"Radiation & Risk", 2003, special issue
2. PREDICTION OF RADIATION-INDUCED THYROID CANCERS AMONG RESIDENTS
OF THE ORYOL OBLAST BASED ON THE ICRP MODELS
2.1. Model of radiation risks for thyroid cancer
Let us first define the terminology used here before describing the model for the radiation risk. A risk of
disease (death) is understood as a probability m of developing disease by an individual during a given time
interval. The risk or probability of developing disease depends on age, sex, profession, lifestyle, place of
residence, time and other factors. By way of an example, let us consider a group of N persons not exposed to
radiation, followed up for a year with a view to determine how many cases occurred in this group. If during a year
E of persons (expected number of cases) developed a disease in this group, then the risk over a year will be
estimated as
m = E/N (the risk m is called spontaneous or background). Given N = 100 thousand people, then m is to the
spontaneous incidence rate per 100 thousand persons. If the group was exposed to radiation, then the number of
cases will change and be equal to O (observed number of cases). In absolute terms, the effect of exposure is
characterized by the excess absolute risk EAR=O-E. The relative significance of exposure is described by EER excess relative risk.
ERR = EAR/E = (O-E) /E.
(2.1)
One of the key characteristics of the level of radiation-induced diseases is the attributive risk ATR
(sometimes called the probability of causation POC or simply PC ) defined as:
ATR 
ERR
.
1  ERR
(2.2)
The attributive risk is the ratio of radiation-induced diseases to the number of all diseases. The attributive
risk is often expressed in percent. The excess absolute risk EAR is calculated as:
EAR  m  ERR ,
(2.3)
where m is the background incidence rate.
In this work the model of excess absolute risk BEIR-V [1] recommended by the ICRP is used for calculating
thyroid cancer:
EAR  2.5  10 4  D  F  S  G ,
(2.4)
where F is the efficiency factor (for isotopes 125I, 131I F = 1/3, for other iodine isotopes F = 1); the sex factor
S = 2/3 for males and S = 4/3 for females; the age factor G = 1 at g  18 and G = 0.5 at g > 18. The latent period
is taken to be TL = 5 years.
The calculation of radiation-induced risks requires a knowledge of the background incidence rates. We use
the average Russian incidence rates for 1996 [2] given in Table 2.1 for the background rates. For comparison the
table contains general cancer incidence rates. As can be seen, thyroid cancer is a fairly rare disease. Thyroid
cancer makes, on average, only a few percent of all cancers. This section describes a model of radiation risks of
thyroid cancer. This disease occurs 2-3 times more frequently in females than in males. In the subsequent
chapter there is a projection of radiation risks of this disease for residents of the Oryol oblast.
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"Radiation & Risk", 2003, special issue
Table 2.1. Background incidence and death rates in 1996.
Age interval
0- 4
5- 9
10 - 14
15 - 19
20 - 24
25 - 29
30 - 34
35 - 39
40 - 44
45 - 49
50 - 54
55 - 59
60 - 64
65 - 69
70 - 74
>74
Incidence rate per 100 thousand persons
All Cancer
Thyroid Caner
males
females
males
females
12
11
0.00
0.00
11
8
0.04
0.09
10
8
0.13
0.40
16
14
0.25
0.91
20
24
0.30
2.0
23
37
0.59
2.8
36
67
0.74
4.5
64
114
0.89
5.9
136
194
1.2
8.7
289
314
2.3
11.6
543
421
3.4
13.0
804
480
2.8
10.8
1175
632
3.6
10.7
1539
755
3.8
10.1
1974
944
5.4
9.5
1814
856
3.6
7.1
Death rate per 1 thousand from
all causes
males
4.45
0.61
0.58
2.14
4.12
4.96
6.57
8.56
12.0
16.8
23.3
30.5
41.3
55.6
71.0
138.0
females
3.33
0.37
0.33
0.80
0.98
1.22
1.57
2.24
3.32
5.09
7.46
10.5
15.9
24.5
39.0
106.
