Variability in lutetium-177 SPECT quantification between different state-of-the-art SPECT/CT systems

Steffie M B Peters; Sebastiaan L Meyer Viol; Niels R van der Werf; Nick de Jong; Floris H P van Velden; Antoi Meeuwis; Mark W Konijnenberg; Martin Gotthardt; Hugo W A M de Jong; Marcel Segbers

doi:10.1186/s40658-020-0278-3

Variability in lutetium-177 SPECT quantification between different state-of-the-art SPECT/CT systems

EJNMMI Phys. 2020 Feb 11;7(1):9. doi: 10.1186/s40658-020-0278-3.

Affiliations

¹ Department of Radiology and Nuclear Medicine, Department of Radiology and Nuclear Medicine, Radboud University Medical Center, P.O. Box 9101, 6500, HB, Nijmegen, The Netherlands. [email protected].
² Department of Radiology and Nuclear Medicine, University Medical Center Utrecht, Utrecht, The Netherlands.
³ Department of Radiology and Nuclear Medicine, Erasmus MC, Rotterdam, The Netherlands.
⁴ Department of Radiology, Section of Medical Technology, Leiden University Medical Center, Leiden, The Netherlands.
⁵ Department of Radiology and Nuclear Medicine, Department of Radiology and Nuclear Medicine, Radboud University Medical Center, P.O. Box 9101, 6500, HB, Nijmegen, The Netherlands.

^# Contributed equally.

Abstract

Background: Quantitative SPECT imaging in targeted radionuclide therapy with lutetium-177 holds great potential for individualized treatment based on dose assessment. The establishment of dose-effect relations requires a standardized method for SPECT quantification. The purpose of this multi-center study is to evaluate quantitative accuracy and inter-system variations of different SPECT/CT systems with corresponding commercially available quantitative reconstruction algorithms. This is an important step towards a vendor-independent standard for quantitative lutetium-177 SPECT.

Methods: Four state-of-the-art SPECT/CT systems were included: Discovery™ NM/CT 670Pro (GE Healthcare), Symbia Intevo™, and two Symbia™ T16 (Siemens Healthineers). Quantitative accuracy and inter-system variations were evaluated by repeatedly scanning a cylindrical phantom with 6 spherical inserts (0.5 - 113 ml). A sphere-to-background activity concentration ratio of 10:1 was used. Acquisition settings were standardized: medium energy collimator, body contour trajectory, photon energy window of 208 keV (± 10%), adjacent 20% lower scatter window, 2 × 64 projections, 128 × 128 matrix size, and 40 s projection time. Reconstructions were performed using GE Evolution with Q.Metrix™, Siemens xSPECT Quant™, Siemens Broad Quantification™ or Siemens Flash3D™ algorithms using vendor recommended settings. In addition, projection data were reconstructed using Hermes SUV SPECT™ with standardized reconstruction settings to obtain a vendor-neutral quantitative reconstruction for all systems. Volumes of interest (VOI) for the spheres were obtained by applying a 50% threshold of the sphere maximum voxel value corrected for background activity. For each sphere, the mean and maximum recovery coefficient (RC_mean and RC_max) of three repeated measurements was calculated, defined as the imaged activity concentration divided by the actual activity concentration. Inter-system variations were defined as the range of RC over all systems.

Results: RC decreased with decreasing sphere volume. Inter-system variations with vendor-specific reconstructions were between 0.06 and 0.41 for RC_mean depending on sphere size (maximum 118% quantification difference), and improved to 0.02-0.19 with vendor-neutral reconstructions (maximum 38% quantification difference).

Conclusion: This study shows that eliminating sources of possible variation drastically reduces inter-system variation in quantification. This means that absolute SPECT quantification for ¹⁷⁷Lu is feasible in a multi-center and multi-vendor setting; however, close agreement between vendors and sites is key for multi-center dosimetry and quantitative biomarker studies.