Purpose: To determine the accuracy of planar scintigraphy in estimating lung shunt fraction (LSF) in patients with high LSFs ( >15%).
Materials and Methods: A retrospective review of all Technetium-99 macroaggregated albumin (MAA) planning angiograms from 2016 to 2020 at a single institution was performed. Inclusion criteria included planar scintigrams with a measured LSF of >15% and corresponding SPECT/CT data. SPECT/CT LSF data were processed using commercial software for individual dose planning (Simplicit90Y, Boston Scientific, Marlborough, MA, USA). 3D regions of interest were manually drawn around the lungs and liver. A 1-2cm exclusion region above the right hepatic dome was used to correct for respiratory motion. Image counts from each region of interest were calculated automatically by the dose planning software. 3D-SPECT/CT LSFs were then calculated for each case. LSF differences between SPECT/CT and planar modalities were compared using Student’s t-test, ANOVA, and linear regression.
Results: 51 cases were included in the analysis. The mean planar LSF was 29.6% (+\- std 15.1%). 33/51 (65%) had Planar LSFs >20%. Mean 3D SPECT/CT LSF was 19.5% (+\- std 13.7%), significantly lower than planar measurements (p< 0.01). 12/33 (36.4%) of patients with a LSF >20% on planar scintigraphy had LSFs < 20% on SPECT/CT. Tumor location and MAA injection location had no significant association with measured LSF differences.
Conclusion: Planar scintigraphy overestimates LSF in patients with high LSFs. SPECT/CT should be used for LSF calculation in this patient population to avoid under dosing during radioembolization.
References: Allred JD, Niedbala J, Mikell JK, Owen D, Frey KA, Dewaraja YK. The value of 99mTc-MAA SPECT/CT for lung shunt estimation in 90Y radioembolization: a phantom and patient study. EJNMMI Res. 2018;8(1):50. Published 2018 Jun 15. doi:10.1186/s13550-018-0402-8
Dittmann H, Kopp D, Kupferschlaeger J, et al. A Prospective Study of Quantitative SPECT/CT for Evaluation of Lung Shunt Fraction Before SIRT of Liver Tumors. J Nucl Med. 2018;59(9):1366-1372. doi:10.2967/jnumed.117.205203