Predictors of Lung Shunt Fraction in Y-90 Radioembolization Across Various Tumor Types

Purpose: Pre-treatment lung shunt fraction (LSF) is a critical determinant for Y-90 radioembolization safety and dosimetry. Mappings are routinely performed regardless of tumor type, characteristic, or other clinically relevant information. Prior studies have shown hepatocellular carcinoma (HCC) has higher and more variable LSF than non-HCC tumors {1-3}. We aim to identify factors predicting elevated LSF and to compare LSF distributions across tumor types.

Materials and Methods: We retrospectively reviewed 822 mapping angiograms (2012-2024) at a single center. Patients were grouped by cancer: with HCC (n = 577) and colorectal (n = 82) being the most common. LSF was categorized as Low < 10%, Intermediate 10–20%, or High > 20%. Variables tested included portal vein invasion, MELD (original, Na, and 3.0), Child–Pugh, tumor burden, tumor size, prior liver therapy, and sex. Kruskal–Wallis, Mann-Whitney U, Chi-square, or Fisher exact tests were used (p < 0.05).

Results: LSF differed significantly between cancers (p < 0.0001), with HCC showing higher and more variable shunting with a mean of 8.9. For HCC, elevated LSF was strongly associated with portal vein invasion (39.5% in high vs 9.3% in low LSF, p < .001), worse liver function (higher MELD and Child–Pugh, all p < .05), tumors >5 cm (p < .001), >3 lesions (p < .05), and prior endovascular liver therapy (p < .05).

For colorectal metastases, since there were no high LSFs, intermediate LSF was associated with larger primary tumor size > 5 cm (70% vs 35%; p < .05) and slightly higher MELD-Na (median 8.7 vs 7.5; p < .05).

For cholangiocarcinoma, neuroendocrine, breast, fibrolamellar HCC, gynecologic, and other metastatic cancers, no significant predictors of LSF were identified.

Conclusion: LSF varies significantly by cancer, with HCC demonstrating the highest and most variable values. Colorectal metastases generally show low LSF, but large tumors and worse MELD-Na significantly correlate to increased shunting. Non-HCC/colorectal tumors rarely exhibit elevated LSF or predictive factors, but this may be due to underpowered studies. These findings reinforce the need for HCC mapping due to variability; however, certain non-HCC cancers with consistently low and predictable lung shunt fractions warrant further investigation into whether mapping is universally required.