considerations for nas pilot studynas-sites.org/cancerriskstudy/files/2014/02/epri.pdf · antone...

Antone BrooksHelen Grogan

David HoelErik HoelArt Rood

Phung TranRichard Wakeford

Bill Wendland

NAS Public MeetingApril 3, 2014

Considerations for NAS Pilot Study

2© 2014 Electric Power Research Institute, Inc. All rights reserved.

EPRI Team

Presenters:• Phung Tran, MHS- Electric Power Research Institute• Richard Wakeford, PhD – University of Manchester• David Hoel, PhD – Medical University of South Carolina• Art Rood, MS- K-Spar, Inc.

Additional team members in attendance and available to answer questions:

• Tony Brooks, PhD- Washington State University Tri-cities (retired)

• Helen Grogan, PhD – Cascade Scientific• Erik Hoel, PhD- ESRI• Bill Wendland, PE- CN Associates


Contents

• EPRI, EPRI Study Scope, and Approach• Differences in Study Designs and Expectations

– Ecological and record based case control• Evaluation of Data Needs

– Census– Cancer Registries– Releases, Exposure, and Dose Assessments

• Interpretation of Study Results– Addressing Confounders– Statistical Power– Examples

EPRI, EPRI Study Scope and Approach


Electric Power Research Institute (EPRI) Our Mission…

To conduct research onkey issues facing the

electricity sector…on behalf of its members, energy

stakeholders, and society.


Three Key Aspects of EPRI

NonprofitChartered to serve the public benefit

IndependentObjective, scientifically based results address reliability, efficiency, affordability, health, safety and the environment

CollaborativeBring together scientists, engineers, academic researchers, industry experts

Founded in 1972 by Dr. Chauncey Starr


Data Quality Analysis and Recommendations to National Academy for Pilot Sites• 2013-2014:Develop more specific

recommendations for study design based on assessment of pilot site data:

plant related vsbackground radiation,

population sizes and characteristics

quality of cancer mortality and incidence data,

assessment of other sources and types of potential exposure

Brief NAS committee and/or NRC as necessary

Ensure More Meaningful Study

Results

Formal Comments on NAS Reports

Risk Interpretations

Study Design Considerations

Study Designs and Expectations


Phase I Report

“Statistical power calculations based on estimated exposure estimates indicate that extremely large sample sizes are required except under the following scenarios:A. Routine releases from the operating facilities have been far greater than those reported to the USNRC, orB. Sensitivity to radiation as characterized in most or all generally accepted risk models is either inappropriately low or simply irrelevant to the populations living near nuclear facilities in the United States.”(Section 4.2.1, Page 153)


Epidemiologic Study Designs

• “Ecologic” study– Relates group-averaged disease rates to group-averaged

exposures – basically an exploratory study design– As a geographic correlation study, an ecologic study

requires: number of health events in a given area, population in the area, average “exposure” in the area

– At a minimum, must have available: reliable mortality/registration data for the area, reliable population data for the area, some reliable measures of “exposure” for the area

– Challenges: accuracy of mortality/registration data, accuracy of population data, “snapshot” health event data, “snapshot” population data, migration of cases and population, “ecologic fallacy”, confounding factors


Epidemiologic Study Designs

• Record-linkage-based Case-control study– Individual-based: compares the frequency of occurrence of

factors among cases to that among controls, using available records (rather than interview data)

– Requires reliable mortality/registration data to identify cases, a reliable database (e.g. a population registry) from which to select controls, reliable measures of “exposure” (including historical), reliable measures of confounding factors

– Challenges: selection/information biases, inaccurate/incomplete mortality/registration data, lack of adequate databases from which to select representativecontrols, lack of adequate “exposure” measures, migration, lack of data to adjust for confounding, unknown major confounding factors

Evaluation of Data Needs


Summary Comments on Census Data and Cancer Registries• Significant challenges are presented because of the focus on small

areas around nuclear facilities, as highlighted by some European studies

• CENSUS– Both census tract and zip-code areas can be very large and extend

well beyond the NPP.– The available census data at the block level began in 1990.– Significant population changes have occurred since the 1990’s.

