Estimation of Absorbed Doses on the Basis of Cytogenetic Methods
Vladimir A. SHEVCHENKO, Galina P. SNIGIRYOVA*, Alexander V. RUBANOVICH
N.I. Vavilov Institute of General Genetics, Russian Academy of Sciences
Gubkin st. 3, 117809 Moscow, Russia: shevchenko@vigg.ru*Moscow Research Institute of Diagnostics and Surgery,
Ministry of Health and Medical Industry of the Russian Federation, Moscow
stimulated human peripheral blood lymphocytes.
Single breaks of DNA molecules result in theoccurrence in metaphases of chromosome fragments
clearly revealed by the cytogenetic analysis. It is
important to note that ionizing radiation induces
damages affecting both chromosome chromatids,
which leads to the appearance of paired fragments (incontrast to single fragments resulting from the damageof one chromatid, which is most often observed under
the influence of UV-rays and chemical mutagens). In
case there are two and more breaks of DNA molecules
in a cell, the broken ends can recombine, creating new
rearranged chromosomal structures (dicentricchromosomes, ring chromosomes, translocations,inversions, deletions). With the usual methods ofchromosome staining, the most clearly recorded undera microscope are dicentric chromosomes (achromosome rearrangement with two centromerestaking place due to the association of two broken
chromosomes) and centric ring chromosomes (achromosome closed in a ring as a result of two breaks at
the ends of this chromosome). As a rule, such
chromosome rearrangements are accompanied bypaired fragments (acentric terminal parts ofchromosomes). Analysis of the frequency of such
easily detectable chromosomal rearrangements inmetaphases has formed the basis for the developmentof methods of biological dosimetry.
Two types of chromosome aberrations can occur
under the influence of radiation: unstable (dicentrics,
centric rings, acentric fragments) and stable(symmetric translocations, pericentric inversions etc.).
The occurrence frequency of unstable aberration,
namely dicentrics [10], is most often used to estimate
absorbed doses. Sometimes the analysis takes into
account centric rings, but their frequency isinsignificant in comparison with the frequency ofdicentrics (approximately 5-10%) [11].
The advantage of the analysis of the level ofdicentrics in biodosimetric studies is that they areeasily found with a optical microscope without using
special methods of processing and staining. One of therequirements for correct application of this method of
dosimetry is to analyse metaphases of the first cell
cycle. This is due to the fact that during cellproliferation about 50% of dicentrics are lost during thefirst postradiation division. The control of the cell cycle

Introduction
Long-term studies in the field of radiation
cytogenetics have resulted in the discovery of
relationship between induction of chromosome
aberrations and the type of ionizing radiation, theirintensity and dose. This has served as a basis of
biological dosimetry as an area of application of therevealed relationship, and has been used in the practiceto estimate absorbed doses in people exposed toemergency irradiation [1,2]. The necessity of using themethods of biological dosimetry became most pressing
in connection with the Chernobyl accident in 1986, as
well as in connection with other radiation situations
that occurred in nuclear industry of the former USSR.
The materials presented in our works [3-8]demonstrate the possibility of applying cytogenetic
methods for assessing absorbed doses in populations ofdifferent regions exposed to radiation as a result ofaccidents at nuclear facilities (Chernobyl, the village
Muslyumovo on the Techa river, the Three Mile Island
nuclear power station in the USA where an accident
occurred in 1979). Fundamentally, new possibilities for
retrospective dose assessment are provided by the
FISH-method that permits the assessment of absorbed
doses after several decades since the exposure occurred[7]. In addition, the application of this method makes it
possible to restore the dynamics of unstable
chromosome aberrations (dicentrics and centric rings),
which is important for further improvement of themethod of biological dosimetry based on the analysis
of unstable chromosome aberrations [9].
The purpose of our presentation is a brief
description of the cytogenetic methods used inbiological dosimetry, consideration of statisticalmethods of data analysis and a description of concrete
examples of their application.

