CANCER INCIDENCE
AMONG NUCLEAR WORKERS IN RUSSIA BASED ON DATA FROM
THE INSTITUTE
OF PHYSICS AND POWER ENGINEERING: A PRELIMINARY ANALYSIS
Vayzer V.I.2, Suspitsin Yu.V.3, Fedorov Yu.V.3
2 Institute of Physics and Power
Engineering, Obninsk;
3 Medical Units of Obninsk
Introduction
The
study of the health status of nuclear workers has at least two
aspects:
1.
Assessment of the health status by comparing the incidence rates for
different diseases among the nuclear workers and the general population.
2.
Direct estimation of the relationship between incidence rates and
chronic and relatively low radiation doses.
The
first task requires a knowledge of the sex and age factors related
to the incidence of diseases in the study group and the general
population, as
well as demographic data about the nuclear workers. In the second case,
the
dose and the chronology of radiation exposure are needed for each
worker in
addition to the medical information (incidence rates).
For
cancers, the dose dependences of incidence rates and mortality have
been derived in terms of radiation risks for atomic bomb survivors and
for
patients exposed to radiation for therapeutic purposes [1-5]. These
estimates
of radiation risks, however, were made for relatively high doses and
dose
rates. Exclusion of high doses (more than 0.2-0.5 Sv) from the study of
cancer
incidence in the Japanese cohort leads to a significant change in the
dose
dependence of cancer incidence [6]. In this sense, the cohort of the
Chernobyl
emergency workers (average dose 0.1 Sv) is somewhat intermediate in the
estimation of radiation risks [7]. It should be noted that radiation
risks from
exposure to low doses and low dose rates are estimated using different
extrapolation methods [2], which involve significant uncertainties.
Direct
estimates of the effects of chronic low radiation doses on the
development of cancer can be obtained by studies of cancer incidence
among
workers in the nuclear industry. A study of the dose dependence of
cancer
incidence should be based on systematic specialized medical follow-up
and
dosimetric monitoring of the subjects. Such research is being carried
out in
the USA [8], Canada [9], UK [10] and other countries. To take advantage
of the
accumulated experience from these studies, international projects
involving many
countries have also been initiated [11].
Materials and methods
General
information about IPPE
Like
most workers of the nuclear industry, the IPPE personnel are
subject to annual medical examinations, the results of which are
written down
in medical records. Dosimetric monitoring of a fraction of the IPPE
workers is
conducted on a permanent basis by the radiation safety department.
The
personnel department of the IPPE maintains a database of
information about all employees. The numbers of IPPE personnel from
1986 to 1997
are shown in Figure 1. As can be seen from the figure, the number of
employees
at IPPE was almost constant (at about 10,000 persons) up to the early
1990s,
but since 1991 the number decreased sharply and is now 5,000 persons.
Fig. 1. Numbers of workers in
IPEE from
1987-1997. The squares are all IPPE workers and
circles
are those workers under individual
dosimetric monitoring.
The
method for registration of the IPPE workers with cancer is described
below. All residents of Obninsk are subject to annual primary screening
in two
clinics. This is basically a prophylactic examination and usually takes
place
when patients visit the doctors for other reasons. The IPPE workers
engaged in
hazardous activities are subject to more frequent and more thorough
examinations (by more doctors with different specialties) compared to
other
residents. If cancer is suspected, a patient is referred to the cancer
specialist to confirm the diagnosis, and, if necessary, the diagnosis
is verified
at the Medical Radiological Research Center (MRRC) in Obninsk, the
leading
Russian organization in fundamental and clinical radiobiology,
experimental
radiology, radiopharmaceutics, radiation epidemiology, radiation
diagnostics
and cancer therapy. If the diagnosis is confirmed, a specially designed
form is
completed. This form contains information on the condition of the
patient at
diagnosis, histological (X-ray, clinical, etc.) ascertainment of
diagnosis,
treatment, follow-up, etc. When a cancer patient dies, the cause of
death is
recorded and the form is placed in the archive of deceased cancer
patients of
Obninsk located in the cancer department of the city hospital. Apart
from the
specially designed forms, information about cancer patients can be
obtained
from the regular medical records stored in the registration office of
the city
hospital (medical unit N 8).