2.2. Demographic data and doses for the population of the Oryol oblast
The depositions from the Chernobyl accident resulted in radioactive contamination of the territories of the
Bryansk, Kaluga, Lipetsk, Oryol, Ryazan and Tula oblasts. Starting from the moment of contamination the
population of these territories was exposed to internal and external irradiation from a mix of a variety of fission
products and activation products. The main exposure source were radioisotopes of iodine, cesium, strontium and
plutonium. So far, mean thyroid doses have been calculated for residents of the indicated oblasts. Table 2.2
includes data on accumulated doses and populations of the rayons of the Oryol oblast. As of 1986 the general
population of the oblast was 887 thousand people (of them 190 thousand children and 697 thousand adults).
Table 2.2. Populations of rayons of the Oryol oblast and the accumulated doses averaged over each rayon.
Population
Administrative name
BOLKHOVSKY
VERKHOVSKY
GLAZUNOVSKY
DMITROVSKY
DOLZHANSKY
ZALEGOSHENSKY
ZNAMENSKY
KOLPNYANSKY
KORSAKOVSKY
KRASNOZORENSKY
KROMSKY
LIVENSKY
MALOARKHANGELSKY
MTSENSKY
NOVODEREVENKOVSKY
NOVOSILSKY
ORLOVSKY
POKROVSKY
SVERDLOVSKY
SOSKOVSKY
TROSNYANSKY
URITSKY
KHOTYNETSKY
SHABLYKINSKY
TOTAL OBLAST
children
adults
total
5339
5479
3728
4262
3480
4156
1438
5014
1129
2101
5524
18031
3476
14778
3276
2661
82741
4443
4317
2027
3140
4219
2896
2426
190095
19586
20103
13677
15636
12768
15248
5277
18395
4143
7707
20266
66153
12755
54219
12021
9764
303552
16303
15841
7437
11521
15481
10627
8903
697393
24925
25582
17405
19898
16248
19404
6715
23409
5272
9808
25790
84184
16231
68997
15297
12425
386293
20746
20158
9464
14661
19700
13523
11329
887488
18
Accumulated
thyroid dose
(adults), mGy
17.1
8.59
14.3
21
5.29
9.03
8.97
7.73
10.5
12.4
14.8
5.8
22
8.05
9.08
10.5
9
10.3
14.4
12.8
15.9
10.8
6.73
10.5
13
Accumulated
thyroid dose
(children), mGy
71.4
28.4
49.5
84.3
16.3
31
27.3
24.6
36.7
35.4
54.6
21
66.1
32.2
29.4
36.7
40.6
31.3
48
37
48.9
38.3
21.6
34
38.7
"Radiation & Risk", 2003, special issue
As a result of the intense rainfall on 28-29 April 1986 the territory of the Oryol oblast was contaminated by
radioactivity. The rayons worst affected were Bolkhovsky, Dmitrovsky, Kromsky and Maloarkhangelsky rayons.
The accumulated doses in children of these rayons exceed 50 mGy and the doses in adults are up to 22 mGy.
Figures 1.15 and 1.16 of chapter 1 present the maps of the Oryol oblast with mean accumulated doses (iodine) in
mGy in children and adults of the studied rayons, respectively.
In adults the accumulated thyroid doses are about 3-4 times lower than those in children. As a
consequence, the risk of radiation-induced thyroid cancers is estimated to be 6-8 times higher in children than in
adults (for children the factor G=1 for adults G=0.5).
2.3. Mathematical model for predicting radiation-induced risks
In a general case, the dynamics of cancer incidence in the population with uniform doses is described by a
system of differential equations with partial derivatives written as:
 n n

    n   mi  mi   n   hi  ni  ni   Q u , t 
t  u
ni ni

 mi  n   i  ni  hi  ni
t
u
ni ni

 mi  n   i  ni  hi  ni
t
u
(2.5)
Here n is the number of healthy individuals, ni is the number of patients with the background i-th disease,
ni is the number of patients with radiation-induced i-th disease,  is the background death rate, hi is the survival
rate for the i-th disease, i is the death rate from the i-th disease, Q accounts for birth rate and migration process.
