Effects of Different Containers on Radioactivity Measurements using a Dose Calibrator with Special Reference to ¹¹¹In and ¹²³I

Abstract

Low-energy characteristic x-rays emitted by ¹¹¹In and ¹²³I 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 ¹¹¹In, ¹²³I, ²⁰¹Tl, and ^99mTc were measured in containers frequently employed in clinical practice in Japan. The ¹¹¹In measurements were performed in the vials A and B of the ¹¹¹In-pentetreotide preparation kit and in the plastic syringe. The activities of ¹²³I-metaiodobenzylguanidine and ²⁰¹Tl 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 ^99mTc. For ¹¹¹In and ¹²³I, 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 ¹¹¹In and ¹²³I sources were assayed without the copper filter. The relative estimates of ¹¹¹In were 0.908, 1.072, and 1.373 in the vial A, vial B, and plastic syringe, respectively. The relative estimates of ¹²³I were 1.052 and 1.352 in the glass syringe and plastic syringe, respectively. Use of the copper filter eliminated the container-dependence in ¹¹¹In and ¹²³I measurements. Container-dependence was demonstrated in neither ²⁰¹Tl nor ^99mTc measurements. The activities of ¹¹¹In and ¹²³I 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.