1. Analysis of chromosome aberrations for the
purposes of biological dosimetry
Under the action of radiation the genetic materialsof the human organism, as well as any livingorganisms, experience damages of DNA molecules
resulting in chromosome breakage and further invariouschromosomal
rearrangements.
Suchrearrangements of chromosomes are observed visuallyin metaphases of dividing cells, for example, in216

was performed with propidium iodide (PI) in antifade
solution.
Conventional chromosome analysis was carried out
exclusively in complete first division metaphases (M1)
identified by uniformly stained sister chromatids.
Recorded were all types of chromosomal damage but
data are presented only for dicentrics and ring
chromosome. About 300 cells were scored from eachexamined clean-up worker, each irradiated individualfrom contaminated regions and each control subject.
For scoring FISH-painted exchanges, each metaphasespread was analyzed with a filter set allowing asimultaneous observation of FITC and PI fluorescence.
The blue AMCA fluorescence of the bounddigoxigenin-labeled pancentromeric probe wasvisualized by using an ultraviolet excitation filter.
Chromosome morphology was additionally checkedwith a filter set providing only PI fluorescence.
Depending on the quality of FISH-painting between
300 and 2,000 complete metaphases were scored fromeach donor. Rearrangements involving painted target
chromosomes (yellow) and any other PI stained (red)chromosomes can be easily detected as two-colored
structures (yellow/red). Two-colored chromosomeswith one blue AMCA centromeric signal wereclassified either as complete or incomplete
symmetrical translocations or insertions. Two-coloredchromosomes with two centromeric signals wereclassified as dicentrics, dic(AB).
Genomic frequencies, FG, for symmetricaltranslocations or dicentrics were calculated from thefrequencies, Fp, of painted translocations or dicentrics
for the target chromosomes by inversion of theequation Fp=2.05fp(1-fp) FG earlier applied by Lucaset al. [20] where fp=0.192 is the fraction of DNA
contained in the painted chromosomes.

with the use of special differential staining ofchromosomes (FPG-method) allows us to avoid thismistake [12].
The spontaneous level of dicentrics ischaracterized by rather low values. Thus, the data on arelative level of dicentrics widely reported inpublications show a significant interlaboratory
variability of this value. The dicentric frequency incontrol groups may vary from 0 to 2.35⋅10-3 per cell[11]. The average value of the frequency of dicentrics
is within the range of 0.3-0.5⋅10-3 per cell. Lloyd et al.
[13] analyzed the data on the frequency of dicentrics incontrol groups of donors that were obtained in 65
different laboratories. An average dicentric level (theextreme values were not taken into account) made up
0.55⋅10-3 per cell. In our experiments the spontaneous
frequency of dicentrics for 82 donors having no contact
with ionizing radiation made up 0.1-0.2 per 1,000 cells(26,849 metaphases analyzed). Thus, it is necessary toobtain reliable results on the spontaneous frequency ofdicentrics in laboratories engaged in biologicaldosimetry in order to do correct assessment of radiation
doses.
In experiments with animals [14] and in cytogenetic
examinations of patients subjected to radiation therapy[15,16], it was shown that the frequency of dicentrics inlymphocytes of peripheral blood was comparable upon
irradiation in vivo and in vitro. This fact is the mainprerequisite for the use of calibration «dose - effect»
curves obtained in vitro in biological dosimetricstudies .
Special cytogenetic methods have been developed
to register other exchange chromosome aberrations(inversions, deletions, translocations). The best known
methods are G-banding and FISH. The latter wasapplied in our studies and therefore we shall discuss
here the potentialities of this method.
In our experiments lymphocyte cultures andchromosomes preparation were prepared according tostandard procedures [1]. Slides prepared for FISH
analyses were stored at -20° C under nitrogen
atmosphere until use. Slides for conventional analyses
were stored for 5 days at room temperature and werethen subjected to standard fluorescence plus Giemsa(FPG) staining.
Plasmid DNA of chromosome specific Hind III
pBS libraries of human chromosomes 1, 4 and 12 [17]was biotinylated [18]. A degenerate a-satellite DNA
pancentromeric probe was produced by in vitro
amplification using a polymerase chain reaction (PCR)
and labeled with digoxigenin [19]. Hybridization,
detection of bound biotin-labeled painting probes forthe target chromosomes with streptavidin-fluorescein
isothyocyanate (FITC) conjugate and the bounddigoxigenin-labeled pancentromeric probe with
AMCA-labeled (7-amino-4-methylcoumarin-3-aceticacid) antibodies were carried out [19]. Counterstaning

2. Statistical methods of biodosimetry
When processing the results of cytogenetic studies
of exclusive importance is the choice of adequate
methods of mathematical statistics. This is associatedwith specific difficulties faced when comparing thefrequencies of rare events. Numerous discussions
about the methods of biodosimetry and radiobiology ofsmall doses concerned, in the majority of cases, theproblems of reliability of statistical interpretations [21].
Statistical processing of the results of cytogenetic
analysis includes two necessary stages:
1) Calculation of the level of significance ofdifferences between irradiated and control groups of
persons.
2) Evaluation of irradiation doses at the individualand group levels using calibration.

