Quality control of dose calibrator using a traceable syringe-type 68Ge/68Ga calibration source

Accurate calibration of dose calibrators (DC) is required for quantitative positron emission tomography (PET) studies to generate meaningful information. Values measured by DC depend not only on the radioactive nuclide but also the environment where measurements are taken. Therefore, DC must be calibrated at each location. The present study aimed to determine appropriate calibration values, and evaluate the performance of DC using a traceable 68Ge/68Ga calibration source that is available as a surrogate 18F source. We used a 68Ge/68Ga calibration source to determine the optimal DC value for measuring 18F activity in the operating environment. Variations in sensitivity and geometry as well as measurement uncertainty were evaluated using the 68Ge/68Ga source. We adopted the criteria of the Guide for the expression of uncertainty in measurement (GUM) to evaluate DC performance. Although the manufacturer's recommended 18F calibration number for the CRC-25PET is 480, we found that the optimal number was 482. Over a period of one year, the sensitivity of the DC varied <0.1%, and the expanded uncertainty of DC measurements was 2.2%. Measurements of the certified activity of a traceable national standard were corrected, and the uncertainty of measurements as well as the accuracy of a DC were determined. Calibration numbers for DC should be regularly determined using 68Ge/68Ga calibration sources at each location to ensure the most accurate results. (author)