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Organization of a national comparison for activity determination of 99mTc in nuclear medicine

15.01.2007

In nuclear medicine, the short-lived radionuclide 99mTc is often used for diagnostic purposes. Before radiopharmaceuticals with 99mTc are administered to patients, the activity is determined - normally with ionization chambers, which are frequently also referred to as radionuclide calibrators or activity meters. A reliable activity determination is very important as, on the one hand, a reliable diagnostic result is to be obtained and, on the other hand, too high radiation exposures burden of the patient must be prevented.

In the period under report, the Physikalisch-Technische Bundesanstalt (PTB) has organized, in cooperation with QSA Global GmbH, Braunschweig, a national comparison with 99mTc solutions. For this purpose, the participants from hospitals and nuclear-medical practices received aliquots of 99mTc solutions, whose activity reference values were determined by measurements at PTB. The participants were asked to determine the activity unknown to them and to enter the data obtained in a questionnaire, together with information regarding the devices used, the uncertainties, possibly detected radioactive impurities as well as additional measures taken for quality assurance. Subsequently, all questionnaires were evaluated at PTB, and a detailed result report will soon be published. Finally, all participants obtained a calibration certificate of PTB and can thus check their result and eventually take additional quality assuring measures.

The 52 participants reported 100 results from measurements on the type P6 glass ampoules made available and, in addition, 95 results from measurements performed after the solution had been transferred to syringes. Approx. 92% of the measurement results in glass ampoules deviate by less than 10% from the reference value and thus meet a criterion required in the European Pharmacopoeia [1]. This represents a clear improvement compared to early comparison measurements [2-3]. Moreover, the data were investigated to detect possible causes of discrepancies. Here it turned out that in many cases large deviations are not due to the measuring devices, but to insufficiently qualified staff. Some deviations can, for example, be explained by the fact that the activity values determined were not corrected or corrected in an incorrect way with respect to the radioactive decay.

In addition, PTB has sent parts of the 99mTc solution to the Bureau International des Poids et Mesures, to meet the challenge of a comparison within the scope of the International Reference System (SIR). The activity value of PTB determined with small uncertainty is in very good agreement with the key comparison reference value (KCRV) which is obtained from the results of 4 National Metrology Institutes.

Literature

  1. European Pharmacopoeia, European Directorate for the Quality of Medicines (EDQM), 5th ed. (2005), Strasbourg.
  2. Debertin, K., Schrader, H.:
    Intercomparisons for quality assurance of activity measurements with radionuclide calibrators.
    Nucl. Instr. Meth. A312 (1992) 241.
  3. Rodloff, G., Schrader, H., Thieme, K.:
    99Tcm-Vergleichsmessungen mit Aktivimetern.
    Der Nuklearmediziner 5, 17, (1994) 399.