translocations was less than expected according to the Lucas formula. Third, a clone bearing a translocation involving a FISH-3 painted chromosome was detected. More translocations were detected with M-FISH than with FISH-3, and so M-FISH is expected to improve the accuracy of chromosome aberration analyses in some situations.
    Journal of Radiation Research 10/2007; 48(5):425-34. · 1.45 Impact Factor
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    ABSTRACT: In case of an accidental overexposure to ionizing radiation where the dose received by the victim is over 5 Gy, the conventional biological indicator of dose, the dicentric assay, does not provide an accurate enough dose measurement. A more appropriate technique is to measure ring chromosomes in stimulated lymphocytes. Dose-effect relationships were obtained by plotting the frequencies of Premature Chromosome Condensation (PCC)-rings in PCC lymphocytes obtained by chemical induction with Calyculin A in vitro, irradiated with doses between 5 to 25 Gy. Cells were exposed either to neutron or to gamma rays and the corresponding dose effect curves are presented in this paper for the first time in literature. For the elaboration of these curves, 9 675 PCC cells in G1 G2 and M/A stages were analysed. The results were fitted to a lineal model in gamma irradiation up to 25 Gy. For neutron irradiation the data was fitted to a lineal model up to 10 Gy, and then dose saturation was observed. In conclusion, with this technique it is possible to set up dose effect curves up to 25 or 10 Gy according to the gamma or neutron radiation.
    Journal of Radiation Research 02/2007; 48(1):1-6. · 1.45 Impact Factor
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    ABSTRACT: The purpose of this study was to examine a new approach to retrospective biological dosimetry, by using a long-term animal model to determine the stability of translocation frequency after in vivo irradiation. While the frequency of dicentrics is known to decrease over time, the persistence of more stable chromosomal aberrations such as translocations could be useful if their stability were definitively proved. Four monkeys (Macaca fascicularis) were exposed to two different doses of ionizing radiation: 2 Gy whole body irradiation for two and 4 Gy for two others. Blood samples were obtained at various times after irradiation. Both total and two-way translocations were detected by fluorescence in situ hybridization. Translocations were scored in stable cells, that is, those without dicentrics, rings or fragments. The course of translocation frequency was analysed at four time-points: one hour (H1), 2 months (M2), 10 months (M10) and 31 months (M31) after irradiation. We observed two separate trends in translocation frequency: Total translocation frequency decreased slightly in animals irradiated with a dose of 2 Gy, while two-way translocation frequency was relatively stable in all irradiated animals. We confirmed the long-term stability of translocations and found that it seems to depend on the type of the translocation recorded. Overall translocations were stable for up to 31 months regardless of dose, but two-way translocations were more stable than those that were non-reciprocal, especially in stable cells.
    International Journal of Radiation Biology 08/2006; 82(7):493-502. · 1.90 Impact Factor
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    ABSTRACT: To compare the efficiency of different cytogenetic tools in estimating the doses received by four people involved in the Lilo accident and to monitor the dose estimate over 4.5 years. Several young Georgian frontier guards handled at least one of the 12 Caesium sources found in a former Russian military camp. Overexposure lasted from July 1996 to May 1997. The Institute for Radiological Protection and Nuclear Safety (IRSN) obtained blood samples taken at several intervals post-exposure from the four most highly-exposed people. Dose estimation was performed using dicentric and translocation scoring. The first dose estimations performed by dicentric scoring gave whole-body doses ranging from 0.4 to 1.3 Gy. Overexposure was complex and several mathematical models were used to take this complexity into account. This could provide information concerning the circumstances of overexposure. Concerning follow-up, the yield of dicentrics decreased by about 50% in the first 4 months following the end of overexposure whereas translocations were stable over the period of analysis. It has been useful to compare cytogenetic results with clinical results. The results presented here reveal good stability of translocations. However the first dose estimation was not attempted until 6 months after the last exposure.