To
ensure that the database of cancer patients who were or are working
in IPPE is as accurate and as complete as possible, a special method
was
developed to check the registration of cancer patients. First, a list
of cancer
patients registered in the cancer department of the city hospital is
compiled
under the guidance of the chief oncologist of Obninsk. Those who were
registered and died and whose records were placed in the archive are
also
included in the list. These lists are then given to the IPPE personnel
department where the IPPE workers (present or former) are identified
and their
personal data are verified, in particular the date of birth,
occupation, date
of employment. When the verified lists are received, a member of the
city
hospital staff fills in a questionnaire for each patient whose
employment at
the IPPE has been confirmed. As the questionnaires accumulate, they are
given
to MRRC to be reviewed carefully to ensure quality and completeness and
then
are entered into the database. The information is first subjected to
computer
checks (syntactical and logical) and only then is it entered the
database. The
questionnaires that fail the checks are returned for additional
verification.
To date, information on 505 cancer cases among the IPPE workers is
available.
These cases were diagnosed between 1966 and 1997.
Collection of
dosimetric information
The
dosimetry unit of the IPPE has been operating since the Institute
was founded. In the past, personal dosimetric information was kept on
paper in
specialized archives along with information on radiation doses received
before
employment at the IPPE. Individual dosimetric monitoring (IDM) is
performed
centrally by the radiation safety department and consists of
measurement of
external radiation doses (from g-, X- ,b-particle
and neutron radiation sources) and
estimation of internal radiation dose. The IDM of external irradiation
covered
between 10 to 35% of the IPPE workers in different years. The annual
collective
radiation dose at the IPPE is about 4 person-Sv, and the average
individual
dose is about 2-3 mSv. The maximum individual doses do not exceed 30
mSv a
year.
Doses
of X- and g-radiation
are determined using thermoluminescent
dosimeters with tissue-equivalent filters in the energy range 50 KeV -
3 MeV
with a sensitivity of 0.01 mSv. Exposure to b-particles
is monitored with dosimeters composed of
film detectors covered by different layers of materials that simulate
the
layers of the skin. Doses of neutron radiation are determined using the
neutron
activation method. Internal radiation doses are determined using a
whole-body
counter. Exposure to uranium and transuranium radionuclides is
evaluated from
biophysical measurements.
Under
the current regulations, dosimetry data must be preserved on paper
for 70 years.
The
criterion for putting personnel under individual dosimetric
monitoring is that external irradiation has occurred at levels of more
than 2
mSv per year, or the possibility that a dose has been received above
the
established dose limit (emergencies,
accidents). For internal irradiation, the possibility of radionuclide
intake
during contact with radionuclides (hot laboratory, preventive repair of
reactors, etc.) is the guideline for using IDM. The instruments used
for IDM
are subject to annual calibration checks by State Standards
organizations.
Since
1991 individual doses have been entered into a computer, hence
linking medical and dosimetric information does not present much
difficulty.
Such linking, however, also requires working with paper documents,
which is
rather time-consuming.
It can
be seen from Figure 1 that the number of workers under IDM since
1991 has not change as greatly as the total number of the IPPE
personnel. The
collective doses for the IPPE personnel in 1991-1997 were within
3.2-5.0
person-Sv, and the mean annual doses were within 2.0-2.8 mSv.
As was
mentioned above, for the IPPE workers employed in 1991 and later,
the IDM annual data, including the retrospective data, are preserved on
both
paper and computer. Using annual individual dosimetric data, individual
cumulative doses can be estimated.
The
dose was estimated as the cumulative dose received by the time of
the completion of follow-up minus the latent period. Therefore the
doses
received during the latent period were not included in the cumulative
dose.
The
latent period was set as 10 years for solid cancers, 5 years for
thyroid
cancers and 2 years for leukemias.
It
should be noted that the contribution of internal
exposure to the total dose received by the IPPE workers under study
does not
exceed 1%, which is much lower the error in measuring the external
dose. Thus
the contribution of internal irradiation to the total dose was not
taken into
account.
Population
under study
In this
analysis, the IPPE employees of 1991-1997 are
studied. Two groups of workers can be identified:
1.
All
employees of the IPPE in the period from 1991 to
1997.
2.
The
IPPE employees of 1991-1997 covered by IDM.
For
this study the groups include only IPPE workers employed before
1981. This restriction was imposed to reduce the uncertainty associated
with
the possible latent period in developing solid cancer. We thus
minimized the
possibility of including those who already had the disease at the time
they
were employed in the study cohort.
