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Whole-Body Counting

What is Whole Body Counting? | What Will Whole Body Counting Show? | Estimating Doses from Cesium-137 Based on Whole Body Counting | Performance Evaluation of the Whole Body Counting Program | Summary Results Enewetak Island Residents | Summary Results Rongelap Resettlement Workers | Summary Results Utrōk Population Group as well as for other Marshall Islanders

What is Whole Body Counting?

The whole body counting systems installed in the Marshall Islands contain large volume sodium iodide radiation detectors that measure gamma rays coming from radionuclides deposited in the body. The detector systems are modeled after the Masse-Bolton Chair design (Figure 8), and can be used to detect high-energy gamma-emitting radionuclides such as cesium-137 and cobalt-60 in most of the body and all of the internal organs. Using established procedures, the whole body counting measurement data are converted into an annual effective dose using specially designed computer software (Canberra, 1998a; 1998b) and a dose report issued to program volunteers immediately following the measurement.

There are currently three operational whole body counting facilities in the Republic of the Marshall Islands. These facilities are located on Enewetak, Rongelap and Majuro Atolls. The whole body counting systems are calibrated using a mixed-gamma point source. The point source calibration procedure was developed by cross-reference to a Bottle Man-akin Absorption (BOMAB) phantom (or human surrogate) calibration source containing a standard mix of gamma-emitting radionuclides traceable to the U.S. National Institute of Standards and Technology (NIST).

Wherever possible, the whole body counting program in the Marshall Islands is conducted using the same quality requirements as established under the U.S. Department of Energy Laboratory Accreditation Program (DOELAP) for internal dosimetry. Systems background and other quality control check counts are performed on a daily basis to ensure that the measurement system conforms to all applicable quality requirements. Also, the Livermore under the Marshall Islands Program. whole body counting facilities participate in performance testing under the umbrella of the Oak Ridge National Laboratory Intercomparison Studies Program (ISP). These performance test samples are distributed around each of the facilities including a mirror whole body counting system located at

The performance of each facility is then evaluated by comparing results with those obtained by the Hazards Control Department at the Lawrence Livermore National Laboratory-a DOELAP accredited facility-and with the reference values supplied by the Oak Ridge National Laboratory. Based on our external quality assurance program, the Marshall Island Program whole body counting facilities have consistently conformed to the ANSI 13.30 criteria for accuracy and measurement precision (Kehl et al., 2007).

Local Marshallese technicians are responsible for all daily operations within the facilities including scheduling of personal counts, performing systems performance checks, data reduction, and initial reporting of dosimetric data to program volunteers. The technicians receive an initial six weeks of intensive training at the Lawrence Livermore National Laboratory and are employed to run the facilities for up to 40 hours per week. Scientists from the Lawrence Livermore National Laboratory provide on-going technical support services, advanced training in whole body counting and basic health physics, and perform a more detailed data quality assurance appraisal before any data are released in reports or posted on the Marshall Islands web site.



Figure 8:  


The Rongelap whole body counter with a volunteer seated in the chair (used with permission).



What Does Whole Body Counting Show?

The main pathway for exposure to residual fallout contamination in the northern Marshall Islands is through ingestion of cesium-137 contained in locally grown foods such as coconut, Pandanus fruit and breadfruit (Robison et al., 1997a). The strategic objective of the Marshall Islands Whole Body Counting Program is to offer island residents an unprecedented level of radiation protection monitoring until such time that it is clearly demonstrated that radiation surveillance measures can be relaxed. The value of this type of radiation protection monitoring program lies in the fact that whole body count data provides a direct measure of radionuclide uptake into local populations. Information about potential high-end health risks and seasonal fluctuations in the body burden of cesium-137 within various Marshallese atoll population groups can be assessed from repeated measurement data rather than relying on a range of assumptions from different dietary scenarios.

In combination with environmental monitoring data, residents who receive a whole body count showing the presence of cesium-137 can now make an informed decision about their eating habits or life-style based on what is considered a ‘safe’ or acceptable health risk. The Republic of the Marshall Islands Nuclear Claims Tribunal has adopted a standard for cleanup of radioactively contaminated sites of 0.15 millisievert (mSv) per year (or 15 mrem per year) [EDE, Effective Dose Equivalent] using a lifetime cancer risk criterion recommended by the United States Environmental Protection Agency (EPA). As displaced communities return to their ancestral homelands, the Marshall Islands Whole Body Counting Program will allow the United States Department of Energy to monitor the resettled population on Enewetak and provide assurances that radiation related health risks remain at or below these established standards.


