# When is patient-specific lung shunt fraction necessary in 90Y selective internal radiation therapy of liver cancer?

## TL;DR

This study proposes a new method to determine when patient-specific lung shunt fraction is necessary in liver cancer radiation therapy, potentially reducing the need for additional imaging.

## Contribution

Introduces a new metric, LSFbound, to guide when patient-specific lung shunt fraction assessment is needed in 90Y-SIRT.

## Key findings

- LSFbound depends on liver mass, lung mass, and dose thresholds, not perfused volume size.
- For most cases, the probability of needing MAA-based LSF is less than 4%.
- Pretreatment LSFbound calculation achieves 100% sensitivity and over 60% specificity in identifying necessary LSF assessments.

## Abstract

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.

To propose and evaluate a pretreatment identification method for patient-specific LSF that may influence treatment planning in 90Y-SIRT and necessitate LSF determination using MAA-based imaging.

MAA 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 is 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.

A total of 354 cases were analyzed from 297 patients (92 females and 205 males). Median (interquartile range) age at MAA-SPECT/CT was 69 (63-74). LSFbound depends only on liver mass, lung mass, Livermax, and Lungsmax, whereas PV size plays no role. Using observed LSFSPECT distributions, the median (max) probability for LSFSPECT to exceed LSFbound was ≤1% (≤4%) for hepatocellular carcinoma ≤ 8 cm and non-hepatocellular carcinoma cases without macrovascular invasion (87% of all cases). Receiver operating characteristic analysis showed that pretreatment use of LSFbound could achieve 100% sensitivity and >60% specificities at Livermax values up to 180 Gy.

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. Pretreatment calculation of LSFbound provides individualized, quantitative guidance for identifying when MAA-based, patient-specific LSF assessment is warranted.