2a. Statistical significance of observed
differences in aberration frequencies
217

Statistical analysis of cytogenetic data should begin
with considering the question about the reliableinterval of the aberration frequency in the irradiatedgroup. In the case of processing cytogenetic data, thisstandard procedure has a number of specific features.
We shall enter necessary designations. Let N0 cells
be examined for the control group, and n0 cells withchromosome aberrations be found among them. We
shall designate the corresponding numbers for theirradiated persons as N1 and n1. Then the frequencies ofu = ϕ −ϕ01

in the control and in the experiment, the primaryestimation of χ2 can be reduced to a very simple
formula:(n − n 0 )χ2 ≈ 1n 0 + n1

There is a very essential restriction for theapplication of the χ2 criterion in processing the resultsof cytogenetic analysis. The number of cells withaberrations both in the experiment and in the control(n0 and n1) should be more than 5. If this condition is
not met, the χ2 values may be overestimated and, thus,
the significance of differences. On the other hand, with
sufficiently large values of n0 and n1, the χ2 criterion is
as conservative as the Student’s test. Therefore, whenprocessing the results of cytogenetic analysis, it ispreferable to use the exact Fisher criterion, which
although complicated permits any doubts to be
removed in all situations.
The essence of this universal method consists inexact calculation of the probability of occurrence ofobserved differences under the assumption that theirradiated and control groups are indiscernible by theaberration frequency. According to the combinatorial
theory of probabilities with the given assumption, theprobability of detecting in the control no more than n0of cells with aberrations is equal to

N N
0 1
N +N
0
1

cells with chromosome aberrations are p0= n0/N0 and
p1=n1/N1. For their comparison various modificationsof the Student’s criterion are frequently used. For
example, u-statistics is calculated by the formulawhere

ϕ i = 2arcsin p i, i = 0, 1.

The differences can be considered as significant, if theobtained value u is higher than 2.
However, the real aberration frequencies are sosmall that the standard parametric criteria become tooconservative. For example, with the same number of
estimated metaphases (N0=N1) the value u isapproximately

n C N 0C N 1
0
k
n−k
P= ∑
N
C
k =0
n

u ≈ 2 ( n1 − n 0 ) .
It means, that 9 cells with aberrations in theexperiment do not statistically differ from 4 in control
cells with any volume of examined material. At thesame time the use of finer statistical tests can lead to
opposite results. It seems that in processing of
cytogenetic data one should completely abandon theStudent’s criterion and use nonparametric methods.
In some cases, it is enough to use the χ2 - test which
reduce to the calculation of the valueχ2 =(N 0 + N 1)(N 0 n1 − N 1n 0 ) 2

N 0N 1(N 0 + N 1 − n 0 − n1)(n 0 + n1)2

where ÑN
- is the number of combinations from N
nof elements on n, N =N0+N1 and n =n0+n1. This
probability defines the level of significance ofdifference by exact Fisher criterion [22]. With P <0.05, the aberration frequency in the control issignificant lower than in irradiated group (differences
are essentially nonrandom).
The formula for P includes the probabilities ofhypergeometric distribution, which describes theprobability of sample size n without returning to the setof size N. Upon sampling from a large set (N>>n),samples with returning can be replaced by samples
without returning. Thus, hypergeometric probabilities
are replaced by binomial ones, which considerably
reduces calculations. In the given approximation thelevel of significance is equal:.

The differences between the control and theexperiment are significant if the calculated value of χ2
is higher than 4. Otherwise, the observed differences
can be attributed to casual reasons.
In the analysis of cytogenetic data the number of
examined metaphases significantly exceeds the cellswith chromosome aberrations. In this case theexpression for χ2 is simplified:n0
P ≈ ∑ C n q k (1 − q ) n − kkk =0(N 0 n1 − N 1n 0 ) 22
χ ≈N 0N 1(n 0 + n1)

where q=N0/N. In this sum, the value of the term with
the number k=n0 exceeds the rest approximately by one

In practice, with same volume of examined material

218

Aberration frequency

y+1.96syy-1.96s

Dose
Dmin

D

Dmax

Fig 1. Calibration dose - effect curve with confidential intervals. A
scheme of determination of 95%-confidential interval of dose
estimation, corresponding to aberration frequency equal to y±s isgiven.
order of magnitude. It can be used for primaryy (1 − y )estimations of the significance of differences:s=n! N 0P ≈n !n !  N 
0 1

n0

n
 N 1 1


N 

N

is an average error in the aberration frequency y whena sample size is N. Then the upper ( lower ) estimate is
at a point of crossing of the level y+1.96 s (y-1.96 s)
with the lower (upper) confidential curve ofregression.

