André Bouville NCI retired and Vladimir Drozdovitch NCI Workshop on Radiation and Thyroid Cancer Tokyo Japan 22 February 2014 1 Outline Background information Principles of dose reconstruction ID: 539967
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Slide1
Thyroid dose estimation for epidemiologic studies
André Bouville (NCI, retired) and Vladimir Drozdovitch (NCI)Workshop on Radiation and Thyroid CancerTokyo, Japan, 22 February 2014
1Slide2
Outline
Background informationPrinciples of dose reconstructionExamples of studies and dose estimatesConcluding remarks
2Slide3
Background information
3Slide4
Analytic epidemiologic studies
Requirement:Unbiased individual dose estimates for a large number of subjectsExamples of studies:Chernobyl: UA-US and BY-US studies among childrenChernobyl: UA-US in utero studyFallout: Marshall Islands study
4Slide5
Exposure PathwaysSlide6
Pasture-cow-milk pathway (131
I)Slide7
Principles of thyroid dose reconstruction in a large environmental study
7Slide8
Six Principles of Dose Reconstruction
8● Perform person-based measurements.● Administer interviews.
● Conduct environmental measurements.
● Obtain realistic estimates of dose.
●
Validate the dose estimates.
● Estimate the uncertainties attached to the dose estimates. Slide9
Principle #1: person-based measurements
9● Objective: perform as many person-based measurements as possible.●
Rationale
: dose estimates are much less uncertain when they are based on:
person-based measurements , than on
environmental radiation measurements, or on
data on activities released into the environment
.Slide10
Thyroid dose is propor-tional to area under the curve
0
5
10
15
20
25
30
0 20 40 60
20
40
60
Time after the accident(days)
I-131 activity
(
kBq
)
Measured
value.
Thyroid Dose Estimation (multiple measurements)
10Slide11
Thyroid dose is propor-tional to area under the curve
0
5
10
15
20
25
30
0
20
40
60
Time (days)
I-131 activity
(
kBq
)
Measured
value.
Curve derived from
131
I
models
plus data from
questionnaire
Thyroid Dose Estimation (usual case)
11Slide12
Principle #2: personal interviews
12● Objective: identify the conditions of radioiodine intake as early as possible.
●
Rationale
:
- the internal dose estimates are very sensitive to the conditions of radioiodine intake. It is important to clarify if inhalation occurred in a single day or over several days and if ingestion was a significant mode of exposure,
- because of memory loss, the personal interviews should be performed soon after the accident. Slide13
Personal interviewSlide14
Inhalation: r
esidence history (including number of hours spent indoors) during the first two months following the accidentIngestion: consumption rates and origin (market or own garden) of water, milk, and leafy vegetablesCountermeasures: sheltering, evacuation, and/or stable iodine administration, if conducted
14
Questions to interviewees
(in case of exposure to
131
I)Slide15
Principle #3: environmental measurements
15● Objective: development of a model predicting the variation with time of the intake rate of
131
I.
●
Rationale
:
- environmental measurements (
131
I in air
, water, soil, vegetation, foodstuffs +
137
Cs in air
and soil) are the best data that could supplement the person-based measurements,
- when environmental measurements are not available, estimates of released activities, combined with models of atmospheric transport, have to be used.
Slide16
137
Cs deposition map (Chernobyl accident)Slide17
Principle #4: realistic dose estimation
Principle #5: validation of dose estimatesPrinciple #6: estimation of uncertainties17
●
Objectives
:
obtain realistic (unbiased) estimates of dose for all
subjects
of the epidemiologic
study; make sure that the estimated doses are reasonably reliable; and quantify the uncertainties
●
Rationale
:
the dose
estimates
have to be credible and arguments must exist to defend their credibility. Slide18
Examples of studies and dose estimates
18Slide19
Chornobyl Accident – 26 April 1986
The most severe
accident that
ever occurred in
the nuclear
power industry.Slide20
NCI Chornobyl thyroid study
Cohort study of about 25,000 subjects (13,000 Ukrainians and 12,000 Belarusians) exposed as children.Lived in contaminated areas of Ukraine and Belarus.
All subjects had a person-based measurement (
131
I activity in the thyroid).
