A Gelatin Liver Phantom of Suspended 90Y Resin Microspheres to Simulate the Physiologic Microsphere Biodistribution of a Postradioembolization Liver

Abstract

For phantom studies involving 90 Y PET/CT, homogeneous solutions of 90 Y, for example, 90 Y citrate, are commonly used. However, the microsphere biodistribution of a postradioembolization liver is never homogeneous; therefore, such phantoms are physiologically unrealistic for simulating clinical scenarios. The aim of this work was to develop a safe and practical phantom capable of simulating the heterogeneous microsphere biodistribution of a postradioembolization liver. Methods: Gelatin (5%) was used to suspend 90 Y resin microspheres, poured into plastic containers to simulate a liver with 2 tumors. Microspheres were added while the gelatin was maintained in a liquid state on a hot plate and continuously stirred with magnetic stir bars. The liquid microsphere mixture was then rapidly cooled in an ice bath while being stirred, resulting in a heterogeneous suspension of microspheres. The completed phantom was serially scanned by 90 Y PET/CT over 2 wk. Results: All scans demonstrated a heterogeneous microsphere distribution throughout the liver and tumor inserts. Serendipitously, magnetic stir bars left inside the phantom produced CT artifacts similar to those caused by embolization coils, whereas pockets of air trapped within the gelatin during its preparation mimicked gas within hollow viscus. The microspheres and tumor inserts remained fixed and suspended within the gelatin, with no evidence of breakdown or leakage. Conclusion: A gelatin phantom realistically simulating the physiologic microsphere biodistribution of a postradioembolization liver is feasible to construct in a radiopharmacy. For 90 Y PET/CT phantom studies, homogeneous solutions of 90 Y, for example, 90 Y-citrate, are commonly used. However, the microsphere biodistribution of a postradioembolization liver is never homogeneous (9); therefore, such phantoms are physiologically unrealistic for simulating clinical scenarios. The aim of this work was to develop a safe and practical phantom capable of simulating the heterogeneous microsphere biodistribution of a postradioembolization liver throughout both tumor and nontumor liver compartments with a physiologically realistic tumorto-normal liver ratio. MATERIALS AND METHODS Phantom ConstructionInstitutional Review Board approval was not required for the conduct and publication of this phantom study, which did not involve any human subjects. The phantom design was inspired by a gel-based phantom used by Goedicke et al. to overcome the problem of microsphere sedimentation (7). For this phantom, the medium used to suspend the microspheres was gelatin. A 5%-byweight solution of gelatin was prepared by slowly dissolving 75 g of gelatin into 1,500 mL of distilled sterile water (for injection/ irrigation). The solution was kept at 45°C on a hot plate and magnetically stirred at 300 rpm to ensure that the gelatin would not set. The liver phantom was a 1,330-mL rectangular homeware container made of clear, rigid plastic. The 2 tumor inserts were round containers made of similar plastic material, measuring 27 an...

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