• CANCER REGISTRIES– Many of the cancer registries began in mid to late 1980’s. This limits

the analyses to the more recent years with lower exposures.– Cancer registry information may have incorrect current address for

some individuals.– Address at birth for cases may not be available for case control study


Geographic Area by Zip Code

• Zip codes represent large areas

• Urban vs rural• 3 nuclear power

plants within 50 km• Non-uniform

population distribution within zip code

• Joliet population doubled in 20 yrs.


Population Ratio (-) Distance (km)Zip Code

Town 1990 2000 2010 2010/1990

To Dresden

To Braidwood

60410 Channahon 3870 7585 12687 3.3 8.4 21.760416 Coal City/

Diamond6248 7288 9397 1.5 11.3 7.2

60450 Morris 13423 19114 20332 1.5 13.1 20.960447 Minooka 6005 7295 13709 2.3 14.2 30.660408 Braidwood 3814 5077 5696 1.5 14.6 2.560421 Elwood 2700 3516 3968 1.5 15.8 23.460407 Godley/

Braceville1535 1604 1684 1.1 16.6 2.6

60481 Wilmington/Custer

11034 11346 11851 1.1 16.8 10.5

60444 Mazon 3909 1545 1761 0.5 19.8 15.4

Population Reported by Zip Code in Three Consecutive Censuses (1990, 2000, 2010)


Detailed Census Block Data in ArcGIS Format for Population < 18 Years within 3- and 5- km Radius of Dresden NPP

• Population within 5 km (534 census blocks) , age < 5 years = 1,133• Expect about 1 leukemia case every 11 years among those age<5 years

(very low background leukemia)

• Based on 2010 Census

• Orange lines = Census Tracts

• Census Tracts may not give better resolution than zip code

• Purple = Population Numbers by Block (binned according to key)

• Key Points:

– Small populations

– Small number of cases

– Extremely low power


Mailing address used instead of actual residential address

Boice et al. 2009 - Pennsylvania cancer registry

Potential Study Bias: Cancer Registry may have Incorrect Residential Location


Phase I Report



Overview of Dose Assessment Methodology

uvcpDETSDose )( where

S = source term

T = environmental transport

E = exposure factors

D = conversion to absorbed dose

u = uncertainty analysis

v = validation

c = communication of results

p = participation of stakeholders.

Source: Till and Grogan (2008). Radiological Risk Assessment and Environmental Analysis. Oxford University Press, New York.


Source Term Issues• Significant effort will be needed to quantify source term• Assessment of radiation doses requires radionuclide-specific

release rates– 14C and 3H are in the ARERRsa, but other radionuclides would

have to be estimated or extracted from examination of NPPs records

– Not all radionuclide releases are important in terms of dose (e.g. short-lived noble gases)

– Doses from liquid releases may be addressed through environmental monitoring data

• Short term releases not readily available/easily accessible

aCarbon-14 atmospheric releases available from 2010 and could be estimated for prior years using acknowledged methodologies.


Atmospheric Transport Modeling

• Large study domain and complex terrain environments for some NPPs require non steady-state models capable of simulating spatially variable wind fields.

• 5 years of quality meteorological data is recommended instead of using historical records, which are unlikely to be available.

