United Nations Scientific Committee on the Effects of Atomic Radiation

ATTACHMENT 1

POWER CALCULATIONS FOR EPIDEMIOLOGICALSTUDIES THAT UNDERPIN THE COMMENTARY ON
HEALTH IMPLICATIONS IN THE
2013 FUKUSHIMA REPORT
Developments since the 2013 UNSCEAR Report on the levels and effects ofradiation exposure due to the nuclear accident following the great east-Japan
earthquake and tsunami
A 2015 white paper to guide the Scientific Committee’s future programme of work

Notes
The designations employed and the presentation of material in this publication do not imply theexpression of any opinion whatsoever on the part of the Secretariat of the United Nations
concerning the legal status of any country, territory, city or area, or of its authorities, orconcerning the delimitation of its frontiers or boundaries.

©

United Nations, February 2016. All rights reserved, worldwide.

This publication has not been formally edited.

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Contents
I. GENERAL ASSUMPTIONS AND CALCULATION METHOD ....................................... 3
II. ALL SOLID CANCER .......................................................................................................... 4
A. Input.................................................................................................................................. 4
B. Assumptions ..................................................................................................................... 7
C. Results .............................................................................................................................. 7
III. THYROID CANCER ............................................................................................................. 8
A. Input.................................................................................................................................. 8
1. Exploratory analysis ................................................................................................... 8
2. Power calculations ...................................................................................................... 9
B. Assumptions ..................................................................................................................... 9
C. Results ............................................................................................................................ 10
1. Exploratory analysis ................................................................................................. 10
2. Power calculations .................................................................................................... 10
IV. LEUKAEMIA ...................................................................................................................... 11
A. Input................................................................................................................................ 11
B. Assumptions ................................................................................................................... 12
C. Results ............................................................................................................................ 13
V. BREAST CANCER ............................................................................................................. 13
A. Input................................................................................................................................ 13
B. Assumptions ................................................................................................................... 14
C. Results ............................................................................................................................ 15
ACKNOWLEDGEMENTS ....................................................................................................... 15
REFERENCES ........................................................................................................................... 15

1.
In this attachment, the Committee documents the data, assumptions, methodology andargument used to underpin its commentary on health implications for the public and workers
that was published in the 2013 report on levels and effects of radiation exposure due to the
nuclear accident after the 2011 great east-Japan earthquake and tsunami, the UNSCEAR 2013
Fukushima report (appendix E in [UNSCEAR, 2014]).

I.

GENERAL ASSUMPTIONS AND CALCULATION METHOD

2.
Assumption 1. The Committee assumed a linear dose response, and used estimates oflifetime attributable risks per unit dose, to estimate notional numbers of radiation-related casesin the most exposed population groups. District averages of doses estimated for the populationof Fukushima Prefecture were low. In the low dose region, radiation risks are uncertain. Thus
the “radiation-related cases” calculated here are nothing but notional and serve only to assess

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whether a radiation impact on health would likely be discernible or not. This assessment isvalid only under the condition of the assumptions made.
3.
Assumption 2. It was assumed, without further in-depth analysis, that a radiation effectwould not become discernible if the power from a statistical test to detect a difference between
a disease rate in the exposed subpopulation and the corresponding rate in the general
population (assuming a significance level of 0.05) is less than 80%. This statistical test wasapplied here assuming the following ideal conditions:− The baseline risk was known (rates of disease for Japan for the age/gender
subpopulation);− Health effects in the subpopulation could be detected without any loss in follow-up;− Cancer registries were complete.
The study design was a cross section (screening study); incidence could be estimated for thetime period between the first and the last screening.
4.
The number of cancer cases in each group could be considered as a Poisson-distributed
number or the sum of binomial-distributed values. The test statistic could be considered basedon the exact test for two Poisson-distributed values (see [Breslow and Day, 1987]), the ChiSquared test using approximation of normal distributions (see e.g. [UNSCEAR, 2000, Vol. II]).
For the purpose of this attachment, the t-test was used as an approximation to compare
proportions in two independent groups [Program G*Power]. Using either exact Poisson
distributions or an approximation with binomial distributions give similar results for the area ofinterest, say statistical power in the order of 50–90%. Calculations were compared with the“exact Fisher Test”, the exact Poisson test for group data and with the normal distribution
approximation. For very small P and medium sample size, the different methods andapproximation methods yielded slightly different results, but this was less relevant compared to theother uncertainties and did not influence the conclusions about discernibility.