Estimating Doses from Cesium-137 Based on Whole Body Counting

People living in the Marshall Islands may be exposed to cesium-137 contained in their diets from eating locally grown food crop products, such as coconut. Whole body counting provides a direct measure of the amount of cesium-137 inside the body of people. The biokinetic behavior of cesium-137 inside the human body is well known and allows information from the whole body counter to be converted to a radiation dose. The radiation dose is what is used to quantify the potential health risks associated with radiation exposure. The dosimetric data graphics displayed on this web site are based on the calendar year committed effective dose equivalent (CEDE) from intakes of cesium-137 in the year of measurement projected over 50 years (Daniels et al., 2007). Dose equivalent is given in units of rem, the conventional units used by federal and state agencies in the United States. The SI unit of dose equivalent is the joule per kilogram or sievert (Sv). Doses from exposure to environmental radioactivity (natural or manmade) are normally expressed as 1/1000th of the base unit, i.e., in millirem (mrem) or millisievert (mSv). 1 mSv is equal to 100 mrem.

Information Note: The methodologies for computing doses from the whole body counting and plutonium urinalysis programs have recently been outlined in a Technical Basis Document, see Daniels et al., 2007. As compared to previous upgrades of this web site, this new methodology uses a 50-y dose commitment and complies more fully with ICRP methodology. The algorisms developed to allow users to compute doses directly from measurement data made available on this web site are also consistent with this new methodology.



Performance Evaluation of the Whole Body Counting Program

Whole Body counting facilities in the Marshall Islands as well as a mirror facility maintained at the Lawrence Livermore National Laboratory participate in bi-annual performance evaluation exercises conducted under the umbrella of the Oak Ridge National Laboratory Intercomparison Studies Program (ISP). The ISP was specifically designed to support the United States Department of Energy Laboratory Accreditation Program (DOELAP). In this way, the Marshall Islands Radiological Surveillance Program has established quality assurance measures that are consistent with standard requirements used to monitor DOE workers in the United States.

The performance evaluation samples for whole body count measurements are prepared in a mock-up geometry that simulates a human body torso, and usually contains a mix of barium-133 (133Ba), cobalt-60 (60Co), cesium-137 (137Cs) and yttrium-88 (88Y) isotopes at nominal concentrations of ≤ 18.5 kBq (or 500 nCi) per sample. The ISP at Oak Ridge use stock isotope solutions indirectly traceable to the National Institute of Standards and Technology (NIST). Details concerning the NIST stock solutions and ISP spikes used in the preparation of the whole body count performance evaluation samples can be found elsewhere (ISP Report, 2005). For practical purposes we have limited performance evaluation testing of the Marshall Island whole body counting facilities to detection and measurement of cesium-137.

For testing purposes, the relative bias (%, Bri) for a whole body count measurement (i) shows how close the measured activity is to the reference (known) value of the test sample. The relative bias (%, Br) for any whole body count facility can then be calculated as the average of the individual relative biases Bri as defined as the following, where N is the number of measurements performed within each facility:

The mean relative bias statistic for the LLNL, Rongelap, Enewetak and Utrōk (Majuro) facilities based on performance evaluation exercises conducted between 2002 and 2005 was 25%, 15.4%, 19.6%, and -5.4%, respectively. This compares with ANSI 13.30 acceptance criteria used in the United States for radiobioassay service laboratory quality control, performance testing, and accreditation of -25% to +50%. The results for each performance evaluation exercise conducted between 2002 and 2005 are shown graphically in Figure 9 with the upper (UCL) and lower LCL) control limits.



Figure 9:  


Multivar gage plot showing performance of whole body counting facilities for biannual performacne evaluation exercises (2002 throught 2005).



The relative precision (%, SB) of the measurements performed across each whole body count count facility is the relative dispersion of the values of Bri from their mean Br, and is defined as:



The acceptance criteria for the relative measurement precision statistic (SB) based on the ANSI 13.30 standard criteria for radiobioassay service laboratory quality control, performance testing, and accreditation is less than or equal to 40%. The mean relative precision statistic for the LLNL, Rongelap, Enewetak, and Utrōk (Majuro) facilities based on performance evaluation exercises conducted between 2002 and 2005 was 8.9%, 1.6%, 9.5%, and 16.7%, respectively.

