Comparison of Tc-99m MAA Planar Versus SPECT/CT Imaging for Lung Shunt Fraction Evaluation Prior to Y-90 Radioembolization: Are We Overestimating Lung Shunt Fraction?

Purpose To compare lung shunt fraction (LSF) prior to Y-90 radioembolization calculated using planar imaging versus SPECT/CT in patients with hepatocellular carcinoma (HCC). Methods A single institution retrospective analysis of technetium-99m macroaggregated albumin (Tc-99m MAA) LSF studies for 293 consecutive patients with HCC between 2013 and 2018 was performed. LSF using planar imaging (PLSF) was compared to retrospectively calculated LSF using SPECT/CT (SLSF) via semiautomated segmentation using MIM v.6.9. Sub-analyses of patients were performed based on PLSF range, tumor size, BCLC stage, and Child–Pugh (C–P) score. Mean LSF absolute discrepancy between sub-groups was analyzed. Comparisons were performed using paired t tests and linear regression analysis. Results Mean PLSF, 8.27%, was greater than mean SLSF, 3.27% ( p < 0.001). When categorizing patients by PLSF ranges of < 10%, 10–19.9%, and ≥ 20%, PLSF remained greater than SLSF in all subgroups ( p ’s < 0.001). Patients with PLSF ≥ 20% had a greater absolute discrepancy with SLSF (13.31%) compared to patients with PLSF < 20% (4.74%; p < 0.0001). LSF absolute discrepancy was greater for patients with a maximum liver tumor size ≥ 5.0 cm (5.59%) compared to a liver tumor size < 5.0 cm (4.40%; p = 0.0076). For all BCLC grades and C–P scores, PLSF was greater than SLSF. A greater LSF discrepancy existed for patients with a worse C–P score (C–P A: 4.78%, C–P B/C: 6.12%; p = 0.0081), but not BCLC stage (0/A/B: 4.87%, C: 4.56%; p = 0.5993). Conclusion In patients with HCC, SLSF is significantly lower compared to PLSF, with a greater discrepancy among patients with a PLSF ≥ 20%, tumor size ≥ 5 cm, and worse C–P score. Level of Evidence Level 3, Retrospective Study.