• Episodic releases can by assessed using a distribution of short-term dispersion factors that reflect the time of release

CALPUFF simulation of plume emitting from the Hanford reservation exhibiting effects of spatially variable wind field on plume dispersion

UTM

Nor

th (m

)

• Distance is a poor surrogate for dose

• Wind fields are spatially variable


Dose Assessment Methodology

• Modular approach to the all-pathways dose assessment model

– Allows substitution of site-specific transport and transfer models

• Use measured data when quantity and quality of measurements are available


Carbon-14 (Source: UNSCEAR 2000 Report)

14C 50% ingestion*

* Based on 2010 Dresden Releases


Why Worry about Validation?• To address the

potential criticism that releases from the operating facilities have been far greater than those reported to the USNRC

• Because we rely on computer models for dose calculations

Opportunities for Validation• Tree ring sampling coupled with modern detection techniques • Soil and sediment profile measurements for relatively immobile

particulate radionuclide releases


Summary of Recommendations for Dose Assessment

uvcpDETSDose )(

For epidemiological dose assessments:

Derive radionuclide specific source terms from original site data

Use site specific transport models

Review land use census to evaluate behavior patterns of individuals and populations

Evaluate/perform field measurements to confirm historical and current release estimates and models

Interpretation of Study Results


Phase I Report



Interpretation of Study Results

• Studies have been plagued by problems of design, conduct and interpretation, although there is some evidence (not yet persuasive) of a raised risk of leukemia in young children (<5 years of age) living close (<5 km) to (some) nuclear facilities.

• The elimination of selection/information biases has proved to be very difficult.

• Unidentified major confounding factors remain a major deficiency in interpretation – are people/areas around nuclear facilities different in terms of their background risks?

– evidence from potential nuclear sites

– patterns of infection (potentially important for childhood leukemia) may be different around nuclear facilities.

• Examples of statistical power and interpretation.


Variation in Excess Relative Risk of Leukemia with Age at Exposure (AAE) and Time Since Exposure (TSE)


Childhood Leukemia and Background Radiation

• Current radiation-induced leukemia risk models (e.g. BEIR VII) suggest that ~15-20% of childhood leukemia cases in Great Britain are attributable to natural background radiation (giving an average RBM dose of 1.4 mSv per year)

• Statistical power calculations indicate that a case-control study with at least 8000 cases would be required to have a power of ≥80% to detect the predicted influence of natural background radiation in Great Britain – mainly from gamma-rays rather than radon.

• The National Registry of Childhood Tumours (NRCT) has provided data for a case-control study of ~27 500 childhood cancer cases (~9000 leukemia cases) and ~37 000 matched controls in Great Britain during 1980-2006.


County Districts of Great Britain

• Average natural background gamma-ray dose-rates in 459 county districts (based on 2283 indoor measurements) were applied to maternal residences at birth of cases and matched controls.

• Indoor radon concentrations based on a predictive map generated from ~400,000 domestic radon measurements.

• Adjustments made for socio-economic status (based both on paternal occupation and county district deprivation index).

Great Britain = England,

Scotland and Wales


Dose-response Relationships

• A statistically significant dose-response, with an ERR at 10 mSv of 1.2 (95% CI: 0.3, 2.2), was found for gamma radiation and leukemia, but not for other cancers.

• No significant results for radon.

• Findings compatible with predictions of current leukaemia risk models.

• Second phase of study now underway.

• Initial results indicate that leukaemia risk model may apply to low doses/dose-rates, but no indication of gross underestimation of risk.


Low Dose Risk

• The radiosensitivity of childhood leukemia is particularly high.• The natural background radiation study suggests that low

doses/dose-rates might increase the risk.• It has taken a very large case-control study covering the

whole of Great Britain over 27 years to be capable of (possibly) detecting this small increased risk.

• The findings are compatible with the predictions of standard risk models, and do not indicate a wild underestimation of risk.

• The RBM dose from natural gamma-rays is ~1 mGy per year.• How large would a study have to be to detect the effect of an

RBM dose of ~1 μGy per year?


Internal Emitters

• Perhaps the risk of leukemia from the intake of, and internal exposure to, anthropogenic radionuclides (plutonium, strontium, etc.) has been seriously underestimated.

• Atmospheric nuclear weapons testing injected substantial quantities of these radionuclides into the environment.

