PERFORMANCE EVALUATION AND CROSS-CALIBRATION OF CAPINTEC® CRC 15R AND COMECER DOSE CALIBRATORS

ABSTRACT

Dose calibrators are used for accurate measurement of radionuclide activity which is required to achieve the desired efficacy for the best clinical outcome. Observations from assayed activity with Capintec and Comecer dose calibrators at the nuclear medicine department of the Korle-Bu Teaching Hospital have indicated that the two systems report significantly different (>10%) readings for the same activity source. Also unusually high background readings (>20% of the mean) have been noted at the 137Cs and 99mTc radionuclide settings for Capintec. The study therefore investigated the reasons for these observations so as to cross-calibrate the two systems to enable accurate measurements of radionuclide sources. Constancy check with 137Cs standard radionuclide source found Comecer and Capintec systems to have standard deviations of 1.2% and 0.74% respectively.The study also revealed deviations within ±5% tolerance for relative response to 137Cs standards at clinically significat radionuclide settings for both systems. The results for accuracy in the measurement of 137Cs standards for Comecer and Capintec systems were found to be 185.1 μCi ±1.4% and 193.7 μCi ±3.1% respectivey. Using constant activity method, both vial and syringe geometry testing yielded uncertainties within ±2% tolerance for both systems. Linearity response for both systems yielded deviations within ±5% tolerance.

However, the study revealed underestimation with Comecer and overestimation with Capintec for 99mTc assays below 1 mCi by 13-16% and 11-31% respectively. The study also found evidence of residual contamination for Capintec systems within tolerance levels. A calibration curve was developed to determine theoretical activities of 99mTc on Capintec with Comecer as the reference dose calibrator and the results gave assay accuracy within ±5% tolerance levels. Investigation of the influence of

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dial values supplied by Capintec on the measured activity readings on their system found drifts in the gain settings to be the reason for higher measurement readings as compared to Comecer system. However, new dial values were theoretically determined and the gain setting was adjusted to give assay accuracy within ±5% tolerance for 99mTc and 137Cs sources. Performance evaluation and cross-calibration have been done on Capintec and Comecer dose calibrators. The study revealed variations in the performance of both systems within tolerance levels recommended by standard protocols using appropriate settings and procedures (AAPM Report 181, 2012, IAEA TRS 454, 2006, ANSI N42.13 2004, and IAEA-TECDOC-602, 1991).