Table 1
Characteristics
of the cohort of the IPPE employees during 1991-1997
who were hired before 1981
|
|
All workers |
Workers under IDM |
||
|
Males |
Females |
Males |
Females |
|
|
Number of persons |
3442 |
2202 |
1079 |
155 |
|
Number of cancer cases |
108 |
50 |
17 |
7 |
|
Number of person-years |
17299 |
10421 |
6210 |
890 |
|
Mean follow-up period
(years) |
5.0 |
4.7 |
5.7 |
5.7 |
|
Mean attained age at end
of follow-up (years) |
55.2 |
51.7 |
53.5 |
55.8 |
This
study was limited to those employed during the period 1991-1997
because the available computer database contains individual dosimetric
information (including retrospective data) for the IPPE workers
employed in
this period. Earlier information on doses is available only on paper.
The
characteristics of the study cohorts are presented in Table 1, which
contains
information on the distribution of the IPPE workers by sex,
person-years, mean
follow-up period, mean attained age and number of cancer cases
diagnosed. Of
the workers under IDM, seven persons with cumulative doses more than
500 mSv
were excluded from the study.
Methods of
analysis
The
person-time at risk for development of a disease of a given type was
estimated as the difference in the dates T1
and T0,
where T1 is date of the
completion of the last follow-up,
date of leaving IPPE, date of cancer diagnosis, date of death, or 1
January
1998, whichever come first. The incidence rate is defined as the ratio
of total
cases to total time at risk measured in person-years.
To
determine the differences between the cancer incidence rates of the
IPPE workers and the general population of Russia, the standardized
incidence
ratio (SIR) was estimated [13]. For this purpose, we used the age- and
sex-specific cancer incidence rates for the population of Russia
published in
[14]. That publication contains all Russian cancer incidence rates for
both
sexes with 5-year age intervals for cancers of the most frequent sites,
based
on information supplied by regional cancer dispensaries and specialized
cancer
clinics. These data are the official statistics on cancer incidence in
Russia.
To
study the dose dependence of the incidence rate, the data
for the individual IPPE workers were grouped. The data in the present
analysis were
split in 10 strata by attained age (15-20, 20-25, 30-35, 35-40, 40-45,
45-50,
50-55, 55-60, 60+ years), 3 groups by dose (0-25, 25-50, 50+ mSv) and 2
groups
by sex.
Let i be the index of the sex-age group and j be the index of the
dose group. Yji is number
of cases, Pij are
person-years, Mij is the
incidence rate in stratum ij.
Mij
for a given class of diseases can be determined as follows:
Mij
=
Yij / Pij
.
(1)
It
seems reasonable to assume [13, 15] that the values of Yij
are independent random values with a Poisson distribution and the
mathematical
formulation E(Yij) = PijMij.
To determine
the dose dependence of Mij,
Mij should be
presented as a parametric function with its parameters determined from
the
maximization of the likelihood function:
L
= S
{Yij ln(PijMij)
- PijMij},
(2)
where Mij
= f(Dij), where Dij
is the mean dose in
stratum ij. In this work we used a
simple function:
f(Dij)
= Mi0 (1
+ bDij).
(3)
Equation
(3) is used to determine the significance of the dose dependence of the
relative risk. As a statistical test we used the test of the ratio of
likelihood maxima at zero hypothesis b=0. The
background dose group (j=0) was the
group 0-25
mSv.
Estimation
of the parameters of equation (3), statistical tests and the
determination of confidence levels were carried out using the software
program
AMFIT [15].
Results
In the
period from 1991 to 1997, a total of 158 cancer cases
were detected among the IPPE workers in the study cohorts; 24 of these
workers
were under IDM. Table 2 shows the distribution of cancer incidence for
the
study groups. Figures 2 and 3 show the distribution of the IPPE workers
by
attained age for all those employed 10 years or more (i.e. hired prior
to 1981)
working in IPPE from 1991 to 1997 and covered by IDM during this period.
Table 3
compares the cancer incidence rates of the IPPE
workers and the general population of Russia. The SIRs for IPPE workers
in
1991-1997 are presented by individual year in Figure 4. For persons
under IDM,
the number of cancer cases was too small to calculate SIRs by year. The
SIRs
for the total study period for these persons were 0.42 (0.24, 0.67) for
males
and 1.41 (0.56, 2.90) for females.
To
estimate a possible dependence of the cancer incidence
rate on cumulative dose, the distribution of which is shown in Figure
5, with
mean values given in Table 4, the excess relative risk was derived [3].
