Dosimetry Based on 99mTc-Macroaggregated Albumin SPECT/CT Accurately Predicts Tumor Response and Survival in Hepatocellular Carcinoma Patients Treated with 90Y-Loaded Glass Microspheres: Preliminary Results

Radioembolization of liver cancers using Y-90-loaded microspheres is experiencing more widespread use. However, few data are available concerning the doses delivered to the tumors and the healthy liver. This retrospective study was conducted to calculate the tumor dosimetry (planned tumor dose [T-plan D]) and nontumor dosimetry in patients treated by Y-90-loaded glass microspheres and determine whether tumor dosimetry could predict response and survival. Methods: Thirty-six patients with hepatocellular carcinoma (HOC), including 16 with portal vein thrombosis (PVT), were treated with Y-99-loaded glass microspheres. The T-plan D and the dose delivered to the injected healthy liver were calculated using a quantitative analysis of the Tc-99m-macroaggregated albumin (Tc-99m-MAA) SPECT/CT exam. Responses were assessed after 3 mo, using the criteria of the European Association for the Study of the Liver. Progression-free survival (PFS) and overall survival (OS) were evaluated using Kaplan-Meier tests. Results: The response rate was 69% for the overall population and 75% for the PVT patients. The dose delivered to the tumor was the only parameter associated with response with multivariate analysis (P = 0.019). A threshold T-plan D value of 205 Gy was predictive of response, with a sensitivity of 100% and an accuracy of 91%. Quantitative Tc-99m-MAA SPECT/CT allowed us to increase the injected activity for 4 patients with large lesions. PFS was only 5.2 mo and OS 9 mo when using a T-plan D of less than 205 Gy versus 14 mo (P = 0.0003) and 18 mo (P = 0.0322), respectively, with a T-plan D of 205 Gy or more. Conclusion: Quantitative Tc-99m-MAA SPECT/CT is predictive of response, PFS, and OS. Dosimetry based on Tc-99m-MAA SPECT/CT can be used for the selection of patients and for an adaptation of treatment planning, especially in selected patients (particularly in the case of large tumors). These results also confirm the efficacy and safety of Y-90-loaded microspheres in treating HOC, even in the presence of PVT (and especially when Tc-99m-MAA uptake is seen inside the PVT).