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

Perfusion scintigraphy using ^99mTc-labeled albumin aggregates is mandatory before hepatic radioembolization with ⁹⁰Y-microspheres. As part of a prospective trial, the intrahepatic and intrapulmonary stability of 2 albumin compounds, ^99mTc-MAA (macroaggregated serum albumin [MAA]) and ^99mTc-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 ^99mTc-MAA-microspheres, ^99mTc-HSA-microspheres are likely more resistant to degradation over time, allowing a reliable LLS determination even at later time points.

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