Systematic Assessment of the Adsorption of ^99mTc-Radiopharmaceuticals onto Plastic Syringes

Abstract

The phenomenon of adsorption of several ^99mTc-radiopharmaceuticals onto disposable syringes is common knowledge and can reach a level of up to 50%, with the result being inadequate dosing. The resulting underdosing has a substantial influence on the quality of imaging, especially in pediatric patients. Therefore, we aimed to establish a standardized in vitro assessment to investigate the adsorption of several ^99mTc-radiopharmaceuticals on various brands of syringes. Methods: The ^99mTc-radiopharmaceuticals were prepared according to manufacturer instructions. For the assessment, the disposable syringes (n = 3) were filled to one third of capacity with the ^99mTc preparation and incubated for 30 min at room temperature. The syringes were emptied into evacuated vials, and the radioactivity of the syringes was measured before and after they were emptied. Furthermore, the dilution effect of ^99mTc preparations was studied. We used 2 different brands of syringes and systematically examined ^99mTc-pertechnetate, ^99mTc-butedronate, ^99mTc-oxidronate, ^99mTc-medronate, ^99mTc-tetrofosmin, ^99mTc-sestamibi, ^99mTc(V)-dimercaptosuccinic acid, and ^99mTc-succimer. Additionally, ^99mTc-succimer was retested with 5 brands of syringes. Results: ^99mTc-pertechnetate, ^99mTc-phosphonates, and ^99mTc(V)-dimercaptosuccinic acid showed no significant adsorption. The measured radioactive retention of 2%–5% was equivalent to the determined dead volume. Using ^99mTc-tetrofosmin, we found a slight but significant adsorption of 4%–7%. The ^99mTc-sestamibi preparation showed a nonsignificant retention of 3%–5%. However, when the ^99mTc-sestamibi was diluted 1:10 with saline, the adsorption rate increased to 9%–13%. ^99mTc-succimer displayed different adsorption levels depending on the brand of syringe and the preparation technique. The adsorption of ^99mTc-succimer, prepared from kits according to the instructions, did not exceed 15%. The 1:10 saline dilution of a ^99mTc-succimer kit preparation, as well as an in-house preparation, demonstrated a radioactive syringe adsorption rate of more than 30%. Conclusion: The results revealed the significance of syringe adsorption of radiopharmaceuticals in the prevention of underdosing. Therefore, a quality assurance assessment is recommended before the introduction of new brands of plastic syringes or routine application of diluted or in-house radiopharmaceuticals.