• A marked “spike” of doses from weapons testingradionuclides occurred in the late-1950s and early-1960s (before signing of Limited Test Ban Treaty).

• Has this dose “spike” had a detectable influence upon childhood leukemia incidence rates around the world, a signal of a radical underestimation of leukemogenic risk from anthropogenic radionuclides?


Average Annual Effective Doses from Ingestion and Inhalation of Radionuclides Produced in Atmospheric

Nuclear Weapons Testing

Source: UNSCEAR 2000 Report


Incidence Rate of All Leukemiasa Among Young Children Aged 0-4 Years

• If anthropogenic radionuclides are much more potent than currently understood, an upwards step in risk should be apparent during the early- to mid-1960s.

• No marked increase in risk is apparent.

• Southern Hemisphere rates are similar to Northern Hemisphere rates, despite the difference in radioactive fallout levels.a Except where indicated otherwise (AL = acute leukemia; ALL = acute lymphoblastic leukemia).

Error bars show 95% Confidence Intervals for rates.


Background Risk of Cancer

• Nationwide studies of childhood cancer incidence in Great Britain have shown spatial variations beyond what might be expected from random variations.

• This suggests that major risk factors are distributed in a geographically non-uniform manner.

• Spatial non-uniformity of risk graphically illustrated by the extreme childhood leukemia “cluster” at Fallon (Nevada).

• This background presents great difficulties to a reliable interpretation of reported excesses of childhood leukemia near some nuclear installations.

Together…Shaping the Future of Electricity

Back-up Slides for Dose Assessment


Examples of Other Validation Techniques

• 14C measurements in tree rings match fallout and identified previously unknown releases

• Concentration of 3H in tree rings match temporal trend of releases from site

14C and 3H Measured in Tree Rings Near Lawrence Berkeley (Love et. al. 2003)


Example of Uranium Deposition in Soil

(Adapted from Rood et al. 2005)

Back-up Slides for Interpretation of Study Results


Tritium (Source: UNSCEAR 2000 Report)


Incidence Rate of All Leukemiasa Among Children Aged 0-14 Years

a Except where indicated otherwise (AL = acute leukemia; ALL = acute lymphoblastic leukemia)

Error bars show 95% Confidence Intervals for rates.


Other Exposures (EPA Toxic Release Inventory Program)

• Sources of non-nuclear, chemical carcinogen releases

Back-up Slides for Health Effects


Tritium: Biological Effects, Standards and Guidelines

Surface Water in 2010 near Dresden NPP8 Bq L-1


14C Health Effects

• 14C is uniformly distributed in body

• Energy distribution is the same as chronic, uniform irradiation from 60Co; therefore, the health effects are predicted to be the same

• Because of this, long term health effects studies in large animals have not been done


Health Effects of Iodine-131

• Iodine-131 concentrates in the Thyroid• Short half-life results in high doses • Chernobyl had very large doses (>1 Gy) of Iodine-131 to a

large population (tens of thousands of children)• Increased frequency of thyroid cancers in children exposed

(~4,000 excess thyroid cancers)• Less than ten thyroid cancer deaths


Dose and health effects of Cesium-137

• Long physical half-life and short effective half-life•Uniformly distributed in the body and results in a whole body dose

•Major component of fallout from nuclear weapons•Concentrates up the food chain•Cesium binds to clay particles making it less biologically available


Open Questions

• Can the major difficulties with studies (e.g. the selection of representative controls and the adjustment for confounding) be overcome?

• Little indication that the risk per unit dose for childhood leukemia has been seriously underestimated.

• Little indication that the risk of childhood leukemia arising from exposure to anthropogenic radionuclides has been seriously underestimated.

• Given this, what are the proposed studies expected to show with respect to radiation risk?

• Environmental measurements (e.g. of long-lived radionuclides in tree-rings or human urine) could be useful in validating discharge histories.

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