Limitations of Rb-82 weight-adjusted dosing accuracy at low doses

Weight-adjusted dosing is important to maintain accurate quantification for dynamic cardiac three-dimensional positron emission tomography (PET). However, the manufacturer of the only Food and Drug Administration approved rubidium-82 (Rb-82) generator (CardioGen-82, Bracco Diagnostics, Inc.) recommends recalibration after each change in dose which is inefficient in a busy clinical PET lab. The objective of this study was to evaluate the accuracy of Rb-82 dosing without this recalibration.

After daily calibration to either 30 mCi (1110 MBq) or 12 mCi (444 MBq), Rb-82 doses between 6 and 45 mCi (222-1665 MBq) were eluted and measured on an external dose calibrator. This was repeated for four generators at weeks 1, 2, or 4 of the generator cycle. The measurements were compared with values reported by the infusion system.

For requested doses less than 30 mCi, the measured dose was consistently lower than the requested dose, ranging from -3.2 mCi at 25 mCi to -5.5 mCi at 10 mCi. The error exceeded 10% for doses less than or equal to 26 mCi for the 30 mCi calibration. Residual activity in the infusion system dead volume accounted for the discrepancy between requested and delivered doses for calibration to 30 mCi but not 12 mCi.

The CardioGen-82 infusion system is capable of accurate weight-adjusted doses without recalibration for Rb-82 doses as low as 26 mCi when calibrated to 30 mCi. For doses less than 26 mCi, the generator-reported residual activity within the infusion system can be used to correct the delivered dose.