Dynamic analysis of chromosome aberrations in three victims of the Tokai-mura criticality accident.

Purpose: To investigate the dynamics of chromosome aberrations in the blood cells of three workers severely exposed to neutrons and gamma rays in a criticality accident that occurred in Tokai-mura, Japan, in 1999.Materials and methods: The change with time of the frequency of chromosome aberrations in the three patients was examined using a new analysis to score drug-induced prematurely condensed ring chromosomes (PCC-R) and a conventional metaphase analysis.Results: The frequencies and cellular distributions of PCC-R, dicentrics and rings did not change significantly among the samples obtained at 9-48h after the accident while the first depletion of lymphocytes occurred. The distributions of these aberrations in the cells of two patients showed a slight overdispersion compared with a Poisson distribution reflecting neutron and non-uniform exposures. The dose-response curve of rings paralleled that of dicentrics, but not PCC-R. The half-lives of PCC-R (8.5 months) and of rings (8.7 months) were shorter than that of dicentrics (13.5 months).Conclusions: In the three patients of the Tokai-mura accident, lymphocytes in the circulating and extravascular pools had reached equilibrium at 9h, and highly damaged lymphocytes did not selectively move away from the circulatory system during the first rapid depletion of lymphocytes after exposure. Data on the in vivo half-life of PCC-R as well as dicentrics and rings obtained in the present study may be useful for retrospective dosimetry

Low-cost metaphase finder system

In biological dosimetry by counting chromosome aberrations at low dose radiation exposure, automation technique has been required to process large number of sample preparations. The metaphase finder is an automated optical microscope system, which automatically scans and finds metaphase cells on the slide glass in low magnification, and relocates metaphase cells to the center of the field of view of the microscope to observe chromosomes in high magnification. The authors have constructed a cost-effective metaphase finder system by assembling commercially available components, such as microscope, motorized sample stage, personal computer and general purpose image analysis software package, instead of purchasing one dedicated system. The new system has high cost-effectiveness and high flexibility in adapting to the new staining methods. The mathematical morphology based image processing to the algorithm was used to find metaphase cells. Especially, the morphology for the gray-image was used for the newest version. The performance of this metaphase finder system was tested. The new machines were distributed to six institutes of The Chromosome Network for biodosimetry in Japan for the testing the new algorithm for the practical use. The scanning speed was 14.5 to 18.1 minutes per square centimeter. It was slower than several commercial metaphase finders but false positive were enough small. This system is economical and satisfactory for practical use

Structural analysis of radiation-induced chromosome aberrations by atomic force microscope (AFM) before and after Giemsa staining

12th International Congress of Radiation Researc

Cytogenetical dose estimation for 3 severely exposed patients in the JCO criticality accident in Tokai-mura.

A dose estimation by chromosome analysis was performed on the 3 severely exposed patients in the Tokai-mura criticality accident. Drastically reduced lymphocyte counts suggested that the whole-body dose of radiation which they had been exposed to was unprecedentedly high. Because the number of lymphocytes in the white blood cells in two patients was very low, we could not culture and harvest cells by the conventional method. To collect the number of lymphocytes necessary for chromosome preparation, we processed blood samples by a modified method, called the high-yield chromosome preparation method. With this technique, we could culture and harvest cells, and then make air-dried chromosome slides. We applied a new dose-estimation method involving an artificially induced prematurely condensed ring chromosome, the PCC-ring method, to estimate an unusually high dose with a short time. The estimated doses by the PCC-ring method were in fairly good accordance with those by the conventional dicentric and ring chromosome (Dic+R) method. The biologically estimated dose was comparable with that estimated by a physical method. As far as we know, the estimated dose of the most severely exposed patient in the present study is the highest recorded among that chromosome analyses have been able to estimate in humans

Chromosome analysis in three patients.

Dose estimation for the 3 severely exposed cases was performed by chromosome analysis. The whole body dose of radiation they had been exposed to was an unprecedented much higher dose than we had encountered in previous radiation accidents. The rate of lymphocytes in the white blood cells in two of the cases was so low that we could not culture and harvest cells by the conventional method. We took two specific measures to break through this difficulty. First, to collect a sufficient number of lymphocytes necessary for chromosome preparation, we processed blood samples by a modified method called the high-yield chromosome preparation method. Secondly, the dose estimation was made by two methods: a new method of scoring the PCC-ring and an ordinary dicentric and ring chromosome (Dic+R) counting method. The quickly but crudely obtained result by the former was in good agreement with the result obtained by the more time-consuming but well established latter method. The biologically estimated dose was comparable with the dose estimated by the physical method. As far as we know, the estimated dose of the most severely exposed case in the present study is the highest known record to date of dose chromosome analyses could assess in human radiation exposures