Optimizing dosimetric accuracy in radioembolization: comparative effectiveness of SPECT/CT, planar imaging, and PET/CT for lung shunt fraction assessment

Background: In radioembolization therapy for hepatic malignancies, the accurate estimation of lung shunt fraction (LSF) is crucial to minimize the risk of radiation-induced pneumonitis and fibrosis due to hepatopulmonary shunting of yttrium-90 (90Y)-microspheres. This study aimed to compare the accuracy and precision of LSF estimation using technetium-99m macroaggregated albumin single photon emission computed tomography ([99mTc]Tc-MAA SPECT) LSF, [99mTc]Tc-MAA planar LSF, and 90Y PET LSF in patients undergoing 90Y-radioembolization.

Material and methods: A retrospective study was conducted involving 15 patients diagnosed with hepatocellular carcinoma (HCC) or liver metastases and planned to undergo transarterial radioembolization with 90Y SirSpheres after multidisplinary team discussion. LSF values were calculated using [99mTc]Tc-MAA SPECT LSF, [99mTc]Tc-MAA planar LSF, and 90Y PET LSF. The accuracy of these methods was assessed through paired t-tests and correlation analysis.

Results: The paired t-test revealed a statistically significant difference between SPECT LSF and planar LSF (t-statistic = -4.81, p-value = 0.0003), indicating that planar imaging tends to overestimate LSF values. However, no significant difference was observed between [99mTc]Tc-MAA SPECT LSF and 90Y PET LSF (t-statistic = -0.98, p-value = 0.343), suggesting a high degree of agreement between these two methods. Correlation analysis showed a very strong positive correlation between [99mTc]Tc-MAA SPECT LSF and 90Y PET LSF (r = 0.999), while strong correlations were also found between SPECT LSF and planar LSF, and between planar LSF and 90Y PET LSF (r = 0.841).

Conclusions: The findings suggest that 90Y PET LSF aligns closely with [99mTc]Tc-MAA SPECT LSF, making them both reliable for LSF estimation in radioembolization therapy. In contrast, planar imaging tends to overestimate LSF, potentially leading to inaccurate dosimetric planning. Incorporating [99mTc]Tc-MAA SPECT/CT and 90Y PET/CT into routine clinical practice could enhance the accuracy of LSF estimation, thereby improving patient outcomes. Further research with larger cohorts is recommended to validate these findings.