Optimal dispensing and configuration of ^99mTc-MAA unit doses.

Objectives: ^99mTc-macroaggregated albumin (MAA) is a liquid suspension of technetium-99m labeled to human aggregated particles. These radiolabeled MAA particles will settle when dispensed in syringes secondary to gravity. The purpose of this study was to determine the best dispensing configuration of these unit doses to optimize the net final dose activity administered to the patient.

Methods: Forty ^99mTc-MAA doses were dispensed in 3cc syringes and calibrated as 3 mCi, six hours post dispensing. The final volume of the MAA unit doses were standardized to 1.0 ml using sterile 0.9% sodium chloride. Six hours was chosen as the amount of time to simulate delivery and distribution to an off-site facility taking into consideration transportation and actual patient schedules. Of the 40 doses, 20 doses were drawn and dispensed with regular needles and the other 20 were capped with luer locks. After six hours, the doses were assayed, and the time and activity was recorded. Ten doses from each configuration were inverted and tapped twice (agitation) prior to injecting into an evacuated vial to simulate a typical patient injection. The other ten from each configuration were injected into the vial without any inversion and agitation. The residual of each syringe, needle and luer lock were assayed separately and recorded.

Results: Data from the 40 ^99mTc-MAA unit doses were analyzed with the results summarized in Table 1.

Conclusions: The results showed that there was a greater than 60% reduction in residual activity when the syringes were inverted and agitated prior to administration regardless of the configuration of the syringes. The dispensing configuration with the lowest average residual activity and variance was that which included a needle with inversion and agitation.

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