The
excess relative risk per 1 Gy for all cancers was 0.91 (-2.75, 4.61 95%
CI) for
males and 0.40 (-6.94, 7.83 95% CI) for females. These estimates,
however,
should be treated as preliminary, because the number of cases
considered in the
analysis of the dose-response relationship was small (17 males and 7
females).
Table 2
Cancer incidence among the workers at IPEE
|
ICD-9 |
All |
With IDM |
|||
|
Males |
Females |
Males |
Females |
||
|
Oral cavity |
140-149 |
6 |
0 |
1 |
0 |
|
Esophagus |
150 |
1 |
0 |
0 |
0 |
|
Stomach |
151 |
16 |
2 |
2 |
0 |
|
Colon |
153 |
4 |
4 |
2 |
0 |
|
Rectum |
154 |
7 |
1 |
3 |
0 |
|
Gallbladder |
156 |
1 |
0 |
0 |
0 |
|
Pancreas |
157 |
2 |
1 |
0 |
0 |
|
Larynx |
161 |
2 |
0 |
0 |
0 |
|
Trachea, bronchus, lung |
162 |
18 |
1 |
0 |
0 |
|
Bones and articular
cartilages |
170 |
1 |
0 |
0 |
0 |
|
Connective and other soft
tissues |
171 |
2 |
1 |
0 |
0 |
|
Melanoma of skin |
172 |
4 |
1 |
1 |
0 |
|
Other malignant neoplasms
of skin |
173 |
17 |
5 |
2 |
0 |
|
Breast |
174 |
- |
15 |
0 |
4 |
|
Cervix uteri |
180 |
- |
1 |
0 |
0 |
|
Corpus uteri |
182 |
- |
8 |
0 |
3 |
|
Ovaries |
183 |
- |
2 |
0 |
0 |
|
Other malignant neoplasms
of female genital organs |
184 |
- |
1 |
0 |
0 |
|
Prostate |
185 |
4 |
- |
0 |
0 |
|
Bladder |
188 |
6 |
1 |
3 |
0 |
|
Kidney |
189.0 |
6 |
0 |
1 |
0 |
|
Renal pelvis |
189.1 |
2 |
0 |
- |
- |
|
Unspecified localization
of uropoietic organs |
189.9 |
3 |
0 |
- |
- |
|
Eye |
190 |
0 |
1 |
0 |
0 |
|
Nervous system |
191 |
1 |
0 |
0 |
0 |
|
Thyroid |
193 |
0 |
2 |
0 |
0 |
|
Unspecified localization |
199 |
0 |
1 |
0 |
0 |
|
Lymphosarcoma and
reticulosarcoma |
200 |
1 |
1 |
0 |
0 |
|
Hodgkin’s disease |
201 |
1 |
0 |
0 |
- |
|
Multiple myeloma |
203 |
1 |
0 |
1 |
- |
|
Chronic lymphoid leukemia |
204.1 |
1 |
0 |
0 |
- |
|
Myeloid leukemia |
205.1 |
1 |
1 |
1 |
- |
|
All cancers |
140-208 |
108 |
50 |
17 |
7 |
Fig. 2. Distribution, by attained
age, of
the cohort of the IPPE employees of 1991-1997.
Fig. 3. Distribution, by attained age, of the cohort of those IPPE
employees
of 1991-1997
under individual dosimentic monitoring.