II.

ALL SOLID CANCER

5.
The Committee addressed whether an increased incidence of all solid cancers combined
was expected to be discernible in paragraph E28 of [UNSCEAR, 2014].
A.

Input

6.
Tables 1 and 2 present relevant information derived from the Committee’s estimates ofeffective doses to people (both evacuated and not evacuated) from Fukushima Prefecture(attachment C-14 of [UNSCEAR, 2014]). Table 1 presents estimates for the numbers of peoplein Fukushima Prefecture who received doses in the uppermost interval for the average effective
dose in the first year after the accident. For those not evacuated, the estimates considered were
those for people in districts of Fukushima Prefecture with doses in the uppermost dose interval.
For those evacuated, the estimates were for those people who followed evacuation scenariosthat led to doses in the uppermost interval. Table 2 shows the upper values of average effective
dose in the first year and cumulative effective dose to 80 years of age in districts of Fukushima
Prefecture that were not evacuated. Table 3 presents estimated lifetime baseline and notionalradiation-associated risk of all solid cancers (excluding thyroid cancers due to the excess
thyroid dose over colon dose) for population groups in the regions with the highest deposition,
taken from [WHO, 2013].

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Table 1. Assumed numbers of non-evacuated persons in districts of Fukushima Prefecture in
the uppermost interval of the average first-year effective dose and of evacuated persons
following evacuation scenarios with doses in the uppermost interval of average first-year
effective dose (based on attachment C-14 to [UNSCEAR, 2014])
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Interval of effective dose (mSv)

Assumed population with doses
in dose interval

Non-evacuated adults

4 to 5

252 642

Non-evacuated children

5 to 636 715Non-evacuated infants

7 to 814 513

Evacuated adults

9 to 10

1 109

Population group

Table 2. Upper values of average first-year and cumulative (up to age 80 years) effective dose topeople in non-evacuated districts of Fukushima Prefecture (table C14 in [UNSCEAR, 2014])
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Population groupFirst-year effective dose (mSv)

80-years effective dose (mSv)

Non-evacuated adults

4.3

11

Non-evacuated children

5.9

16

Non-evacuated infants

7.5

18

Table 3. Estimated lifetime baseline and radiation-associated risk of all solid cancer (excluding
thyroid cancers due to excess of thyroid dose over colon dose) for population groups living for
four months in the regions with the highest deposition density and subsequently in the western
least contaminated region of Fukushima Prefecture (tables 34, 35 and 36 in [WHO, 2013])
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Population group
Women

Lifetime colon dose (mGy)

Baseline risk

Radiation-associatedrisk estimate

23

29.07 × 10−20.59 × 10−2−20.39 × 10−2

Men

23

40.74 × 10

Girls

26

29.09 × 10−20.86 × 10−2−20.57 × 10−2

Boys

26

40.71 × 10

Female infants

27

29.04 × 10−2

1.11 × 10−2

Male infants

27

40.60 × 10−20.73 × 10−2

7.
Cancer registries in Miyagi, Yamagata, Fukui and Nagasaki prefectures wereconsidered to be relatively complete since 1985 [Katanoda et al., 2012]. The age standardized
annual cancer incidence in 2000 to 2004 in Miyagi and Nagasaki was about 450 cases per
100,000 males, and in Fukui and Yamagata about 380 cases per 100,000 males (figure I).
Correspondingly, the annual incidence was about 270 cases per 100,000 females in Miyagi andNagasaki prefectures, and about 230 cases per 100,000 females in Fukui prefecture.

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Figure I. Age standardized annual cancer incidence in five prefectures of Japan [Katanoda et al., 2012]

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B.

7

Assumptions

8.
Assumption 3. The 80-year cumulative effective dose to people in the district with thehighest average dose, E80 (table 2), may be applied to the population, Pupper, in the uppermost
dose interval of the dose distribution calculated in attachment C-14 to [UNSCEAR, 2014].
Calculations were performed for females and males separately. In both cases Pupper was
assumed to be 50% of the value for the total population in table 1.
9.
Assumption 4. Notional numbers of lifetime radiation-associated cases of all solidcancer (excluding thyroid cancers due to excess of thyroid dose over colon dose) may be
estimated by a linear dose response with a radiation-associated risk per unit dose, Rsc (derived
from table 3):
Nsc,attr = Pupper E80 Rsc
10.
Assumption 5. An upper estimate of the lifetime dose of the evacuees for the scenario
with the highest first-year dose may be obtained by adding the difference of the lifetime dose
and the first-year dose in the district with the highest first-year dose. According to tables 1 and 2,
the upper estimate for the lifetime effective dose of adult evacuees would be 16 mSv.
11.
Assumption 6. The upper estimate of the lifetime dose of adult evacuees for the scenario
with the highest first-year dose may be combined with the radiation-associated risk per unit
dose for non-evacuated persons to obtain an estimate of the number of notional radiationassociated cases.
C.

