Accuracy Testing of Dose Calibrators

Abstract

Current methods for testing a dose calibrator’s accuracy use measurements of ⁶⁰Co, ¹³⁷Cs, ⁵⁷Co, and ¹³³Ba sources but do not directly measure the accuracy of clinical radionuclides such as ^99mTc, ¹²³I, ¹¹¹In, ⁶⁷Ga, or ²⁰¹Tl. It is possible that some dose calibrators inaccurately determine the activity of these clinical radiopharmaceuticals. To correct this possible deficiency, we have devised a method to test the accuracy of each radionuclide setting on a dose calibrator using a single long-lived calibration source. Differences in emission characteristics of assayed radionuclides are incorporated in the ionization current-to-activity conversion factors (CAF) that are determined experimentally by the manufacturer. The correct functioning of a dose calibrator requires that each CAF be accurately reproduced electronically by the calibrator circuitry and that the measured ionization current be consistent and precise. Our results have shown that our procedure tests the total function of the dose calibrator for detecting all radionuclides specified by the manufacturer including the accuracy of the electronic representations of the CAF. The procedure is easily implemented for all dose calibrator systems using one of several possible sources available in most laboratories (e.g., ⁵⁷Co, ¹³⁷Cs, or ¹³³Ba).