The combined mean relative bias and relative precision statistic across all the Marshall Islands whole body counting facilities was 12.6% and 20.5%, respectively. Consequently, whole body count facilities in the Marshall Islands have consistently passed ANSI 13.30 performance criteria for relative measurement bias and precision.



Doses from Internally Deposited Cesium-137 Delivered to Residents and Visitors on Enewetak Island

The individual dosimetric data from the whole body counting program (2005-06) are available on this web site [Chick here to view (de-identified) dosimetric and measurement data].

A probability distribution plot of the committed effective dose equivalent delivered to program volunteers on Enewetak Island from internally deposited cesium-137, annualized to the year of measurement, is shown in Figure 10.



Figure 10:  


Dose distribution plot of the committed effective dose equivalent delivered to Enewetak Atoll residents (2005-2006) from internally desposited cesium-127, annualized to the measurement year.



The majority of people living on Enewetak Island received internal doses from intakes of cesium-137 of less than 1 mrem (0.01 mSv) per year (Figure 10). The population average committed >effective dose equivalent averaged over the past two years was 0.7 ± 0.8 mrem (N=368). This compares with population average doses of 0.5 ± 0.5 mrem reported for 2001 (N = 417), 0.8 ± 0.8 mrem in 2002 (N=131), 0.5 ± 0.7 mrem in 2003 (N = 197) and 0.7 ± 1.3 mrem in 2004 (N = 316). The corresponding maximal individual committed effective dose equivalent reported for each measurement year since the introduction of this radiological surveillance monitoring program are 3.2 mrem (2001), 4.9 mrem (2002), 4.0 mrem (2003), 11.5 mrem (2004), 3.5 mrem (2005), and 3.4 mrem (2006). It should be noted that the body burden of cesium-137 in about 1 of every 4 individuals on Enewetak Island falls below the >critical level of the measurements (Lc ~ 0.05 kBq) and, for the purposes of calculating summary statistics, was assigned a dose equal to zero.



Summary

The committed effective dose equivalent delivered to Enewetak Atoll residents (including some short-term visitors) from ingestion of cesium-137 can be compared with the natural background effective dose equivalent (EDE) of 140 mrem per year in the Marshall Islands and 300 mrem per year in the United States. The observed internal doses from cesium-137 for all program volunteers on Enewetak are also significantly lower than the annual dose criteria of 100 mrem per year, excluding medical irradiation, imposed in 10CRF Part 20 (NRC, 2004) for protection of the public. Consequently, the results of the whole body counting program clearly demonstrate that Enewetak residents are not being exposed to significantly elevated levels of cesium-137 in their diet. However, we recognize that people of Enewetak Atoll only receive periodic shipments of imported foods and during short shortages or during festive events may consume more foods from the northern islands where levels of fallout contamination are considerably higher. Moreover, as population dynamics on the atoll change there may be more pressure on the community to make wider use of resources across the entire atoll. The continuing whole body counting program on Enewetak Island will also ensure that people who occasionally binge on foods from the northern islands are carefully monitored. Under these circumstances, the annual dose delivered to an individual may be dominated by intakes of cesium-137 from occasional visitations to the northern islands where local terrestrial foods typically contain higher average concentrations of cesium-137 (as well as other fallout radionuclides).



Doses from Internally Deposited Cesium-137 Delivered to Residents and Visitors on Rongelap Atoll

The individual dosimetric data from the whole body counting program on Rongelap Island are available on this web site [Chick here to view individual (de-identified) dosimetric and measurement data].

A probability distribution plot of the committed effective dose equivalent delivered to program volunteers on Rongelap Island from internally deposited cesium-137, annualized to the year of measurement, is shown in Figure 11.



Figure 11:  

Dose distribution plot of the committed effective dose equivalent delivered to Rongelap resettlement workers (2005-2006) from internally deposited cesium-137, annualized to the year of measurement.



Summary

The committed effective dose equivalent for internally deposited cesium-137 in resettlement workers and other visitors to Rongelap can be compared with the natural background Effective Dose Equivalent (EDE) of 140 mrem per year in the Marshall Islands and about 300 mrem per year in the United States. The observed internal doses from cesium-137 for all program volunteers on Rongelap was also significantly lower than the annual dose criteria of 100 mrem per year, excluding medical irradiation, imposed in 10CRF Part 20 (NRC, 2004) for protection of the public. Consequently, the results of the whole body counting program on Rongelap clearly demonstrate that resettlement workers are not being exposed to significantly elevated levels of cesium-137 in their diets. However, permanent residents living on Rongelap Atoll are more likely to adopt a traditional lifestyle and consume larger quantities of locally grown foods. Accordingly, we recommend that similar action be taken in developing a whole body counting program to monitor the return of the resettled population.