    International Journal of Radiation Biology 02/2006; 82(1):39-48. · 1.90 Impact Factor
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    ABSTRACT: We propose a new method of biodosimetry that could be applied in cases of localized irradiation. The approach is based on excess chromosome segments determination by the PCC-FISH technique in fibroblasts isolated from skin biopsy. Typically, 0 to 10 Gy ex vivo gamma-irradiated human skin biopsies were dissociated and fibroblasts were isolated and grown for several days. Cells next underwent PCC-FISH painting of whole chromosome 4, and the number of excess chromosome segments per metaphase was determined. An ex vivo reference curve correlating the number of excess chromosome segments per metaphase to the radiation dose was established and used to assess the dose delivered to the skin of one of the victims of the radiological accident that occurred at Lia in Georgia in December 2001. Specifically, the victim suffering from moist desquamation underwent skin excision in Hospital Percy (France). Measurement of excess chromosome segments per metaphase was done in fibroblasts isolated and grown from removed wounded skin and subsequent conversion to radiation doses was performed. The radiation dose map obtained was shown to be in accordance with clinical data and physical dosimetry as well as with conventional biodosimetry. These results demonstrated that PCC-FISH painting applied to skin fibroblasts may be a suitable technique for dose estimation. To assess its worth, this approach needs to be extended to future accidents involving localized radiation exposure.
    Radiation Research 11/2004; 162(4):365-76. · 2.70 Impact Factor
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    ABSTRACT: The purpose of this paper is to investigate how well various assays on blood can detect radiation dose to people exposed many years previously and, if possible, to estimate that dose. The assays were applied to persons resident close to Chernobyl in 1986. Blood samples were taken 13-15 years after the reactor accident. The assays used were the frequencies of lymphocyte chromosomal translocations, micronuclei, HPRT mutations and apoptotic cells. Translocation yields in the exposed groups were marginally higher than in their respective controls, leading to dose estimates of about 0.2 Gy but with large uncertainties. All other assays showed inconsistency from person to person or other variations apparently not related to dose. The measurement of translocations, it is concluded, is the biological method of choice for retrospective dosimetry.
    Radiation Protection Dosimetry 02/2004; 111(2):211-9. · 0.91 Impact Factor
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    ABSTRACT: The Institute of Radiation Protection and Nuclear Safety (IRSN) organized a biological dosimetry international intercomparison with the purpose of comparing (i) dicentrics yield produced in human lymphocytes; (ii) the gamma and neutron dose estimate according to the corresponding laboratory calibration curve. The experimental reactor SILENE was used with different configurations: bare source 4 Gy, lead shield 1 and 2 Gy and a 60Co source 2 Gy. An increasing variation of dicentric yield per cell was observed between participants when there were more damages in the samples. Doses were derived from the observed dicentric rates according to the dose-effect relationship provided by each laboratory. Differences in dicentric rate values are more important than those in the corresponding dose values. The doses obtained by the participants were found to be in agreement with the given physical dose within 20%. The evaluation of the respective gamma and neutron dose was achieved only by four laboratories, with some small variations among them.
    Radiation Protection Dosimetry 02/2004; 110(1-4):471-6. · 0.91 Impact Factor
  • Radioprotection 01/2003; 38(3):323-340. · 0.44 Impact Factor
  • Radioprotection 01/2002; 37(1):27-40. · 0.44 Impact Factor
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    ABSTRACT: Because of the large number of cells to be analyzed in cases of overexposure to ionizing radiation, an automated imaging system is desirable for scoring both translocations and dicentrics. This system should include three essential steps: automatic metaphase finding, automatic image capture at high magnification, and, finally, optimized data analysis for aberration interpretation. We evaluated a new image analysis system (CYTOGEN, IMSTAR, France) and found that its metaphase finder saved time, as much as quadrupling the speed of scoring chromosomal aberrations. Automatic metaphase selection did not appear to induce bias. We confirmed the equivalence of observing aberrations on a screen after automatic image capture and direct observation under a microscope. This work validated all of the steps necessary for obtaining images for automatic chromosomal aberration detection. The protocols for the detection of translocations may now be applied for biological dosimetry. This step will be validated in a future study.
