90Y-Loaded Microsphere SIRT of HCC Patients With Portal Vein Thrombosis: High Clinical Impact of 99mTc-MAA SPECT/CT-Based Dosimetry.

Radioembolization with 90Y-loaded microspheres based on classical prescription methods is increasingly applied to hepatocellular carcinoma (HCC) patients with portal vein thrombosis (PVT). In recent years, pretherapeutic predictive dosimetry based on technetium-99m macroaggregated albumin (MAA) quantitative scintigraphy using SPECT/CT has been developed. This paper presents an overview on the MAA-based dosimetry concept, discusses important confounding factors, such segmentation methods, and specific angiographic considerations required for a simulation-based dosimetric evaluation. The concept of "dosimetric angiography" is then introduced for the first time. Main results available are reported as a threshold tumor dose, allowing a response, between 100 and 120 Gy with 90Y-loaded resin microspheres and between 205 and 257 Gy with 90Y-loaded glass microspheres. Impact of MAA-based dosimetry and MAA PVT targeting on overall survival is also reported. Due to those dosimetric advances, personalized dosimetric approaches based on MAA dosimetry are now available, with specific endpoints, for both 90Y-loaded resin or glass microsphere. The clinical impact of personalized dosimetry in PVT patients is particularly high, as a median overall survival of 20.2 months has been reported for good PVT candidate treated with glass microspheres (tumor-absorbed dose ≥205 Gy and good PVT targeting) as against only 3 months for poor candidate (tumor-absorbed dose <205 Gy or poor PVT targeting), and as a significant amount of patients where downstaged and resected (12%) in the same study.