Results

Table 4. Estimated numbers of baseline and notional radiation-associated cases of solid cancer inthe most exposed populations groups as defined in table 1, excess relative risks, and power todetect the increased risk comparing the estimate to the baseline risk for Japan (one-sided test)
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities. Note that calculations are based on radiation-associated risks
per unit dose for the scenario of relocated people (table 3), which are slightly higher than those for non-evacuatedpeople and slightly lower than those for evacuated people
Population group

Nsc,base

Nsc,attr

ERR

Power

Non-evacuated women

36 722

351

0.010

73%

Non-evacuated men

51 463

232

0.005

43%

Non-evacuated girls

5 340

96

0.018

53%

Non-evacuated boys

7 473

64

0.009

–*

Non-evacuated female infants

2 107

54

0.025

<50%

Non-evacuated male infants

2 946

35

0.012

–*

Evacuated women

161

2.2

0.014

–*

Evacuated men

226

1.6

0.007

–*

* <30%.

12.
If non-evacuated women and men were to be studied together, then the power would
amount to 82%. The power would be even greater, if all eight population groups would bestudied together. However, considering the large differences of cancer incidence rates in the
different prefectures of Japan (figure I) an excess relative risk of 1% is not expected to bediscernible, if a control group with the same baseline incidence as in the exposed group is notdefined. Moreover, defining a control group of similar size, with similar age and sex structure

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and with the same baseline risk seems almost impossible taking into account the large variation
in incidence rates in Japan. Breaking down the population of Fukushima Prefecture into
exposed and non-exposed subpopulations would already reduce the power to less than 80%.

III. THYROID CANCER
13.
The Committee addressed whether an increased incidence of thyroid cancers was
expected to be discernible in paragraph E32 of [UNSCEAR, 2014]. Individuals in a
subpopulation of Fukushima Prefecture were being screened for thyroid diseases. Therefore, itwould not be appropriate to base power calculations for thyroid cancer on national rates forJapan, but rather on the expected thyroid cancer incidence in the screened population.
A.

Input

1.

Exploratory analysis

14.
Table 5 presents estimates of the baseline and radiation-associated risk of thyroid
cancer among persons having been exposed as infants while living for four months in theregions with the highest deposition density and then subsequently in the western leastcontaminated region of Fukushima Prefecture, as presented in table 37 of [WHO, 2013].
Table 6 gives an estimate of baseline and radiation-associated risk of thyroid cancer after
exposure during infancy to a dose to the thyroid of 100 mGy under the conditions of intensive
screening as currently performed in Fukushima Prefecture [Jacob et al., 2014].
Table 5. Baseline and estimated radiation-associated risk of thyroid cancer among persons
exposed as infants while living for four months in the regions with the highest deposition
density and subsequently in the western least-contaminated region of Fukushima Prefecture,neglecting the effect of screening (table 37 in [WHO, 2013])
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Lifetime thyroid dose (mGy)

Baseline risk
without screening

Radiation-associatedrisk estimate

Female1220.77 × 10−20.52 × 10−2

Male

122

0.21 × 10−20.12 × 10−2

Sex

Table 6. Baseline and estimated radiation-associated risk of thyroid cancer risk among persons
exposed as infants with a thyroid dose of 100 mGy considering the effect of screening [Jacob etal., 2014]
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Period after exposure (years)

Baseline risk
with screening

Radiation-associatedrisk estimatea

Female200.089 × 10−20.12 (0.007; 0.51) × 10−2

Female50

2.3 × 10−2

1.4 (0.11; 4.6) × 10−2

Sex

Male
a

Best estimate and 95% confidence interval.

50

0.52 × 10−20.30 (0.015; 1.2) × 10−2

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2.

