SU‐E‐T‐702: SIR‐Spheres Dose Vial Activity Assay Cross‐Calibration with An Outside Radiopharmacy

Abstract

Purpose:To perform a dose calibrator (DC) cross‐calibration for assaying SIR‐Spheres patient doses after out‐sourcing dose dispensing to an outside radiopharmacy.Methods:The setting for our DC (CRC‐15R, Capintec) required for our assay to match that of the outside radiopharmacy (accounting for decay) was determined independently for 20 dispensed doses (v‐vial in acrylic shield). The mean of the twenty settings, plus and minus one and two standard deviations, as well as, minimum and maximum, were computed. For the next 20 doses, the activity was measured using the computed DC settings. From those measurements, a least squares fit of % error with respect to the outside radiopharmacy's specified activity versus DC setting was generated to indicate an optimum single dose calibrator setting for measuring future doses. An ionization chamber survey meter (451B, Fluke Biomedical) was used in a fixed geometry to measure the exposure rate of each of the first 20 dispensed doses, and generate a linear correlation of meter reading versus radiopharmacy‐specified activity, to provide an independent method of verifying that activity.Results:Survey meter measurements demonstrated reliability of the radiopharmacy's specified activities, with R2 equal to 0.99 and a conversion factor (slope) of 0.0584 [mR/hr]/mCi. The range of DC settings yielded activity readout range of ±5.25%. The least squares fit of % error relative to the radiopharmacy's specified activity versus computed DC setting had an R2 value of 0.999 and the fit passed through 0% error very near 63×10. Each data point in the fit was the mean of 20 measurements at each setting.Conclusion:An outside radiopharmacy's assay of SIR‐Spheres doses was validated, and our data suggest that a single DC setting may be used for an in‐house activity assay within approximately 5% of that from the outside radiopharmacy.