RT Journal Article
SR Electronic
T1 Development of a Traceable Calibration Methodology for Solid <sup>68</sup>Ge/<sup>68</sup>Ga Sources Used as a Calibration Surrogate for <sup>18</sup>F in Radionuclide Activity Calibrators
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 448
OP 453
DO 10.2967/jnumed.109.070300
VO 51
IS 3
A1 Brian E. Zimmerman
A1 Jeffrey T. Cessna
YR 2010
UL http://jnm.snmjournals.org/content/51/3/448.abstract
AB We have developed a methodology for calibrating 68Ge radioactivity content in a commercially available calibration source for activity calibrators in a way that is traceable to the national standard. Additionally, the source was cross-calibrated for equivalent 18F content by direct comparison with the national standard for 18F in the same geometry. Methods: Sources containing standardized 68GeCl4 or 18F-FDG solutions were prepared at the National Institute of Standards and Technology (NIST) with mock syringe blanks used in the construction of a commercially available epoxy-based 68Ge calibration source. These sources and several NIST-constructed epoxy-based 68Ge mock syringes were then used as artifact standards to determine calibration factors for NIST-maintained activity calibrators and secondary standard ionization chambers to enable calibration of the actual commercial sources. A direct comparison between the solution-based 68Ge sources and the 18F-FDG sources allowed for an empiric determination of the relative response for these radionuclides in several commercial activity calibrators. Potential measurement effects due to differences between the solution composition and the epoxy and theoretic 68Ge-to-18F response ratios were studied by Monte Carlo simulation. Results: The calibration factors developed in this study enabled NIST to calibrate epoxy-based mock syringe sources with a relative combined standard uncertainty of 0.52%. The direct comparisons of the 68Ge and 18F standards in the various ionization chambers allowed the activity to be expressed in terms of equivalent 18F activity with a relative combined standard uncertainty of about 0.9%. Conclusion: The ability for NIST to calibrate these epoxy-based mock syringes enabled, for the first time to our knowledge, the direct traceability to the national 68Ge standard to be established for this type of source. Through a direct comparison with the NIST 18F standard, the determination of the relative response ratios in activity calibrators enabled the equivalent 18F activity to be determined in a way that was also traceable to the national 18F activity standard.