“Health Physics Archeology” An Overview of Dose Reconstruction Radiation Studies Branch National Center for Environmental Health Centers for Disease Control and Prevention August, 2004
Outline • Overview of dose reconstruction principles • Examples of CDC dose reconstruction projects • Lessons learned from dose reconstruction projects
Dose Reconstruction Dose reconstruction is a comprehensive analysis of the exposure received by individuals in the vicinity of facilities that release contaminants to the environment (i.e., real doses to real people).
“Health Physics Archeology” Dose Reconstruction
Purpose of Dose Reconstruction • Provide a comprehensive history of site operations, including releases of radioactive material. • Provide dose distribution estimates used in epidemiological studies. • Provide an independent, comprehensive evaluation of risk. • Provide a baseline for analyzing effects of other activities (e.g., clean-up).
Major Goals of Dose Reconstruction • Assure the soundness of the science • Gain public acceptance No matter how good the science, if the public does not accept the results, we fail.
Basic Assumptions • No standard methodological guide book exists. • Each site has uniqueattributes. • Lessons can be learned from each study. • Common approaches can be developed.
Dose Reconstruction Process 1. Retrieval and assessment of data 2. Development of initial source term and pathway analysis 3. Calculation of screening doses and exposures 4. Development of methods for assessing environmental doses 5. Calculation of environmental exposures, doses, and risks
Stages of the Process • Stages of the process may overlap in time. • Stages may be performed iteratively. • All stages may not be necessary at all sites. • Total process at each site may take 4–7 years or more to complete.
Preliminary Analysis • Assess the amount of public interest. • Conduct a literature review of all research in a related area. • Gather all relevant dataand recordsfor the particular site. • Conduct personal interviews.
Dose Assessment Three Levels: • Preliminary (Scoping Study) • Comprehensive Analysis • Individual Dose Assessment
New Dose Assessment Paradigm If risk = health effect, conservative dose estimates of dose will be nonconservative for epidemiology
Preliminary Dose Assessment Scoping Study– A preliminary analysis used to determine whether a comprehensive dose reconstruction study is appropriate as the basis for a continued comprehensive epidemiological study
Variables in a Scoping Study Conditions of the Release: • Chemical and physical form • Time dependence Conditions of the Environment: • Geographical • Agricultural • Meteorological
Variables in a Scoping Study (continued) Conditions of the Population: • Size • Diversity • Structure • Human interactions
Variables in a Scoping Study (continued) Statistical Requirements: • Availability and quality of records • Doses that can be estimated • Large population size
Analysis of Scoping Study Results Based on the outcome of the scoping study, the project may come to halt or proceed to a full dose reconstruction.
Comprehensive Dose Assessment Estimation of: • the source term – amount of radionuclides or chemicals released from a site to the environment during a specific period) • both internal and external sources of radiation encountered by human beings
Comprehensive Analysis Ways to determine and estimate the source term: • Engineering estimates • Historic reports of measured releases • Reconstruction Redundant analyses are desirable.
Individual Dose Assessment • Variables that may affect individual risk must be recorded, such as gender, age, size, lifestyle, and diet. • Children are often the most affected population.
Gathering Data: Criteria • Measured (quantitative) • Described in understandable units • Raw data required (not summaries, reports, or interpretations) • Withstand scientific scrutiny • Unbiased • Recorded by specialists or experienced staff
Gathering Data: Source Preferences • Interviews of reliable witnesses • Data sheets (e.g., sample mass, activity, or concentration measurement records) • Logbooks • Incident reports • Production reports • Safety organizations
Data Collection and Analysis Data could be missing because of: • Loss • Destruction • Considered obsolete • Concern about security Models must be developed to extrapolate missing data.
Other Data Complications Data may be recorded from releases that are: • Episodic – lasting ≤ 10 days • Chronic – recurring over a period of time • Accidental – resulting from a single unexpected incident
Uncertainty Analysis Quantification of the extent of uncertainty in the model from all conceivable sources. Involves propagation of uncertainty in the input parameters and the methodology. Often expressed as a ‘confidence interval.’
Sensitivity Analysis Evaluation of the extent to which changes in values of independent variables (or model parameters) of an equation (or mathematical model) bring about changes in the results. Allows identification of the parameters that dominate the overall uncertainty in the model.
Dose Reconstruction and Epidemiology After completion of dose reconstruction, the information can be used as input in an epidemiological study.