20Slide21
Distribution of thyroid dose estimates
21
Thyroid dose interval (
Gy
)
Number of subjects
Ukraine
Belarus
N
%
N
%
<0.2
6,729
51.0
5,407
46.1
0.2 – 0.49
2,829
21.4
2,867
24.4
0.5 – 1.99
2,735
20.7
2,812
24.0
2.0 – 9.99
838
6.3
612
5.2
≥10
73
0.6
34
0.3
All
13,204
100
11,732
100
Mean (Gy)
0.65
0.58Slide22
Distribution of GSD according to dose (Ukrainian cohort)
22
GSD interval
N
%
Mean thyroid dose (
Gy
)
≥3
217
1.6
0.017
2.0 – 2.99
294
2.2
0.26
1.5 – 1.99
4,711
35.7
0.68
1.26 – 1.49
7,982
60.5
0.66Slide23
In-utero study of thyroid cancer in UkraineNumber of subjects: 2,584, including three groups:
Subgroup L1-C
: 720 subjects. Their mothers:
lived in a
contaminated
area in April-June 1986; and
had a person-based measurement (
131
I activity in thyroid)
.
Subgroup L2-C
: 776 subjects. Their mothers:
lived in a
contaminated
area in April-June 1986; and
did not have a person-based measurement
, but
a number of women from the same settlement of residence had such a measurement.Subgroup L1-NC: 1088 subjects. Their mothers: lived in a non-contaminated area in April-June 1986; and did not have a person-bases measurement, and no other woman from the same settlement of residence had such a measurement.
23Slide24
Estimation of doses for the 2,584
in-utero subjects
24
Direct thyroid
measurements
(for 720 MOTHERS)
Subjects of
contaminated
areas
1496
Subjects of
“non-contaminated”
areas
1088
Individual Questionnaires
History
of pregnancy
Behavior:
milk consumption
leafy
vegetables
relocation
Sets of personal information
Slide25
25
Results
of
in utero
thyroid dose calculation
Thyroid dose,
mGy
Contaminated areas
(L1-C + L2-C)
“Non-contaminated” areas
(L1-NC)
Number of persons
%
Number of persons
%
0-20
577
38.6
934
85.8
20-50
281
18.8
124
11.5
50-100
219
14.6
23
2.1
100-200
186
12.4
7
0.6
200-500
158
10.6
-
-
500-1000
50
3.3
-
-
>1000
25
1.7
-
-
Total
1496
100
1088
100Slide26
1946-1958:
• 66
nuclear tests, ~100
MT
•
Release of
131
I:
150 Chernobyl
1500 Fukushima
• 1954: BRAVO test
Resulted in high doses in northern atolls and to evacuations.
Nuclear weapons testing in the Marshall IslandsSlide27
There are significant differences in estimating internal doses for Marshallese compared
to estimating doses to populations exposed to fallout from the Chernobyl or Fukushima accidents
:
No animal milk products
available.
2)
Unusual exposure pathways.Slide28
Bioassay of urine from
Rongelap
community members collected within 16 to19 days of fallout
exposure from the BRAVO test
provided the first ever measurements to confirm
131
I from exposure to fallout.
Marshall Islands: person-based measurementsSlide29
Estimates of thyroid dose (mGy
) to adults
Majuro
Kwajalein
Utrik
Rongelap
Internal dose
(short-term)
22
66
740
7,600
Internal dose (long-term)
0.76
1.3
25
14
INTERNAL DOSE (TOTAL)
23 67
760 7,600
EXTERNAL DOSE 9.8
22 140 1,60029Slide30
Concluding remarks
30Slide31
Concluding remarks (1 of 2)
All dose reconstructions are different because:Radioactive releases are differentEnvironmental conditions are differentPopulation habits are different, andCountermeasures are different.However, there are principles of dose reconstruction that apply to all environmental studies.
31Slide32
Concluding remarks (2 of 2)
It is important to obtain realistic estimates of dose because:they may be used in research projects such as epidemiologic studies or risk assessment, the affected populations have the right to know the extent to which they were exposed to radiation.
Multi-agency cooperation and multi-disciplinary expertise is needed to obtain dose estimates of a high degree of reliability.
32Slide33
33
Thank you for your attention