The background coefficients in equation (2.5) depend on time t and age u. The radiation-induced coefficients are
a function of radiation dose and other parameters. If the number of diseases is k (1  I  k), then the total number
of equations equals to 2k + 1. Taking into account the dependence of the equation parameters on sex, the
number of equations is doubled.
If the dose is not uniform over the population, for each dose interval a system of equations similar to
system (2.5) is written. At the initial time moment the distribution of population by age n(u,o) is specified.
Assuming the maximum age um, n(u,t)=0 at u > um (further in calculations um = 90 years).
Considering the uncertainty in the demographic and epidemiological data over the years since the accident
and in projections, the prognostic model was based on the following assumptions. It is assumed that the
accumulated radiation dose (iodine) was received only by the population living in the Oryol oblast in 1986. Thus,
at a starting time moment the distribution n(u,s,0) of the population of each rayon by age u and sex s are
considered to be known. As n(u,s,0) we take the age distribution of the population of the whole Oryol oblast
normalized to the number of residents in a particular rayon. The changes in population as a result of background
deaths from all causes at t>0 (with allowance for sex) is described by the equation:
n u , s , t  n u , s , t 

   u , s   n u , s , t  ,
t
u
(2.6)
where (u,s) is the death factor dependent only on age and sex. For brevity the sex parameter s is omitted. In the
calculations the mean Russian death rates for 1996 shown in Table 2.1 are used.
To elucidate the influence of uncertainties in demographic data on prediction results we used
“standardized” age distribution of population derived from the solution of the following equation:
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"Radiation & Risk", 2003, special issue
dn ( u )
   ( u )  n( u )
du
(2.7)
at the initial condition n(0)=n0. This distribution (for each sex) was normalized to the number of residents of a
given rayon. Figure 2.1 presents both age distributions of the population for the whole Oryol oblast.
Fig. 2.1. Age distribution of the population of the Oryol oblast.
The solid line is the standardized distribution calculated with equation (2.7).
The incidence rate for the i-th background disease (number of cases per year) for a given age at the time
moment t>TL was calculated as follows:
ni ( u , t )  mi ( u )  n( u , t ) ,
(2.8)
where mi(u) is the coefficient of the i-th incidence rate. The incidence rates are shown in Table 2.1.
The incidence rate ni of radiation-induced diseases at a given age at the time moment t was calculated by
the equation:
ni ( u ,t )  EARi ( u , g ,t , D )  n( u ,t ) .
(2.9)
The cumulative number of background Ni and radiation-induced Ni diseases at the time moment t>TL is
found as follows:
um
t
Ni ( t )   d  ni ( u , )du ,
(2.10)

TL
t
um
Ni ( t )   d  ni ( u , )du .
TL
(2.11)

Corresponding lifetime risks are determined as Ni(um) and Ni(um) (i.e. the number of cases over the whole
time of the cohort existence).
Equation (2.6) was solved by the numerical method with the step of time and age integration of 1 year.
Accordingly, the number of background and radiation-induced cases were calculated for each year.
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"Radiation & Risk", 2003, special issue
2.4. Information and reference software PUBRASS-2002
For calculating and predicting background and radiation-induced cancers in the residents of the Oryol
oblast an information and reference software program PUBRASS-2002 (Public Risk ASSessment) has been
developed. The size of this software is 1.8 Mb (execution module) and 0.5 Mb are the service files. The software
is based on a mathematical model for predicting cancer risks described in the previous section. The software is
written in the algorithmic language FORTRAN-90, the environment is Fortran Power Station 4.0. Figure 2.2 shows
a part of the main window of the PUBRASS software with the main menu of 4 items (RISKS, CALCULATION
RESULTS, INPUT DATA AND REFERENCES).
Fig. 2.2. Fragment of the display window of software PUBRASS-2002
with the main menu.