Doses from Internally Deposited Cesium-137 Delivered to the Utrōk Population Group as well as to other Marshall Islanders

The individual dosimetric data from the whole body counting program on Majuro Atoll are available on this web site [Chick here to view individual (de-identified) dosimetric and measurement data].

Probability distribution plots of the committed effective dose equivalent from internally deposited cesium-137 delivered to the Utrōk Atoll population group as well as for other program volunteers in the Marshall Islands, annualized to the year of measurement, are shown in Figure 12a and Figure 12b. The Utrōk Atoll cohort group has been subdivided into those program volunteers who reside on Utrok Atoll and those who live elsewhere in the Marshall Islands, largely on Majuro Atoll. Similarly, the Marshall Islands cohort group has been subdivided into those program volunteers who reside in the northern Marshall Islands and those who live on the southern atolls (including Majuro).



Figure 12a:  

Dose distribution plots of the committed effective dose equivalent from internally deposited cesium-137 delivered to the Utrōk Atoll population group, annualized to the year of measurement.



Figure 12b:  

Dose distribution plots of the committed effective dose equivalent from internally deposited cesium-137 delivered to other program volunteers in the northern and southern Marshall Islands, annualized to the year of measurement.



The population average committed effective dose equivalent for program volunteers living on Utrōk Atoll averaged over the past two years was 3.5 ± 2.0 mrem (N=74) (Figure 12a. This compares with population average doses observed for this same resident population group during 2003 and 2004 of 1.6 ± 1.4 mrem (N=25) and 3.0 ± 1.8 mrem (N=21), respectively. As observed in previous years, most people from the Utrōk population group who were resident on Majuro Atoll or elsewhere in the southern Marshall Islands did not acquire a measurable body burden of cesium-137.

Similarly, the population average committed effective dose equivalent for program volunteers living elsewhere in the northern Marshall Islands over the past two years (excluding Enetwetak and Utrōk residents, and resettlement workers and visitors on Rongelap Atoll) was 1.6 ± 1.6 mrem (N=33) (Figure 12b). The vast majority of these program volunteers came from Ailuk and Likiep Atolls. The corresponding population average committed effective dose equivalent for program volunteers living on southern atolls was >0.1 mrem (N=287). It should be noted that the body burdens of cesium-137 measured in most volunteers from that southern atolls (including Majuro Atoll) were below the critical level of the measurements (Lc ~ 0.05 kBq) and, for the purposes of calculating summary statistics, was assigned a dose equal to zero.

Although the whole body burdens of cesium-137 are generally low and equate to annualized dose contributions of less than 5 mrem, these data do show than people living on Utrōk Atoll and elsewhere in the northern Marshall Islands are more likely to acquire measureable doses from internally deposited cesium-137.



Summary

The committed effective dose equivalent from internally deposited cesium-137 within the Utrōk Atoll population group as well as for other program volunteers can be compared with the natural background Effective Dose Equivalent (EDE) of 140 mrem per year in the Marshall Islands and 300 mrem per year in the United States. Internal doses from internally deposited cesium-137 for all program volunteers independent of where they live is also well below the annual dose criteria of 100 mrem per year, excluding medical irradiation, imposed in 10CRF Part 20 (NRC, 2004) for protection of the public. The Republic of the Marshall Islands Nuclear Claims Tribunal has adopted a standard for cleanup of radioactively contaminated sites in the Marshall Islands of 15 mrem (0.15 mSv) per year. With the knowledge that cesium-137 ingestion is a major contributor to dose from exposure to residual fallout contamination in the Marshall Islands, data derived from the whole body counting program provides a direct measure of doses delivered to program volunteers under present-day conditions for comparison to applicable cleanup standards or guidelines. The results from the whole body counting program on Majuro appears to demonstrate that residents living on Utrōk Atoll are not being exposed to significantly elevated levels of cesium-137 in their diets. It is, however, recommended that the monitoring program be continued in order to accurately assess doses based on population group, age, and gender, and to identify potential individuals at higher risk from radiation exposure, especially in relation to people living in the northern Marshall Islands.



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