Table 3
Number
of cases and
SIR for some classes of cancers diagnosed among the IPPE workers
|
Cancer site |
ICD-9 |
Number of cases |
SIR |
||
|
Males |
Females |
Males |
Females |
||
|
All cancers |
140-208 |
108 |
50 |
0.93 (0.76, 1.12)a |
1.42 (1.06, 1.87) |
|
Digestive organs |
150-159 |
31 |
8 |
0.83 (0.56, 1.18) |
1.01 (0.44, 1.98) |
|
Stomach |
151 |
16 |
2 |
0.93 (0.53, 1.50) |
0.68 (0.08, 2.36) |
|
Respiratory and thoracic
organs |
160-165 |
20 |
1 |
0.50 (0.31, 0.78) |
0.69 (0.01, 3.38) |
|
Trachea, bronchus, lung |
162 |
18 |
1 |
0.52 (0.31, 0.82) |
0.74 (0.9, 3.66) |
|
Bones, connective tissue,
skin and breast |
170-175 |
24 |
22 |
2.53 (1.62, 3.76) |
1.73 (1.08, 2.62) |
|
Skin |
172-173 |
21 |
6 |
2.53 (1.57, 3.86) |
1.65 (0.60, 3.56) |
|
Melanoma skin |
172 |
4 |
1 |
3.94 (1.06, 9.96) |
1.65 (0.02, 8.1) |
|
Breast |
174 |
- |
15 |
- |
1.72 (0.96, 2.84) |
|
Genitourinary organs |
179-189 |
21 |
13 |
1.79 (1.11, 2.73) |
3.81 (2.03, 6.5) |
|
Corpus uteri |
182 |
- |
8 |
- |
3.11 (1.34, 6.11) |
|
Prostate |
185 |
4 |
- |
1.2 (0.3, 3.0) |
- |
|
Bladder |
188 |
6 |
1 |
1.4 (0.5, 3.0) |
3.95 (0.05, 19.5) |
|
Kidney, renal pelvis,
unspecified localization of uropoietic organs |
189.0, 189.1, 189.9 |
11 |
0 |
2.97 (1.48, 5.30) |
0 |
a The 95% confidence levels
are given in parentheses.
Fig. 4. SIRs for all cancers for
the IPPE
workers in 1991-1997.
Fig. 5. Distribution of the
cohort of the
IPPE workers in 1991-1997
by cumulative external radiation dose.
Table 4
Mean
cumulative external radiation doses in the cohort of the IPPE workers
in
1991-1997
|
|
All |
Males |
Females |
|
Mean dose for cancer
patients (mSv) |
105 |
123 |
62 |
|
Mean dose for healthy
people (mSv) |
69 |
74 |
35 |
|
Mean dose for all persons
(mSv) |
70 |
75 |
37 |
The
values of the excess relative risk per unit dose were
positive, even though they were not statistically significant, and
therefore
the question of the dose dependence of the cancer incidence remains
open and
requires further study.
Discussion
The
effect of low-doses and low-dose-rate irradiation on human health
has not been studied thoroughly in Russia until recently, although many
people
are exposed to such levels. A study of the health consequences of low
radiation
doses should rely on either the experience of other studies or the
direct
long-term follow-up of the exposed population, including medical and
dosimetric
monitoring. The last requirement is satisfied by workers in the nuclear
industry, since these workers are under individual dosimetric
monitoring and
are subject to regular medical examination as part of their
occupational safety
programs. The application of results from other studies of radiation
effects on
human health is problematic because of the paucity of studies on low
doses and
dose rates. At the same time, if the conclusions from the studies of
the
relationship between high doses and incidence of diseases, especially
cancers,
are used, the models have to be extrapolated [2] to the region of low
doses,
which results in considerable uncertainties.
In the
present work, the study population was the staff of
the Institute of Physics and Power Engineering located in Obninsk,
Russia. The
cancer incidence among the IPPE personnel employed during 1991-1997 and
recruited before 1981 was studied. The selection of 1991 as the
starting year
for our study was made because the computerized database contains
dosimetry
information starting from 1991. Prior to 1991, dosimetric information
was
recorded on paper and is stored in archives. The restriction of the
study to
workers employed before 1981 was done to reduce the possibility of
including
persons with a pre-existing cancer. With the study exclusions in mind,
158
cancer cases were studied; of those 24 cases were persons under
individual
dosimetric monitoring. Due to the indicated constraints and the limited
number
of cases, the results of the analysis should be considered preliminary.
The
cancer incidence rates for the IPPE workers compared to the general
population of Russia are statistically significantly higher for all
cancers for
females (SIR=1.42 (1.06, 1.87)); for cancers of the bone, connective
tissues
and skin for males (SIR=2.53 (1.62, 3.76)); for cancers of the bone,
connective
tissues, skin and breast for females (SIR=1.73 (1.08, 2.62)); and for
cancers
of the genitourinary organs both males (SIR=1.79 (1.11, 2.73)) and
females
(SIR=3.81 (2.03, 6.5)). No statistically significant difference of the
SIR from
unity was found for the other cancer classes due to the limited number
of
cases.
The
finding of a statistically significant excess in the
incidence rate for some cancer sites among the IPPE personnel compared
to the
general Russian population was unexpected and is not consistent with
the
well-known phenomenon referred to as the healthy worker effect when
applied to
nuclear workers. This can possibly be explained both by technological
factors
and by the fact that the nuclear industry in Obninsk was and is the
main
industry. As a result, the level of health care for the residents, many
of whom
work at nuclear facilities, is better than in Russia on average.