Each item of the main menu contains a pull-down menu, as shown in Fig. 2.3. When the first item of the
menu is activated, a dialogue window shows up and a user can select a rayon of the Oryol oblast or the whole
oblast, type of cancer, age distribution, sex and age interval at the time of exposure. Among other things, a button
“REFERENCES” is available in the dialogue window for obtaining explanatory information. The dialogue window
is shown in Fig. 2.4.
Fig. 2.3. Fragment of the main window of software PUBRASS-2002
with pull-down menus.
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"Radiation & Risk", 2003, special issue
Fig. 2.4. Dialogue window for input of source data for calculating risks
for residents of the Oryol oblast.
Results of the calculation and the prediction of cancer risks are presented as time functions of risks and
maps of the Oryol oblast with indication of cumulative risks (lifetime and current year values). Figure 2.5 presents
a fragment of the screen display with the results of predicted incidence (number of persons) plotted. The plot is
accompanied by brief information about the time dependence of risk. The second item of the menu “RESULTS
OF CALCULATION” provides an opportunity to look at risks of interest. Activating the submenu “MAPPED
RISKS” the user can select a map with risks of interest (background and radiation-induced). This window is
shown in Fig. 2.6.
Fig. 2.5. Part of screen with the plot of predicted cases.
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"Radiation & Risk", 2003, special issue
The third item of the main menu “INPUT DATA” makes it possible to look at demographic and
epidemiological data used in calculations. Demographic data and information about accumulated doses (cesium
and iodine) are also presented as maps.
The forth item of the main menu “REFERENCES” provides an opportunity to read a detailed description of
software, its developer etc. It also contains a list of opened windows. Moreover, displayed information can be
copied to the exchange buffer. For doing this, after activation of the item “HIGHLIGHT GRAPHICS” a part of the
screen (plot of map) should be highlighted with a cursor. After copying the buffer content can be transferred to
another document or graphic editor (the figure copied to the buffer has the format “bmp”).
Fig. 2.6. Dialogue window to select risk maps for residents of the Oryol oblast.
The software PUBRASS can be used for calculating individual risks. Suppose a background and radiationinduced risk need to be determined for a person who received a dose at the age of 30 years. In this case the ageat-exposure interval of 30-30 should be specified.
2.5. Prediction of radiation-induced thyroid cancers in the population
of the Oryol oblast
The section presents results of the calculations and prediction of background and radiation-induced thyroid
cancers among residents of the Oryol oblast. All calculations were made using the software PUBRASS. We would
like to stress again that all risks were calculated for people living in 1986 in the Oryol oblast. Those born after
1986 are not included in the projections. It was assumed that accumulated doses were received on the very same
year. This must be true for the short-lived iodine. Calculations were made separately for children (0-14 years old
in 1986) and adults (15 years of age and older in 1986). The changes in the whole exposed population over time
are shown in Fig. 2.7 by a solid curve, and the dash line shows the number of exposed people who were under
age 15 in 1986. The general population declines with time almost linearly, while the number of people in the age
group less than 15 years of age starts decreasing significantly only 30 years after the accident.
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"Radiation & Risk", 2003, special issue
Fig. 2.7. Changes in the exposed population of the Oryol oblast over time.
The broken line - population under age 15 in 1986.
As was mentioned, thyroid cancer is a rare disease. The mean Russian incidence rate in 1996 is 3-4 cases
a year per 100 thousand people. For children this rate is less than 0.5 cases each year are 100,000 children. In
the Oryol oblast the same year the crude incidence rate was 14 cases a year per 100 thousand people.
2.5.1. Incidence in children
Figure 2.8 shows the changes with time of background (spontaneous) thyroid cancers in the population of
the Oryol oblast in those less than 15 years of age (children) in 1986.
Fig. 2.8. Time changes in the number of background (spontaneous) thyroid cancers in the population
of the Oryol oblast among those less than 15 years of age (children) in 1986.
24
"Radiation & Risk", 2003, special issue
As can be seen from the figure, some 3 cases of background diseases are predicted to occur in the current
year in this age group (this group includes people from 16 to 30 years old in the current year 2002). Since the
group consists of children, for whom the background incidence is low, the number of cases in the first 10-15 years
is low. Then the group ages and the incidence increases over time. Finally, the size of the group decreases
rapidly as a result of mortality and the number of cases decreases accordingly.
