When is Patient-Specific Lung Shunt Fraction Necessary in 90Y Selective Internal Radiation Therapy of Liver Cancer?

Background Lung shunt fraction (LSF) derived from macroaggregated albumin (MAA) based nuclear medicine imaging is a standard component of yttrium-90 selective internal radiation therapy (90Y-SIRT) treatment-planning. Elimination of MAA-based LSF determination has been suggested in selected cases. Purpose To propose and evaluate a pre-treatment identification method for patient-specific LSF that may influence treatment-planning in 90Y-SIRT and necessitate LSF determination using MAA-based imaging. Methods MAA single photon emission computed tomography (SPECT)/CT based LSF (LSFSPECT) was analyzed retrospectively in glass 90Y-SIRT cases from September 2022 to June 2025 at a single center. A new metric (LSFbound) was defined as the minimum LSF value where the maximum achievable perfused volume (PV) dose becomes determined by a selected lung dose threshold (Lungsmax) instead of a designated whole-liver dose threshold (Livermax). LSFbound values computed using both clinical and simulated treatment planning parameters were quantitatively evaluated relative to LSFSPECT. A clinical workflow based on this new metric was evaluated. Results A total of 354 cases were analyzed from 297 patients (92 females and 205 males). Median (IQR) age at MAA-SPECT/CT was 69 (63–74). LSFbound depends only on liver mass, lung mass, Livermax, and Lungsmax, while PV size plays no role. Using observed LSFSPECT distributions, the median (max) probability for LSFSPECT to exceed LSFbound was ≤1% (≤4%) for HCC ≤ 8 cm and non-HCC cases without macrovascular invasion (87% of all cases). ROC analysis showed that the pre-treatment use of LSFbound could achieve 100% sensitivity and >60% specificities at Livermax values up to 180 Gy. Conclusion Patient-specific, MAA-based LSF determination may be obviated in most 90Y-SIRT cases as LSF and Lungsmax play no role in limiting the achievable PV dose. Pre-treatment calculation of LSFbound provides individualized, quantitative guidance for identifying when MAA-based, patient-specific LSF assessment is warranted.