Accuracy of quantitative ¹⁷⁷Lu SPECT/CT imaging: A systematic review

Accurate quantification of lutetium-177 (¹⁷⁷Lu) activity in SPECT/CT imaging is essential for a further development of ¹⁷⁷Lu-based peptide receptor radionuclide therapy (PRRT) in establishing absorbed dose-effect relationships. This review summarizes the reported accuracy of quantitative ¹⁷⁷Lu SPECT/CT imaging and highlights key sources of variability, including partial-volume effect (PVE) in small volumes. A systematic review was conducted according to PRISMA guidelines. MEDLINE, EMBASE, and Web of Science databases were searched with no language restrictions. Original studies explicitly reporting on the accuracy of ¹⁷⁷Lu activity quantifications in physical SPECT/CT measurements were included. Reported percentage error/deviation and recovery coefficient (RC) were extracted and compiled, with studies grouped by object type (geometric phantoms, anthropomorphic phantoms, and patient data). The literature search identified 630 records, of which 46 studies were included for analysis. Percentage errors of quantifications were found to constitute a large range (-102% to 285%). The recovery of ¹⁷⁷Lu activity from small volumes is inherently limited by PVE. The application of PVC has led to improvements in the accuracy and precision of quantifications on small volumes in phantom imaging. The accuracy of ¹⁷⁷Lu activity quantifications in SPECT/CT imaging remains heterogenous across literature, is subject to large variability and will be degraded by PVE when imaging small volumes. The data suggests that the implementation of standardized procedures including standardization of calibration, reconstruction, segmentation, and PVC assumptions may lead to an improved accuracy and precision of quantitative ¹⁷⁷Lu SPECT/CT imaging in clinical practice, thereby allowing the further development of ¹⁷⁷Lu-based PRRT.