Figure 2.9 shows the time dependence of the cumulative (accumulated from 1992) number of thyroid
cancer cases among persons who were under 15 years of age in 1986. It can be seen that the total number of
thyroid cancer cases over the whole time of the existence of this group will be 500 cases. In the same figure the
cumulative number of radiation-induced thyroid cancers is shown by the broken line. The lifetime number of
radiation-induced cancers in this group is predicted to be 37 cases. Accordingly, the lifetime attributive risk will be
about 7%.
Fig. 2.9. The same as in Fig. 2.8, but for cumulative number of cases starting from
1992 (excluding the latent period of 5 years). The broken line shows the cumulative
number of radiation-induced thyroid cancers.
The attributive risk accounts for the ratio of the number of radiation-induced cancers to the entire number
of cases as percentage and is independent of parameters such as background incidence rate and size of studied
population group. The time dependence of the attributive risk for residents of the Oryol oblast (children) is
presented in Fig. 2.10. In the first years after the latent period, as follows from the figure, high values of attributive
risk above 40% are observed. This value suggests that about half of all cases are radiation induced. In 2002 the
attributive risk is about 18% (of 5 cases one is radiation induced). Starting from 2015 the attributive risk varies
between 3% and 6%.
Figures 2.11 and 2.12 show maps of the cumulative numbers of background and radiation-induced thyroid
cancers among residents of the Oryol oblast as of 2002. In the Dmitrovsky rayon which was the worst
contaminated (accumulated dose 84 mGy), according to estimates, as of 2002 there will be 0.3 background cases
and 0.3 radiation-induced cases. In the most heavily populated Oryol rayon (dose of 40.6 mGy) the number of
background cases is 5.8 and the number of calculated radiation-induced cases is 2.8.
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"Radiation & Risk", 2003, special issue
Fig. 2.10. The time change of the attributive risk of thyroid cancer for residents
of the Oryol oblast under age 15 in 1986 (children).
Fig. 2.11. Map of cumulative background (spontaneous) thyroid cancer cases in the rayons
of the Oryol oblast as of 2002 (children).
26
"Radiation & Risk", 2003, special issue
Fig. 2.12. Map of cumulative radiation-induced thyroid cancers among children in the rayons
of the Oryol oblast as of 2002.
The cumulative attributive risks of thyroid cancer as of 2002 in persons under age 15 in 1986 appear to be
quite high. On the average, in the Oryol oblast the attributive risk is about 30%. Thus, between 1992 and 2002
one out of every three cases is radiation-induced. Figure 2.13 presents a map with the values of cumulative
attributive risk of thyroid cancer in the population of the Oryol oblast. For the Dmitrovsky rayon the attributive risk
is as high as 50%, which means that of 5 out of 10 cases are radiation induced. The lowest attributive risk of
thyroid cancer of 16% occurs in the residents of the Dolzhansky rayon (the accumulated dose is 16 mGy).
Fig. 2.13. Map of the cumulative attributive risk of thyroid cancer for the child populations
of different rayons of the Oryol oblast as of 2002.
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"Radiation & Risk", 2003, special issue
2.5.2. Incidence of adults
As follows from the model, the radiation risk of thyroid cancer for adults exposed at the age older than 18
years this risk is half that in children. Since the accumulated doses in adults are lower than those in children (see
table 2.2), the attributive risk for this group will be much lower.
Figure 2.14 shows time trend in the number of background cases of thyroid cancer among the Oryol oblast
residents more than 14 years of age in 1986 (the size of this group was about 700 thousand people).
Fig. 2.14. Time trend in the number of background (spontaneous) cases of adult thyroid cancer among
the Oryol oblast residents more than 14 years of age in 1986.