If this probability is higher than 0.05, the differences
between the experiment and the control cannot be
considered significant.
If the sample sizes in the experimental and control
groups are identical, the exact Fisher criterion allows
the following interpretation: P is the probability ofoccurrence of no more than n0 ‘heads’ upon nthrowings of a symmetric coin. Let, for example, twoaberrations be found in the control and 8 chromosome
aberrations in experimental group with identicalnumbers examined metaphases. Can such differences
arise for purely casual reasons? What is the probability
to make an error when asserting that the control groupdiffers from the experimental one? According to thelast formula, this probability is exactly equal to theprobability of occurrence of no more than two “heads”
in 10 throwings of a symmetric coin.

An alternative approach consists in complete
abandoning the application of regression equations anda direct use of calibration data presented in tabulated
form. The appropriate mathematical theory is rather
complex and uses Bayes’s approach [2]. The theory
permits a complete construction of the density
distribution of probability of dose estimation
corresponding to the observable frequency ofaberrations. Numerical examples show that thismethod, though preferable in mathematical rigidness,does not essentially change evaluations obtained by the
regression method [11].

3. Estimation of absorbed doses on the basis ofanalysis of unstable and stable chromosome
aberrations

2b. Estimation of irradiation doses on the basisof calibration data
Estimation of individual doses of irradiation by theaberration frequency can be conducted on the basis ofcomparison with previously obtained calibrated data.
As a rule, these data are presented by equations oflinear or linear-square regression. In this case, the dose
estimate is obtained as a result of simple substitution of
the observed aberration frequency in a corresponding
equation of regression. The procedure of determinationof confidence intervals for dose estimates is shown in
Fig. 1 taken from [1].
Let the observed aberration frequency is equal to y±s, where

The basis for application of cytogenetic methods inbiological dosimetry is a clear-cut dependence of thefrequency of chromosome rearrangements on the dosesof ionizing radiation, which has been repeatedly
demonstrated in experiments. Having at disposal suchdose dependencies obtained in vitro under the action ofdifferent kinds of ionizing radiation on cells(calibration curves), it is possible to attack the problem
to estimate absorbed doses in irradiated people byanalyzing the frequency of chromosome aberrations[1].
The pattern of a «dose - effect» curve for dicentrics
and other chromosomal aberrations depends on the219Table 1. Coefficients of the equation y = αD + β D2 for dicentrics obtained after irradiation ofhuman peripheral blood lymphocytes by various types of radiation.
Kinds of radiation
α ± S.E. [10-1Gy-1]
β ± S.E. [10-2Gy-2]
60
Co γ, (0.017 Gy/m)
0.090 ± 0.400
4.17 ± 0.28
60
Co γ, (0.5 Gy/m)
0.107 ± 0.041
5.55 ± 0.28
220 kV X-ray (0.5 Gy/m)
0.404 ± 0.030
5.98 ± 0.17
14.5 MeV neutrons
1.790 ± 0.150
7.40 ± 1.39
Fission spectrum neutrons, E=1.6 MeV
3.690 ±0.210
13.34 ± 1.73
Fission spectrum neutrons, E=0.7 MeV
8.350 ± 0.100
centric rings) for estimation of an irradiation dose ispossible mainly after a single rather uniform radiation
exposure in early (3-4 months) periods. So, in the workof Brewen et al. [23] the case of an emergency
irradiation from a 60Co source is described. Using thephantom and film-dosimetry the dose received by the
injured person was reconstructed. It made up 127 R.
On the basis of cytogenetic analysis the dose made up
144 R. The biological dose corresponded well to thedata physical dosimetry.

types of ionizing radiation and its energy
characteristics. The analysis of the generalized data ofdifferent authors on the dependence of the frequency
of dicentrics in peripheral blood lymphocytes on thedose and type of radiation is presented in the work by
D.C. Lloyd et al. [13].
For low-energetic radiation this dependence isusually described by the linear-quadratic equation y = c+ αD + βD2, where с is the spontaneous level ofdicentrics. For radiation with high LET the dose-effectdependence is linear y = c + αD. As an example, themean coefficients of the equations of calibration curves[11] are given in Table 1. The biological efficiency ofdifferent kinds of ionizing radiation can be judged by
the ratio of coefficients.

