Pharmacokinetics of 99mTc-MAA- and 99mTc-HSA-Microspheres Used in Preradioembolization Dosimetry: Influence on the Liver-Lung Shunt

Perfusion scintigraphy using Tc-99m-labeled albumin aggregates is mandatory before hepatic radioembolization with Y-90-microspheres. As part of a prospective trial, the intrahepatic and intrapulmonary stability of 2 albumin compounds, Tc-99m-MAA (macroaggregateci serum albumin [MAN] and Tc-99m-HSA (human serum albumin [HSA]), was assessed. Methods: In 24 patients with metastatic colorectal cancer, biodistribution (liver, lung) and liver lung shunt (LLS) of both tracers (12 patients each) were assessed by sequential planar scintigraphy (1, 5, and 24 h after injection). Results: Liver uptake of both albumin compounds decreased differently. Although initial LLSs at 1 h after injection were similar in both groups, MAA-LLS increased significantly from 1 (3.9%) to 5 h (7.7%) and 24 h (9.9%) after injection, respectively. HSA-LLS did not change significantly (1 to 5 h), indicating a steady state of pulmonary and intrahepatic degradation. Conclusion: Compared with Tc-99m-MAA-microspheres, Tc-99m-HSA-microspheres are likely more resistant to degradation over time, allowing a reliable LLS determination even at later time points.