Comparison of adsorption of In-111 radiopharmaceuticals on acrylic and polypropylene

Introduction: Previous study confirmed that ¹¹¹In radiopharmaceuticals adsorb on the walls of acrylic phantoms. Adsorption of radiopharmaceuticals on the walls of acrylic phantoms can interfere with the analysis of phantom experiments, and the adsorption rate of ¹¹¹In radiopharmaceuticals on each material must be calculated to determine which material phantom can be used to prevent adsorption when phantom experiments are performed. In this study, we evaluated the adsorption of ¹¹¹In radiopharmaceuticals on acrylic phantoms and polypropylene syringes, and examined the change in adsorption depending on the material.

Methods: Three radiopharmaceuticals were used: ¹¹¹In-pentetreotide, ¹¹¹In-DTPA, and ¹¹¹InCl₃. Acrylic phantoms were 80 mL acrylic containers, and syringes were polypropylene without silicone coating. First, ¹¹¹In radiopharmaceuticals were sealed in the acrylic phantom, and counts were collected by planar imaging of the phantom. Twelve days later, the radiopharmaceuticals were removed from the phantom and counts were collected again. The adsorption rate was calculated as the counts of the phantom with the radiopharmaceuticals removed relative to those with the radiopharmaceuticals contained. Next, 5 mL of radiopharmaceuticals was withdrawn with a syringe, and the radioactivity was measured with a dose calibrator. Five minutes later, the radiopharmaceuticals were removed, rinsed with water, and the radioactivity was measured again. The radioactivity was calculated as the adsorption ratio of the radioactivity when the radiopharmaceuticals were removed to that when the radiopharmaceuticals were added.

Results: The adsorption rates of the three radiopharmaceuticals on the acrylic phantom were 29.2% for ¹¹¹InCl₃, 0.54% for ¹¹¹In-pentetreotide, and 0.15% for ¹¹¹In-DTPA. The adsorption rates on polypropylene syringes were 8.3% for ¹¹¹InCl₃, 7.0% for ¹¹¹In-pentetreotide, and 5.7% for ¹¹¹In-DTPA.

Conclusions: For ¹¹¹InCl₃, the adsorption rate was higher for acrylic than for polypropylene. On the other hand, for ¹¹¹In-pentetreotide and ¹¹¹In-DTPA, the adsorption rate was higher for polypropylene than for acrylic.