International Journal of Science and Technology

International Journal of Science and Technology>> Volume 7, Number 7, July 2017

International Journal of Science and Technology


Calibration and Effective Use of a Dose Calibrator

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Author B. Assan, E.K.T Addison, F. Hasford, E. Sosu
On Pages 395-400
Volume No. 2
Issue No. 6
Issue Date June, 2012
Publishing Date June, 2012
Keywords Maximum count rate, accuracy, precision, constancy, linearity measurement, dose calibrator


Abstract

Maximum count rate, accuracy, precision, constancy and linearity measurement have been undertaken on two dose calibrators at the Nuclear medicine department, Korle-Bu Teaching Hospital as part of quality control test. Both calibrators show some dependence on measurement geometry which deminishes with increasing depth in the well. It was observed that the measured activities for Co-57, Cs-137 and Tc-99m, obtained from the VDR-15R were larger than those from the reference dose calibrator, Capintec CRC-25R. It was found that, the maximum depth of sensitivity in the Capintec was 6.8 cm and 5.6 cm for Co-57 and Cs-137.VDR showed a maximum sensitivity depth of 5.2 cm for both Co-57 and Cs-137. For accuracy and precision, it was observed that, the percentage differences for the reference dose calibrator, Capintec CRC-25R was a little different from that of the VDR-15 but both calibrators were in the range of 5% of the mean measured activity. The main difference was their maximum height of sensitivities with values of 6.8 cm and 5.2 cm for Co-57 and 5.6 cm and 5.2 cm for Cs-137 for Capintec and VDR-15R respectively. From the linearity test, there were systematic departures of the data points from the fitted straight line in the upper part and lower part and such discrepancies indicated non-linearity. These discrepancies in the upper and lower part were due to impurities (Mo-99 contaminants and Tc-99 contaminants respectively) in the Tc-99m used in the test which revealed itself in apparent levelling out of the activity in the final part and beginning part of the graph. Since most of the points fitted in the straight line, it showed that, almost all the individual activities measured in the test were within the range of 10% of the values corresponding to the straight line fitted in the data points. It was observed that, the measured activities difference for both calibrators were very small which was as a result of the differences in depth of their wells. The dose calibrators can be used for dose measurements.

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