9Power calculations

Table 7. Estimated baseline and average radiation-associated increased risk of thyroid cancer
among the population screened in Fukushima Prefecture, considering the estimated influence ofscreening for two time periods after exposure [Jacob et al., 2014]
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Thyroid dose (mGy)

Period after exposure (years)

Baseline risk
with screening

Radiation-associatedrisk estimatea

20

20

0.23 × 10−2

0.021 (0.0007; 0.081) × 10−2

20
a

50

2.2 × 10−20.13 (0.005; 0.40) × 10−2Best estimate and 95% confidence interval.

Table 8. Infants in areas of Fukushima Prefecture with first-year thyroid doses from external
exposure and inhalation that exceeded 10 mGy or were less than 3 mGy (attachment C-16 of[UNSCEAR, 2014])
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantitiesa

Thyroid dose (mGy)

Whole population

Screeneda

Girls <3 yearsa>10740 000

111 000

11 000<3

444 000

66 0006 600

Based on assumption 9.

B.

Assumptions

15.
Assumption 7. Lifetime radiation-associated risk of thyroid cancer may be estimated bya linear dose response with a risk per unit dose, Rth (derived from tables 5, 6 and 7).
16.

Assumption 8:− The (simple) null hypothesis, H0, that there is no increased risk for exposed persons(that is Pexp = Pnonexp);− The alternative hypothesis, H1, that there is an increased risk for exposed persons (thatis Pexp > Pnonexp, which is a one-sided test);− Accepted error Type 1 (i.e. probability that H0 is correct and the study concludes it tobe wrong) of 5%;− t-test to compare proportions in two independent groups, using the approximation of
binomial distribution;− Study design: cross-section (screening) study, where the incidence can be estimated forthe time period between the first and the last screening;− Software: program G Power [Program G*Power].

17.
Assumption 9. In a hypothetical epidemiological study, thyroid cancer incidence would
be compared between population groups living in districts of Fukushima Prefecture who
received first-year thyroid doses as infants from external exposure and inhalation that exceeded
10 mGy or were less than 3 mGy. Based on population statistics in Japan, it was assumed thatthe screened population constituted 15% of the total population, and that girls younger than
3 years constituted 1.5% of the total population. It was further assumed that the difference

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between the average lifetime thyroid dose for the two groups of districts amounted to 10 mGy
for the whole of the screened population, and to 20 mGy for females exposed as girls younger
than 3 years.
18.
Assumption 10. The value of the risk per unit dose could be higher than the best
estimate used in the power calculations. Thus, additional power calculations were performed
assuming values of risks from radiation exposure that were 2.5 times higher than the best
estimate. In further calculations it was assumed that the size of the control group was twice thatof the main analysis.
C.

Results

1.

Exploratory analysis

19.
Based on calculations in [WHO, 2013], the lifetime relative risk for female infants with thethyroid dose of 50 mGy amounted to (0.52 × 50/122 + 0.77) / 0.77 = 1.28. For male infants with thethyroid dose of 50 mGy, the lifetime relative risk amounts to (0.12 × 50/122 + 0.21) / 0.21 = 1.23.
20.
Based on calculations of Jacob et al. [Jacob et al., 2014], the relative risk 50 years after
exposure for female infants who received a thyroid dose of 50 mGy amounts to(1.4 × 50/100 + 2.3) / 2.3 = 1.30. For male infants who received a thyroid dose of 50 mGy, therelative risk amounts to (0.3 × 50/100 + 0.52) / 0.52 = 1.29.
2.

Power calculations

Table 9. Power of theoretical epidemiological studies of thyroid cancer incidence in Fukushima
Prefecture for two time periods after the accident
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Population

Dhigh – Dlow (mGy)

All screened

10

Girls <3 years
Girls <3 years
Non-exposed
doubled20
20

Radiation-associated risk

20 years after
exposure

50 years after
exposure

Best estimate

11%

–*

2.5 × best estimate

28%

70%

Best estimate

11%

31%

2.5 × best estimate

27%

87%

Best estimate

14%

40%

* <30%.

21.
On purely statistical grounds, and conditional on the above assumptions being valid, anincreased incidence of thyroid cancer due to radiation exposure might theoretically bediscernible, if:− The health of females exposed before the age of 3 years would be followed for the next
50 years;− Their average thyroid dose were larger than the one in a control group by at least
20 mGy;ATTACHMENT 1: POWER CALCULATIONS FOR EPIDEMIOLOGICAL STUDIES [...]

