Improvements in In-Vivo Radionuclide Metrology

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Objectives for MPD C.4.4

  • Improve the consistency of measurements for internal radioactivity depositions in humans resulting from occupational or natural exposure.
  • Develop techniques that can detect and measure lower concentrations of radionuclides in organs and soft body tissues.

Background: Non-invasive in vivo and in-vitro radiobioassay (whole-body and organ counting, and urine, feces and tissue radioanalysis, respectively) of personnel working with radionuclides or materials with potential radioactive contamination is a primary method dosimetrists employ for routine occupational monitoring and accident assessment.

The variability among “homemade” and de facto reference phantoms can account for up to an 80% difference among measurement laboratory results [Kramer, G. H., Loesch, R. L., and Olsen, P. C. “The Second International In-Vivo Intercomparison Program for Whole Body Counting Facilities by Canadian and United States Agencies;” Health Physics 80(3), 214-224 (2001)]. Measurement com¬parability and consistency can be ensured through calibrations based on national standard realistic human-surrogates (calibration phantoms). In addition, site-specific (organ specific) quantitative assessment requires new measurement technology and 3 D tomography. A solution to the problem of measurement differences is the continued development of technological and measurement quality assurance bases for quantitative site-specific in vivo radio¬bioassay. This is a recommendation of the International Workshop on Standard Phantoms for In Vivo Radioactivity Measurements [Health Physics, 61, 893 (1991)].

Similarly, the variability of in-vitro radiobioassay measurements is largely due to sampling heterogeneity and non-equilibrium of chemical yield monitors with the analytes of interest during sample preparation. While sample heterogeneity problems may be improved by taking larger or more samples, problems of completely equilibrating the chemical yield monitors with the analyte in the sample is largely dependent on the chemical speciation of the analyte. For example, refractory plutonium particles in the lung or in fecal samples could be underestimated by 15-50 percent if insufficiently aggressive dissolution methods were used. Even in cases where the analyte is easily solubilized, precision of analysis of radionuclides in synthetic urine and fecal test samples is of the order of 10-15 percent (Wu,, BERM Conference Proceedings). To improve these capabilities, there is a need for the development of new reference materials and traceable Proficiency Testing programs to continue to evaluate and improve the measurement community’s capabilities.

Action Items:

1 – Develop calibration systems and quality assurance protocols for radionuclide-labeled organ and phantom surrogates.

2- Facilitate comparison of cali¬brations with standard phantoms to surrogates in the DOE phantom library and to real animal/human exposures in order to improve measurement techniques and measurement consistency.

3 – Develop 3-D tomography and related computational methods for improved definition of organ/tissue modeling.

4 – Evaluate long-term massic activity stability of radionuclides in synthetic urine and fecal test samples.

5 – Develop certified high fired plutonium performance test samples.

6 – Extend bioassay accreditation programs, possibly through the HPS accreditation program, beyond the current DOE RESL program.

Resource Requirements:

1 – A cumulative expenditure of approximately $3million over the next three-year time frame will be needed to sustain and properly coordinate efforts at NIST, LLNL, the Bureau of Radiation and Medical Devices (BRMD), RESL and PNNL on new phantom materials, ANSI and international standards, techniques for assessing homogeneity and content of phantom inserts, and Monte Carlo calculations.

2 - An investment of 1 FTE to evaluate the long term stability of the synthetic urine test samples, and develop the reliable production and certification of refractory plutonium in bioassay test samples.

3 – Investigation of extending accreditation efforts to sectors other than DOE will require a minimum of 20% of a person year of effort.