Effects of varying geometry on dose calibrator response: cobalt-57 and technetium-99m

A joint project between the National Bureau of Standards (NBS) and Biomedical Products Department, E.I. du Pont de Nemours and Company, Inc. compared the indicated activity of (a) cobalt-57 samples in NBS 5-ml ampoules, plastic syringes, Du Pont 27-ml Vial E epoxy- and solution-filled containers, and (b) technetium-99m solutions in NBS 5-ml ampoules, elution vials, and syringes. The measurements were made in ionization chambers from two manufacturers, Capintec and Radcal. The main objective was to examine the use of radionuclides in NBS ampoules and Du Pont Vial E containers as suitable reference sources for ionization chambers used to assay radiopharmaceuticals in elution vials and syringes. The exercise illustrated that regardless of the brand of dose calibrator used, a calibration factor for each geometry should be determined to ensure the highest accuracy. The data show that as much as a 9% difference from the correct activity can be observed for these radionuclides, even when the ampoule reference source gives the appropriate reading.