Evidence for
this can be found by comparing the estimates of cancer SIR for the IPPE
workers
with that for residents of Obninsk (Table 5). The population of Obninsk
in the
period considered was about 107 thousand people. The mean age in 1991
was 31.5
years for men and 35.1 years for women. As is seen from Table 5, the
SIR values
for the nuclear workers and the residents of Obninsk are comparable
within
statistical errors. The similarity in the cancer incidence rates for
IPPE
workers and the Obninsk population suggests that the people in Obninsk
received
good medical care and that the differences between the nuclear workers
and the
Russian rates are not radiation-associated effects, but rather are due
to
better registration of diseases among Obninsk residents. On the other
hand, it
should be remembered that many residents of Obninsk worked for a long
time at
other facilities of the nuclear industry of Russia.
Table 5
Results
of SIR
analysis of cancer incidence rates in IPPE (1991-1997) and
in Obninsk population (1992-1997) (control)
|
ICD-9 |
Obninsk |
IPPE |
||
|
Males |
Females |
Males |
Females |
|
|
140-208 |
1.20 (1.12, 1.28)a |
1.58 (1.49, 1.69) |
0.93 (0.76, 1.12) |
1.42 (1.06, 1.87) |
|
170-175 |
2.20 (1.86, 2.60) |
1.78 (1.60, 1.97) |
2.53 (1.62, 3.76) |
1.73 (1.08, 2.62) |
|
179-189 |
1.39 (1.14, 1.69) |
3.41 (2.93, 3.93) |
1.79 (1.11, 2.73) |
3.81 (2.03, 6.5) |
a The 95% confidence levels
are
indicated in parentheses.
The
study of the dose dependence of the cancer incidence
rates revealed a lack of robustness in the estimates of relative risk;
the
linear trend of the relative risk dependence is positive, but the
estimates of
excess relative risk are not statistically significant, which is most
probably
associated with the small number of cancer cases and the small size of
the
cohort under study (person-years). Extending the size of the cohort of
the IPPE
workers under IDM by including those who left the Institute before 1991
would
probably allow more definitive conclusions to be drawn about the value
of
radiation risks.
Conclusions
Based
on the analysis of the data for the IPPE workers, including their
medical and dosimetric information, the cancer incidence rates in the
IPPE
workers and the general population of Russia were compared and
preliminary
conclusions are drawn about the dose dependence of incidence rates for
malignant neoplasms.
As a
whole, a statistically significant excess of cancer incidence among
the IPPE personnel compared to the general population of Russia was
found for
all cancers (females); for bone, connective tissue, skin (males and
females)
and breast (females); and for genitourinary organs (males and females).
The
highest excess was found for skin cancer (males). The result for skin
is most
likely due to ascertainment or treatment bias rather than to radiation.
Cancer
incidence at these sites was also significantly elevated in the general
population
of Obninsk compared to the rates for the general population of Russia,
suggesting that the increased incidence observed for the IPPE workers
may be
due to better diagnosis and registration of cancer in the city of
Obninsk.
Estimates
of the excess relative risk per unit dose in the study of the
dose dependence of the cancer incidence rate were positive but not
statistically significant. The excess relative risk per 1 Gy for all
cancers
was 0.91 (-2.75, 4.61 95% CI) for males and 0.40 (-6.94, 7.83 95% CI)
for
females. The absence of statistical significance may be due to the
limited
number of cases studied.
These
estimates
should be considered to be preliminary, as the number of cases included
in the
analysis of dose response is too small (17 males and 7 females) to
perform an
adequate analysis of the dose response.
The
similarity in the cancer incidence rates for IPPE workers and the
Obninsk population suggests that people in Obninsk received good
medical care
and that the differences between the nuclear workers and the rates for
the
general population of Russia are not associated with radiation, but
rather due
to better registration of diseases among the residents of Obninsk.
Our
study is one of the few attempts to understand the effects of
radiation on the health of nuclear workers in Russia. The results
should be
treated as preliminary and they require further refinement. An increase
in the
size of the study cohort and an extension of the follow-up period would
allow a
reduction of the uncertainties involved in the analysis.