In this age group, as can be seen from the figure, about 30 cases of background cancers are predicted (in
the current year 2002 this group includes people between the ages of 29-90). Due to aging the size of the group
is declining rapidly because of deaths (see Fig 2.7) and the number of cases is decreasing as well.
Figure 2.15 shows the time dependence of the cumulative (accumulated from 1992) number of thyroid
cancers in people who were older than 15 years in 1986. As follows from the figure, over the entire time of the
existence of this group the total number of thyroid cancers, by estimates, will be more than 1100 cases. The
lifetime number of radiation-induced cancers in this group is predicted to be about 8 cases. Accordingly, the
lifetime attributive risk is less than 1%.
The time dependence of attributive risk for the adult population of the Oryol oblast is shown in Fig. 2.16. As
can be seen from the figure, the attributive risk does not exceed 1.5 %. In the current year 2002 the attributive risk
is about 0.7% (of 100 cases less than one is radiation induced).
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"Radiation & Risk", 2003, special issue
Fig. 2.15. The same as in Fig. 2.14, but for cumulative number of cases starting
from 1992 (excluding the latent period of 5 years).
Fig. 2.16. The time trend of the attributive risk of thyroid cancer among
the Oryol oblast residents who were more than 14 years of age in 1986.
Figures 2.17 and 2.18 show the cumulative number of background and radiation-induced thyroid cancers in
the population of the Oryol oblast in 2002. In the Dmitrovky rayon where (the average accumulated dose is 22
mGy), according to the projection, there will be more than 7 background cases and 0.1 case of radiation-induced
thyroid cancers by 2002. In the most heavily populated Oryol rayon the number of background cases is 141 cases
and 1 case is radiation-induced.
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"Radiation & Risk", 2003, special issue
Fig. 2.17. Map of the cumulative number of background (spontaneous) thyroid cancer cases among adults
in the rayons of the Oryol oblast as of 2002.
Fig. 2.18. Map of the cumulative number of radiation-induced thyroid cancers among adults
in the rayons of the Oryol oblast as of 2002.
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"Radiation & Risk", 2003, special issue
Fig. 2.19. Map of the cumulative attributive risk of thyroid cancer for adult residents
of different rayons of the Oryol oblast as of 2002.
As of 2002 the cumulative attributive risk of thyroid cancer in those older 14 years in 1986 is low. On the
average, in the Oryol oblast the attributive risk is 0.8%. Thus, in the period from 1992 to 2002, of 100 cases less
than one is radiation-induced. Figure 2.19 presents a map with the values of cumulative attributive risk of thyroid
cancer in the populations of different rayons of the Oryol oblast. In the Dmitrovsky rayon the attributive risk is
1.7% - of 100 cases 2 are radiation induced. The lowest attributive risk of thyroid cancer of 0.4% is observed in
residents of the Dolzhansky rayon.
Conclusion
In this chapter, based on the model of radiation risks BEIR-V and software PUBASS the background and
radiation-induced incidence of thyroid cancer in children and adults of the Oryol oblast is predicted. The
prognostic estimates lead us to make the following conclusions.
The projection shows that between 1992 and 2002 the percentage of radiation-induced cases (cumulative
attributive risk) in children of the oblast, on average, will be 30% (each third case is radiation-induced). The
highest attributive risk of about 50% has been derived for the population of the Dmitrovsky rayon (accumulated
dose 84 mGy). During the indicated time period a total of 13 background cases of thyroid cancer is predicted to
have occurred among those under age 15 (children ) in 1986 and 6.4 cases are radiation induced.
For the adult population (age more than 14 years in 1986) of the Oryol oblast the attributive risk in 19922002 was estimated to be 0.8% or less than one in 100 cases. The highest attributive risk occurs in the
Dmitrovsky rayon - 1.7%.
References
1.
Health effects of exposure to low levels of ionizing radiation (BEIR V). - Washington, D.C.: National Academy Press, 1990.
2.
Trapeznikov N.N., Aksel E.M. Incidence of malignant neoplasms and deaths from them in the population of CIS countries
in 1996. - Moscow: ONTs RAMS, 1997. - 302 p.
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32