Retrospective estimation of doses by thefrequencies of unstable chromosome aberrations seems
to be problematic today. The basic reason is theelimination of cells with unstable aberrations fromcirculating blood. However there are works where
possible approaches for solving this problem are
discussed. These approaches are based on the analysisof the processes of elimination ofcells withaberrations, or on the analysis of the distribution ofaberrations among cells [24,25,9].
The data collected from cytogenetic examinationsof patients subjected to radiation therapy [26,27] andpeople injured as a result of accidents at nuclear
enterprises [28-31] have allowed the quantitativedescription of the processes of elimination of cells withunstable chromosome aberrations and to estimate theduration of the lymphocyte life. Unfortunately, thesedata are not unambiguous. The parameterscharacterizing the elimination of lymphocytes

The biological dose calculated on the basis of thefrequency of dicentrics with the use of a calibration
curve suitable for a given radiation situation isequivalent to the dose of acute uniform irradiation. The
lower limit allowing a reliable (95 % probability)
estimation of a dose (as a value equivalent to the doseof acute irradiation) depends on the number ofanalyzed cells, which is clearly demonstrated by Prof.
Bauchinger in Table 2. In reality, with the analysis ofabout 5,000 cells the lower limit of reliable dose
estimation is about 100 mGy for gamma - radiation and
50 mGy for fission spectrum neutrons.
Successful application of the analysis of thefrequency of unstable aberrations (dicentrics andTable 2. Cell number and significantly elevated dicentric frequencies as compared to a
background level (14 per 35,500 cells) required for the detection of a dose of 60Co γ-rays(0.5 Gy•min-1) with p = 0.05.
Cell number Dicentrics significant
Dose (Gy)
100
1
0.63
200
2
0.56
500
2
0.31
1000
3
0.24
2000
4
0.17
5000
6
0.10
10000
10
0.074
20000
17
0.056
50000
37
0.041
100000
70
0.033
220

in the given case). In principle, the study may involveother painted chromosomes as well. Depending on thesize of painted chromosomes and their number, theanalysis may include different portions of the entire
genome. The calculation of the translocation frequency
per whole genome is made using (as indicated in
section 1 of this work) the formula of Lucas et al. [20]which takes into account the size and number ofpainted chromosomes.
Using this methodology the absorbed doses havebeen evaluated for a group of 52 liquidators,
inhabitants of the Altai territory irradiated about 45
years ago from nuclear explosions on the
Semipalatinsk nuclear test site, and people living in theregion of the Three Mile Island power station at which
there was a nuclear accident in 1979 accompanied byan emission of radionuclides to the environment. The
results of these studies are presented in a special work.

considerably vary depending on individual
radiosensitivity of the donors, conditions of irradiationand the action of various additional environmental
factors. There is no universal curve, especially forcases of partial irradiation. Also there is a lot of
uncertainty in the estimation of the half-life period ofcells with unstable chromosome aberrations which
varies from 110 days to 4 years according to different
authors. In our studies on the estimation of the half-life
period of cells with unstable chromosome aberrations
by calculating the ratio of the frequency of stable
aberrations (estimated by the FISH method) to thefrequency of unstable aberrations, this period is 4 years[9]. Apparently, retrospective dose estimation on thebazis of the frequency of unstable aberrations can beused taking into account the elimination process ofcells with aberrations, when it is necessary to estimate
an average dose for a group of irradiated individuals. In
case of individual dosimetry, the dose can be
determined only with a rather wide confidence interval.
For the purposes of retrospective dose estimation
the FISH method is most often recommended atpresent. Stable chromosome aberrations revealed withthis method are not eliminated in time, therefore, thedose estimation based on the analysis of the frequencyof such stable chromosome aberrations (translocations)is possible within many years after exposure to ionizing
radiation.
Biological dose estimates were derived from anacute in vitro 137Cs gamma-ray calibration curve (doserate 0.5 Gy/min) for FISH-painted translocations(chromosomes 1, 4 and 12) obtained in the laboratoryof M. Bauchinger [19] modyfied taking into the data
for the control material obtained in our laboratory:
y= (0.96±0.27)⋅10-3 + (0.95±0.21)⋅10-2⋅D+ (1.45±0.14)⋅10-2⋅D2,
where y is the frequency of observed FISH-painted
translocations (chromosomes 1,4 and 12), D - theabsorbed dose, Gy. On the basis of this calibration
curve with the application of the FISH method, theestimation of absorbed doses in the Chernobyl
liquidators within 8-10 years from the irradiation was
carried out [7]. To this and, an experimentally obtained
value of the frequency of FISH-painted translocations
is substituted in the presented linear-quadratic equation
and a corresponding D value is derived by solving theequation.
For instance, in case 1.6 translocations per 100 cells(the frequency 0.016) were observed in an irradiatedpatient on the basis of a calibration curve, itcorresponded to the absorbed dose of 0.77 Gy (95%
confidence interval from 0.3 up to 1.10 Gy). If 5translocations per 100 cells (the frequency 0.05) wereobserved, the absorbed dose made up to 1.54 Gy.
It should be noted that this calibration curve
concerns only a part of cell translocations including
FISH-painted chromosomes (chromosomes 1, 4 and 12