Acknowledgments
References
[1]
National
Research Council, Committee on the Biological
Effects of Ionizing Radiation. Health
Effects on Populations of Exposure to Low Levels of Ionizing Radiation
(BEIR V).
- Washington, DC: National Academy Press, 1990.
[2]
ICRP. Recommendations
of International Commission on Radiological Protection. Report 60,
International Commission on Radiological Protection. - Oxford:
Pergamon
Press, 1991.
[3]
UNSCEAR.
Sources
and Effects of Ionizing Radiation. - New York: United Nations, 1994.
[4]
Thompson
D.E., Mabuchi K., Ron E., Soda M., Tokunaga
M., Ochikubo S., Sugimoto S., Ikeda T., Terasaki M., Izumi S., Preston
D.L. Cancer incidence in atomic bomb survivors.
Part II: Solid tumors, 1958-1987.
Radiat. Res. - 1994. - V. 137. - P. S17-S67.
[5]
Pierce
D.A., Shimizu Y., Preston D.L., Vaeth M.,
Mabuchi K. Studies of the mortality of
atomic bomb survivors. Report 12, Part I. Cancer: 1950-1990.
Radiat. Res. -
1996. - V. 146. - P. 1-27.
[6]
Preston
D.L. Low
dose radiation and human health: risk estimates. In: Proceedings of
a
Conference “Low Doses of Ionizing Radiation: Biological Effects and
Regulatory
Control”. - Spain, 1997. - P. 217-229.
[7]
Ivanov
V.K., Rastopchin E.M., Gorsky A.I., Ryvkin V.B. Cancer
incidence among liquidators of the
Chernobyl accident: solid tumors, 1986-1995.
Health Phys. - 1998. - V. 74, No 3. - P. 309-314.
[8]
Gilbert
E.S., Cragle D.L., Wiggs
L.D. Updated analysis of combined
mortality data for workers at the Hanford Site, Oak Ridge National
Laboratory
and Rocky Flats Nuclear Weapons Plant.
Radiat. Res. - 1993. - V. 136. - P. 408-421.
[9]
Gribbin
M.A., Weeks J.L., Howe
G.R. Cancer mortality (1956-1985) among
male employees of atomic energy of Canada limited with respect to
occupational
exposure to external low-linear-energy-transfer ionizing radiation.
Radiat.
Res. - 1993. - V. 133. - P. 375-380.
[10]
Carpenter
L., Higgins C., Douglas A., Fraser P., Beral
V., Smith P. Combined analysis of
mortality in the three United Kingdom Nuclear industry workforces,
1946-1988. Radiat. Res. - 1994. - V.
138. - P. 224-238.
[11]
Cardis
E., Gilbert E.S., Carpenter L., Howe G., Kato
I., Armstrong B. K., Beral V., Cowper G., Douglas A., Fix J., Fry S.A.,
Kaldor
J., Lave C., Salmon L., Smith P.G., Voelz G.L., Wiggs L.D. Effects
of low doses and low doses rates of external ionizing
radiation: Cancer mortality among nuclear workers in three countries.
Radiat. Res. - 1995. - V. 143. - P. 117-132.
[12]
Koshurnikova
N.A., Bolotnikova N.G., Grusdeva E.A.,
Kobirova N.R., Kreslov V.V., Okatenko P.F., Romanov S.A., Filippova
L.G.,
Khokhrryakov V.F., Shilnikova N.S. Late
effects of occupational radiation exposure (mortality in personal of
“Mayak”
complex for 45 years of follow-up). Radiation and Risk (Bulletin of
the
National Radiation and Epidemiological Registry). - 1995. - Issue 5. -
P.
137-144 (in Russian).
[13]
Breslow
N.E., Day N.E. Statistical Methods in Cancer Research. Vol
II. The Design and Analysis
of Cohort Studies. Scientific Publication 82. - Lyon: International
Agency
for Research on Cancer, 1987.
[14]
Incidence
of Malignant Neoplasms and Mortality from them
among the Population of Russia in 1993-1996
(V.I.Chissov, V.V.Starinsky and
L.V.Remmenik, Eds.). - Moscow: Gertsen Research Cancer Institute, 1998
(in
Russian).
[15]
Preston
D.L., Lubin J.H., Pierce D.A. EPICURE User's Guide. -
Seattle:
Hirosoft International Corp., 1992.
[16]
WHO International
Classification of Diseases, 9th Revision. - Geneva: WHO, 1977.