11− The risk for radiation-induced thyroid cancer were actually a factor of 2.5 higher thanthe best estimate in Jacob et al. [Jacob et al., 2014];− All persons could be followed-up for decades.

IV. LEUKAEMIA
22.
The Committee addressed whether an increased incidence of leukaemia was expected
to be discernible in paragraphs E34 and E35 of [UNSCEAR, 2014].
A.

Input

Table 10. Number of non-evacuated persons in districts of Fukushima Prefecture and of evacuatedpersons for evacuation scenarios who received an average dose to red bone marrow dose greaterthan 4 mGy in the first year (see assumptions 11 and 12)
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Population group

Range of red bone marrow dose (mGy)Size of population with doses in range

Non-evacuated adults

4 to 5

252 642

Non-evacuated children

4 to 677 863Non-evacuated infants

4 to 862 522

Evacuated adults

4 to 1044 016

Table 11. Average doses to red bone marrow in the first-year and accumulated up to age 80 years ofpeople in non-evacuated districts of Fukushima Prefecture — and of evacuees for evacuation
scenarios — who received doses greater than 4 mGy in the first year (see assumptions 12, 13 and 15)
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Red bone marrow dose in the first year
(mGy)

Red bone marrow dose accumulated toage 80 years (mGy)

Non-evacuated adults

4.3

11

Non-evacuated children

5.0

14

Non-evacuated infants

5.6

13

Evacuated adults

6.3

13

Population group

Table 12. Lifetime baseline and estimates of radiation-associated risk of leukaemia for populationgroups in regions with highest deposition densities (tables 34, 35 and 36 in [WHO, 2013])
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Population group
Women

Lifetime red bone marrow dose (mGy)

Baseline risk

Radiation-associatedrisk estimate

22

0.40 × 10−20.009 × 10−2−20.015 × 10−2

Men

22

0.57 × 10

Girls

26

0.41 × 10−20.014 × 10−2

Boys

26

0.58 × 10−20.020 × 10−2−20.027 × 10−20.040 × 10−2

Female infants

26

0.43 × 10

Male infants

26

0.60 × 10−2

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Table 13. Cumulative baseline and estimated radiation-associated risk of childhood leukaemia inregions with highest deposition densities (table 40 in [WHO, 2013])
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Population group15-years red bone marrow dose (mGy)

Baseline risk

Radiation-associatedrisk estimate

26

0.03 × 10−20.017 × 10−2−20.025 × 10−2

Female infants
Male infants

B.

26

0.03 × 10

Assumptions

23.
Assumption 11. Leukaemia is a relatively rare disease. The number of leukaemia cases
among non-evacuated children and infants, and among evacuated adults in the uppermost doseintervals will be small. Thus, larger population groups of size P>4mGy, defined by red bonemarrow doses exceeding 4 mGy, are considered here.
24.
Assumption 12. Numerical values of effective dose (in millisieverts) may be used toapproximate the absorbed dose to red bone marrow (in milligrays). Calculations are performed
for females and males separately. In both cases P>4mGy is assumed to be 50% of the value forthe total population in table 10.
25.
Assumption 13. Lifetime red bone marrow doses may be estimated from first-year redbone marrow doses by multiplication with the ratio of lifetime effective doses and first-year
effective doses as derived from table 2.
26.
Assumption 14. Notional numbers of radiation-associated cases of leukaemia during
lifetime and of childhood leukaemia may be estimated by a linear dose response with aradiation-associated risk per unit dose, Rlk (derived from tables 12 and 13):For lifetime:Nlk,attr = P>4mGy D80 Rlk

For childhood: Nlk,attr = P>4mGy D15 Rlk
27.
Assumption 15. An upper estimate of the lifetime dose to evacuees for the scenario withthe highest first-year dose may be obtained by adding the difference of the lifetime dose andthe first-year dose in the district to the highest first-year dose.

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C.

13

Results

Table 14. Estimated numbers of baseline and notional radiation-associated cases of leukaemia
during lifetime of the most exposed population groups as defined in table 10
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities. Note that calculations are based on radiation-associated risks
per unit dose for the scenario of relocated people (table 13), which are slightly higher than those for non-evacuatedpeople and slightly lower than those for evacuated people
Population groupNlk,base

Nlk,attr

ERR

Power

Non-evacuated women

505

5.6

0.011

–*

Non-evacuated men

720

9.3

0.013

–*

Non-evacuated girls

160

2.9

0.018

–*

Non-evacuated boys

226

4.1

0.018

–*

Non-evacuated female infants

134

4.2

0.031

–*

Non-evacuated male infants

188

6.2

0.033

–*

Evacuated women

88

1.1

0.013

–*

Evacuated men

125

1.9

0.015

–*

* <30%.