Literature
1. IAEA: Technical Report series N260, «Biologicaldosimetry: chromosomal aberration analysis for dose
assessment», IAEA, Vienna, 1986, p.1-69.
2. Bender M.A., Awa A., Brooks A.L. et al. Current
status of cytogenetic procedures to detect andquantify previous exposures to radiation. Mutat.
Res. 196:103-159; 1988.
3. Shevchenko V.A., Snigiryova G.P. Analysis of
Dynamics of Chromosome Aberrations inConnection with the Problem of BiologicalDosimetry. SCOPE-RADTEST III Workshop on "Methodologies
ofDose
Reconstruction,
Epidemiology, and Sub-surface Transport", March,
27-31, 1995, Brussels-Liege, Belgium RL.08.95.
p.10.
4. Semov A. B., Iofa E. L., Akaeva E. A.,
Shevchenko V.A. Dose dependence of chromosome
aberration induction in ameliorators of the Chernobyl
accident. Radiat. Biol. Radioecol., 1994, v.34, 6,
865-871.
5. Snigiryova G.P., Shevchenko V.A. Retrospective
Biological Dosimetry by Means of Chromosome
Analysis Among Population of the Altai Region.
SCOPE-RADTEST
III
Workshopon"Methodologies
ofDose
Reconstruction,
Epidemiology, and Sub-surface Transport", March,
27-31, 1995, Brussels-Liege, Belgium RL.07.95. p.9.
6. Shevchenko V. A., Akaeva E. A., Yeliseyeva I. M. et
al. Human cytogenetic consequences of theChernobyl accident. Mut. Res., 361, 29-34, 1996.
7. Snigiryova G.P., Braselmann H., Salassidis K.,
Shevchenko V., Bauchinger M. Retrospective
biodosimetry of Chernobyl clean-up workers using
chromosome painting and conventional chromosome
analysis. J. Radiat. Biol., v. 71, 2, 119-127, 1997.
8. Shevchenko V.A., Snigiryova G.P. Cytogenetic
effects of the action of ionizing radiations on humanpopulations. In “Consequence of the Chernobyl

