Radioisotope calibrators are used to assay vials and syringes containing radioactive isotopes before administration to patients.
High accuracy and repeatability are two essential characteristics of PET radioisotope calibrators.
Facilities should choose a radionuclide dose calibrator based on the range and type of isotopes that will be assayed and the level of automation required.
The more advanced radioisotope calibrator units offer buyers more calibration factors built-in and more automated documentation features.
Facilities should also consider the amount of built-in lead shielding when purchasing a radioisotope calibrators. Higher energy and higher activity isotopes may require more lead shielding than is built in. Additional shielding with specially designed lead blocks can be added.
The operating environment immensely affects the radionuclide dose calibrator performance. Therefore, buyers are encouraged to evaluate radioisotope calibrator performance on-site for linearity, geometric variation, accuracy, and constancy, and compare the findings with the manufacturer's specifications. These tests should be performed prior to putting a new unit in service, after repair, and at regular intervals.
Sample container, sample position within the well, and sample volume are all responsible for the radionuclide dose calibrator response to differences in sample geometry.
Depending on whether the sample is in a vial or a syringe, the readouts of equal activities can differ. Readings of 125I and 133Xe are known to vary widely, depending on the container used, and usually require a correction factor to compensate for the differences.
Plastic sample holders and deep-well detectors have eliminated the adverse effects of varying sample positions within the well. Deep wells best approximate 4 geometry, the best situation in which the sample is completely surrounded by the sensitive volume of the ionization chamber.
A standard with a long half-life, such as 137Cs, is the best for measuring radioisotope calibrator constancy. Sample readings of the same source taken at 24-hour intervals should agree within 5%.
To determine the PET radioisotope calibrator accuracy, the certified activity of a traceable standard is measured. The average of three consecutive readings should match the certified activity within 5%. Users should repeat the test for standards of various energies.
The overall accuracy depends on the combined accuracy of the detector, the electrometer, the digital readout, and the traceable standard.

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