Epidemiology The study of disease in human populations
Objectives of an Epidemiological Study Questions used to determine objectives: • What is the most likely radiation exposure in the community? • What health effects have been reported from similar exposures? • What concerns are expressed by the community?
Epidemiological Studies Case-Control Study • Compares two groups: - one group with the health effect to - one group without the health effect. • Differences between the two groups that may have caused the health effect are then determined.
Epidemiological Studies (continued) Prospective Study • Follows two groups through time: - exposed group - not exposed group. • Compares disease rates between the two groups.
Epidemiological Studies (continued) Cohort Study • Exposed group is studied. • Exposed group's disease rates are compared to expected rates. Many radiation-related epidemiological studies are cohort studies.
Type of Cohort Study: Dose Response Disease Dose
Strong Dose Response Disease Dose
Weak Dose Response Disease Dose
No Dose Response Disease Dose
Feasibility Analysis In order to determine the feasibility of an epidemiological study, the statistical power of the study must be high enough to identify an increased risk for health effects if one exists.
Statistical Power Probability that the study can distinguish between a true exposure-to-disease relation and a coincidence
Statistical Power The variables for statistical power are: • Size of population • Amount of exposure • Expected strength of association between exposure and disease • Number of cases of disease under investigation
CDC’s Dose Reconstruction Projects • 1990 − Memorandum of Understanding (MOU) was signed between Departments of Energy (DOE) and Health and Human Services (HHS). Renewed in 1995 and 2000. • MOU transferred energy-related epidemiological research program from DOE to HHS. CDC designated as lead agency for HHS.
CDC’s Dose Reconstruction Projects • National Center for Environmental Health (NCEH) coordinates program and conducts environmental health studies. • National Institute of Occupational Safety and Health (NIOSH) conducts worker health studies. • The Agency for Toxic Substances and Disease Registry (ATSDR) conducts work related to Super Fund sites.
Dose Reconstruction Activities Hanford Idaho National Engineering & Environmental Laboratory Ashtabula Lawrence Mound Livermore Nevada Rocky Flats Fernald Bendix Portsmouth Test Site Paducah Oak Ridge Los Alamos Pantex Savannah River Site Sandia Republic of the Marshall Islands Pinellas Current Activities Technical Support No Current Involvement Activities Complete
Fernald, Ohio • 1951–1988: Site produced uranium feed materials. • 1990: CDC began dose reconstruction project. • 1998: CDC released final reports on the dose reconstruction issued (radon and uranium primary radionuclides). • 1998–1999: CDC performed a risk analysis for lung cancer. • June 1999: CDC presented a screening analysis for other cancers. • Currently: No additional studies planned.
Hanford, Washington • 1944–1990: Site produced plutonium. • 1987: CDC began epidemiological project. • 1994: CDC released primary results of Hanford Environmental Dose Reconstruction (HEDR). • 1998–2000: Washington, Oregon, & Idaho provided individual I-131 dose estimates for exposed people using HEDR models. • 2002: Hanford Thyroid Disease Study completed.
Hanford, Washington (continued) Currently: • Follow-up of Columbia River dose reconstruction • Development of a computer program to estimate doses from radioactive particles and short-lived radionuclides • Development of Web-based individual dose assessment tool
Idaho National Engineering and Environmental Laboratory (INEEL) • 1949: Site began operation as a National Reactor Testing Station. • 1992: CDC began dose reconstruction project. • 1995: CDC issued 2 reports on Phase I (document search & database development). • October 2002: CDC completed preliminary studies of chemical and radionuclide releases. • Currently: CDC is performing radionuclide dose reconstructions for selected years at Idaho Chemical Processing Plant and screening calculations at the Aircraft Nuclear Propulsion Program.
Los Alamos National Laboratory (LANL) • 1998: CDC began Los Alamos Historical Documents Retrieval and Assessment (LAHDRA) Project. • Documents will be retrieved and evaluated for their usefulness for offsite dose assessment. • Relevant documents will be declassified, copied, and made available to the public. • Relevant documents will be entered into an electronic database. • Prioritized list of contaminantreleases from the LANL site will be developed.
Republic of the Marshall Islands (RMI) • 1946–1958: RMI was the site of 69 U.S. nuclear weapons tests. • CDC completed a cooperative agreement with the RMI government for • methods development and validation work for cesium deposition and • soil analysis for iodine-129.