221

21. N.M. Oskorbin, G.I. Algazin, Y.N. Shoyphet.
Mathematical valuations of reliability of applicationof a FISH-method for reconstruction of small doses
radiating. The bulletin of the scientific program“Semipalaytinsk polygon - Altai”. 1996.
22. Directory on applied statistics. Т.1. 1989, М.,“Finansy i statistika”, page 244.
23. Brewen J.G., Preston R.J., Littlefield L.G.
Radiation-induced human chromosome aberration
yields following an accidental whole-body exposure
to 60Co γ-rays. Radiat. Res.; 49: 647-656, 1972.
24. Shevchenko V.A., Snigiryova G.P., Suskov I.I.,
Akayeva E.A., Elisova T.V., Iofa E.L. andNovitskaya N.N. Cytogenetic examination of the
population in regions subjected to the action ofionizing radiation. International Workshop on
Determination of Radiation Doses among Critical
Groups of the Population in the FSU after
Chernobyl. GSF - Forschungszentrum fur Umwelt
und Gesundheit, Munchen/Neuherberg, October 24
to 25, 1994.
25. Sevankaev A. V., Moiseenko V.V., Cyb A. F. On
possibility of application of biological dosimetry
methods to retrospective dose estimation inconnection with Chernobyl accident. The dose
estimation based on analysis of unstable
chromosome aberrations. Radiat. Biol. Radoecol.,1994, 34, 6, 782-792..
26. Buckton K.E., Brown W.M.C., Smith P.G.
Lymphocyte survival in men treated with X-rays forankylosing spondylitis. Nature; 214:470-473, 1967.
27. Leonard A., Deknudt G. and Leonard E.D.
Persistence of chromosome aberrations in an
accidentally irradiated subject. Rad. Protect.
Dosimetry; 22, 2: 55-57, 1988.
28. Goh K.O. Total-body irradiation and humanchromosomes IV. Cytogenetic follow-up studies 8
and 101/2 years after total-body irradiation. Rad.
Res.; 62:364-373, 1975.
29. Scheid W., Weber J. And Traut H. Chromosome
aberrations induced in human lymphocytes by an
X-radiation accident: results of a 4-year
postirradiation analysis. Int. J. Radiat. Biol.; 54, 3:
395-402, 1988.
30. Ramalho A.T. and Nasceimento A.C.H. The fate of137
chromosomal
aberrationsin
Cs-exposed
individuals in the Goiania radiation accident. Health
Physics; 60, 1: 67-70, 1991.
31. Ramalho A.T., Curado M.P., Natarajan A.T.
Lifespan of human lymphocytes estimated during a
six year cytogenetic follow-up of individuals
accidentally exposed in the 1987 radiologicalaccident in Brazil. Mutat. Res.; 331,1 :47-54, 1995.

Catastrophe: Human Health”, Moscow, 23-45, 1996.
9. Shevchenko V.A. Assessment of genetic risk fromexposure of human population to radiation. In“Consequence of the Chernobyl Catastrophe:
Human Health”, Moscow, 46-61, 1996.
10. Bender M.A., Gooch P.C. Persistent chromosome
aberrations in irradiated human subjects. II. Tree andone-half year investigation. Radiat. Res.; 18:389-396, 1963.
11. Bauchinger M. Quantification of low-level
radiation exposure by conventional chromosome
aberration analysis. Mut. Res.; 339:177-189, 1995.
12. Apelt F., Kolin-Gerresheim J. And Bauchinger M.
Analysis of chromosome damage and sce inlymphocytes after exposure in vivo and in vitro.
Mutat. Res.; 88: 61-72, 1981.
13. Lloyd D.C., Purrot R.J. and Reeder E.J. The
incidence of unstable chromosome aberrations inperipheral blood lymphocytes from unirradiated andoccupationally exposed people. Mut. Res.; 72:
523-532, 1980.
14. Bajerska A. and Liniecki J. The yield ofchromosomal aberrations in rabbit lymphocytes after
irradiation in vitro and vivo. Mutat. Res.; 27: 2,
271-284, 1975.
15. Buckton K.E., Langlands A.O., Smith P.G. et al.
Further studies on chromosome aberration
production after whole body irradiation in man. Int.
J . Radiat. Biol.; 19: 369-378, 1971.
16. Schmid E., Bauchinger M., Bender E et al.
Comparison of the chromosome damage and its dose
response after medical whole-body exposure to 60Co
gamma-rays and irradiation of blood in vitro. Int. J.
Radiat. Biol.; 26: 31-37, 1974.
17. Pinkel D., Straume T. and Gray J., Cytogenetic
analysis using quantitative, high-sensitivity,
fluorescence hybridization. Proc. of the Nat. Acad.
of Sciences ( USA); 83: 2934-2938, 1986.
18. Schmid E., Zitzelsberger H., Braselmann H. et al.
Radiation induced chromosome aberrations analyzed
by fluorescence in situ hybridization with a triple
combinationofcompositewholechromosome-specific DNA probes. Int. J. Radiat.
Biol.; 62: 6, 673-678, 1992.
19. Bauchinger M., Schmid E., Zitzelsberger H. et al.
Radiation-induced chromosome aberration analyzed
by two-color fluorescence in situ hybridization withcomposite whole chromosome-specific DNA probes
and a pancentromeric DNA probe. Int. J. Radiat.
Biol.; 64: 179-184, 1993.
20. Lucas J.N., Awa A., Straume T. et all. Rapid
translocation frequency analysis in humans decades
after exposure to ionizing radiation. Int. J. Radiat.
Biol.; 62: 1, 53-63, 1992.

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