[Effects of Different Containers on Radioactivity Measurements using a Dose Calibrator with Special Reference to In and I].

Low-energy characteristic x-rays emitted by In and I sources are easily absorbed by the containers of the sources, affecting radioactivity measurements using a dose calibrator. We examined the effects of different containers on the estimated activities. The radioactivities of In, I, Tl, and Tc were measured in containers frequently employed in clinical practice in Japan. The In measurements were performed in the vials A and B of the In-pentetreotide preparation kit and in the plastic syringe. The activities of I-metaiodobenzylguanidine and Tl chloride were measured in the prefilled glass syringes and plastic syringes. The milking vial, vial A, vial B, and plastic syringe were used to assay Tc. For In and I, measurements were performed with and without a copper filter. The filter was inserted into the well of the dose calibrator to absorb low-energy x-rays. The relative estimate was defined as the ratio of the activity estimated with the dose calibrator to the standard activity. The estimated activities varied greatly depending on the container when In and I sources were assayed without the copper filter. The relative estimates of In were 0.908, 1.072, and 1.373 in the vial A, vial B, and plastic syringe, respectively. The relative estimates of I were 1.052 and 1.352 in the glass syringe and plastic syringe, respectively. Use of the copper filter eliminated the container-dependence in In and I measurements. Container-dependence was demonstrated in neither Tl nor Tc measurements. The activities of In and I estimated with a dose calibrator differ greatly among the containers. Accurate estimation may be attained using the container-specific correction factor or using the copper filter.