Table 15. Estimated numbers of baseline and notional radiation-associated cases of childhood
leukaemia in the most exposed populations groups as defined in table 10
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Population groupNlk,base

Nlk,attr

ERR

Power

Non-evacuated female infants

9.4

2.7

0.28

–*

Non-evacuated male infants

9.4

3.9

0.42

–*

* <30%.

V. BREAST CANCER
28.
The Committee addressed whether an increased incidence of breast cancer was
expected to be discernible in paragraph E36 of [UNSCEAR, 2014].
A.

Input

Table 16. Number of non-evacuated females in districts of Fukushima Prefecture — and of evacuatedfemales — with average breast dose greater than 4 mGy in the first year(see assumptions 16 and 17)
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Population group

Range of breast dose (mGy)

Population in range

Non-evacuated adults

4 to 5

126 321Non-evacuated children

4 to 638 932Non-evacuated infants

4 to 831 261

Evacuated adults

4 to 1022 008

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Table 17. Average first-year and cumulative breast dose up to age 80 years in non-evacuateddistricts of Fukushima Prefecture and in evacuation scenarios exceeding first-year doses of
4 mGy (see assumptions 17, 18 and 20)
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Breast dosein the first year (mGy)Breast dose
accumulated to age 80 (mGy)

Non-evacuated adults

4.3

11

Non-evacuated children

5.0

14

Non-evacuated infants

5.6

13

Evacuated adults

6.3

13

Population group

Table 18. Lifetime baseline and radiation-associated risk of breast cancer for females in regionswith highest deposition densities (tables 34, 35 and 36 in [WHO, 2013])
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities
Population group exposed as

Lifetime breast dose (mGy)

Baseline risk

Radiation-associated risk

−20.13 × 10−2

Adult

24

5.6 × 10Girl

26

5.5 × 10−20.22 × 10−2−20.36 × 10−2

Infant28

B.

5.5 × 10

Assumptions

29.
Assumption 16. Considering the small relative risk implied by table 18, the total numberof notional radiation-related cases will be the deciding quantity in the power calculations.
Thus, as for leukaemia, not only persons in the group with the uppermost levels of dose, butlarger populations groups of size P>4mGy (defined by first-year doses to the breast exceeding
4 mGy) are considered here.
30.
Assumption 17. Numerical values of effective dose (in millisieverts) may reasonably
also be used to approximate the absorbed dose to the breast (in milligrays).
31.
Assumption 18. Lifetime dose to the breast may be estimated from the first-year dose to
the breast by multiplication with the ratio of lifetime effective doses and first-year effective
doses as derived from table 2.
32.
Assumption 19. Numbers of notional radiation-associated cases of breast cancer may be
estimated using a linear dose response with a risk per unit dose, Rbc (derived from table 18):
Nbc,attr = P>4mGy D80 Rbc
33.
Assumption 20. An upper estimate of the lifetime dose to the evacuees who followed
the scenario leading to the highest first-year dose may be obtained by adding the difference ofthe lifetime dose and the first-year dose in the district to the highest first-year dose.

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C.

15

Results

Table 19. Estimated numbers of baseline and notional radiation-associated cases of breast
cancer during the lifetime of the most exposed population groups as defined in table 16
The number of significant figures presented in the table are for purposes of calculation only; they do not imply sucha degree of accuracy in the underlying quantities. Note that calculations are based on radiation-associated risks
per unit dose for the scenario of relocated people (table 18), which are slightly higher than those for non-evacuatedpeople and slightly lower than those for evacuated people
Population groupNbc,base

Nbc,attr

ERR

Power

Non-evacuated women

7 011

74

0.011

–*

Non-evacuated girls

2 157

47

0.022

–*

Non-evacuated female infants

1 729

52

0.030

35%

Evacuated women

1 221

15

0.012

–*

* <30%.

ACKNOWLEDGEMENTS
The Committee would like to express its appreciation to P. Jacob (Germany), who led the
preparation of material for this attachment, and to M. Blettner (Germany) for statistical advice
and calculations of statistical power.

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