    Journal of Radiation Research 07/2001; 42(2):165-77. · 1.45 Impact Factor
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    ABSTRACT: When accidental exposure to ionizing radiations is suspected, optimal choice of a treatment strategy requires, in addition to information about the clinical signs and physical dosimetry, a determination by biological parameters of the dose received. The scoring of unstable chromosomal aberrations in peripheral blood lymphocytes is the current reference method. Preparation of these samples depends on the goal sought--an exact assessment of several irradiations or rapid triage in the case of a large-scale accident. Moreover, some adaptation may be necessary if the irradiation is either heterogenous or not recent. Despite the robustness and adaptability of this procedure, conventional cytogenetics remains a tedious and time-consuming technique, and it requires specialized staff. Scoring micronuclei in binucleated lymphocytes may be an easier, simpler altemative to a dicentric assay. This paper, which is based on the experience acquired by the IPSN in recent years in expert assessment of suspected radiations, has as its goal to provide a succinct technical guideline of these different approaches, as they are adapted to suspected recent irradiation and triage.
    Cellular and molecular biology 06/2001; 47(3):557-64. · 0.81 Impact Factor
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    ABSTRACT: In the case of an irradiation suspicion implying few people and considering the known (or unknown!) circumstances of the radiological accident, the quality of the preparations and the precision of the estimate are privileged. So that the confidence interval is satisfactory, several hundreds of metaphases must be observed. It is a long and tiresome job, requiring several working days for skilled observers. In the event of accident involving a large population exposed to irradiation, uncertainties of physical dosimetry or clinical symptoms increase in proportion of the number of potentially irradiated individuals, which justifies the interest of a biological dosimetry on a purely individual basis. Its utility fully appears only if the dose estimates can be returned in the hours following the real or supposed irradiation. The measuring accuracy and the quality of the preparations appear in proportion less important than the deadline. A particular procedure making it possible to combine these various factors was developed and checked during simulation training. The metaphase preparation and chromosome analysis techniques were simplified, and the number of observed metaphases reduced. We will see below the effectiveness of this process.
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    ABSTRACT: Dose-effect curves for dose assessment in Gamma and neutron overexposures to high doses are presented in this paper for the first time in literature. The relationships were obtained by plotting the Premature Chromosome Condensation -rings (PCC-R) frequencies in PCC lymphocytes obtained by chemical induction with Calyculin A in vitro, with radiation doses between 5 to 25 Gy. For the elaboration of these curves 9 676 PCC cells in G1 G2 and M stages were analyzed. The results were fitted to a lineal quadratic model in Gamma irradiation. For neutron irradiation the data was fitted to a lineal quadratic model up to 10 Gy, and then a markedly cell cycle arrest and saturation was observed. These curves are of particular interest for victims exposed to doses exceeding 5 Gy where it is always very difficult to estimate a dose using the conventional technique.
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    ABSTRACT: Fluorescence in situ hybridisation (FISH painting) has enabled the detection of most of the stable radiation-induced chromosome aberrations (translocations, insertions). However, there is still no consensus about the use of FISH techniques for biological dose reconstruction. At IPSN, two cocktails of three whole human chromosomes paints were used for both in vitro and in vivo studies (i.e. 2, 4 and 12 for humans and 1, 4, 13 for rhesus monkeys). For human analysis, three in vitro dose-effect relationships were established using the same irradiation source (? rays, 60Co, 0.1 Gy.min-1 and 1 Gy.min-1). In vitro , the relative importance of complex exchanges was found to be negligible below 3 Gy. A x2 test was applied to the data corresponding to one of the calibration curves (1 Gy.min-1) in order to test the difference between the three chromosome radiosensitivities. No real experimental evidence was found for doubting that aberrations occurred in proportion to their DNA content (p>0.05). In vivo , the temporal persistence of translocations was studied in humans and rhesus monkeys. For human accidental irradiation, less dicentrics than translocations were generally found when the cytogenetic analysis was carried out after more than 2-4 months. Nevertheless, these translocation values rarely exceeded the estimated translocation background level (2.4 x 10-3 per cell). More information about the temporal persistence of translocations was obtained by FISH analysis of highly irradiated rhesus monkeys 4-7 years before blood sampling. The dose estimation based on translocation scoring using FISH triple-painting was underestimated according to the initial physical dose of irradiation. This underestimation appeared smaller when only the complete reciprocal translocations were taken into account for the dose estimates.