Radioembolization with Y glass microspheres for hepatocellular carcinoma: significance of pretreatment C-acetate and F-FDG PET/CT and posttreatment Y PET/CT in individualized dose prescription.

Purpose: The aim of this study was to establish an algorithm for the prescription of Y glass microsphere radioembolization (Y-GMRE) of HCC in individual patients based on the relationship between tumour dose (TD) and response validated by Y PET/CT dosimetry and dual-tracer PET/CT metabolic parameters.

Methods: The study group comprised 62 HCC patients prospectively recruited for Y-GMRE who underwent pretreatment dual-tracer (C-acetate and F-FDG) PET/CT as surrogate markers of HCC cellular differentiation. Pretreatment tumour-to-nontumour ratio on Tc-MAA SPECT/CT (T/NT) was correlated with posttreatment Y PET/CT T/NT after quantification validation. The TD-response relationship for HCC of different tracer groups was assessed on follow-up PET/CT 2 months after treatment.

Results: Y PET/CT was accurate in the measurement of recovery of injected Y activity (81.9-99.9%, median 94.8%). Pretreatment SPECT/CT T/NT was strongly correlated with posttreatment Y PET/CT T/NT (5.6 ± 3.2 versus 5.9 ± 3.5, T/NT 1.01 × T/NT + 0.161, r = 0.918, P < 0.05). The response rates were 72.4% (21/29), 70.6% (12/17) and 25% (4/16) for well, moderately and poorly differentiated HCC, respectively. The cut-off TD for a good response was significantly different between poorly differentiated and well/moderately differentiated HCC (262 Gy versus 152/174 Gy) with 89.2% sensitivity and 88% specificity. At a limiting tolerated liver dose of 70 Gy, the T/NT thresholds for predicting a good response in poorly differentiated and well/moderately differentiated HCC were 3.5 and 2.0/2.3. Disregarding HCC cellular differentiation, the cut-off TD became 170 Gy, with lower sensitivity (70.3%) and specificity (76%).

Conclusion: Y PET/CT can provide accurate dosimetry for Y-GMRE. Pretreatment T/NT predicts posttreatment T/NT. The TD thresholds for a good response are tracer-dependent, with a strong correlation between HCC radiosensitivity and cellular differentiation and other PET-based parameters. These cytokinetic factors improve treatment efficacy while minimizing organ damage for the prescription of personalized Y-GMRE.