Towards standardization of absolute SPECT/CT quantification: a multi-center and multi-vendor phantom study

Abstract

Absolute quantification of radiotracer distribution using SPECT/CT imaging is of great importance for dosimetry aimed at personalized radionuclide precision treatment. However, its accuracy depends on many factors. Using phantom measurements, this multi-vendor and multi-center study evaluates the quantitative accuracy and inter-system variability of various SPECT/CT systems as well as the effect of patient size, processing software and reconstruction algorithms on recovery coefficients (RC). Methods: Five SPECT/CT systems were included: Discovery™ NM/CT 670 Pro (GE Healthcare), Precedence™ 6 (Philips Healthcare), Symbia Intevo™, and Symbia™ T16 (twice) (Siemens Healthineers). Three phantoms were used based on the NEMA IEC body phantom without lung insert simulating body mass indexes (BMI) of 25, 28, and 47 kg/m 2. Six spheres (0.5-26.5 mL) and background were filled with 0.1 and 0.01 MBq/mL 99m Tc-pertechnetate, respectively. Volumes of interest (VOI) of spheres were obtained by a region growing technique using a 50% threshold of the maximum voxel value corrected for background activity. RC, defined as imaged activity concentration divided by actual activity concentration, were determined for maximum (RC max) and mean voxel value (RC mean) in the VOI for each sphere diameter. Inter-system variability was expressed as median absolute deviation (MAD) of RC. Acquisition settings were standardized. Images were reconstructed using vendor-specific 3D iterative reconstruction algorithms with institute-specific settings used in clinical practice and processed using a standardized, in-house developed processing tool based on the SimpleITK framework. Additionally, all data were reconstructed with a vendor-neutral reconstruction algorithm (Hybrid Recon™; Hermes Medical Solutions). Results: RC decreased with decreasing sphere diameter for each system. Intersystem variability (MAD) was 16 and 17% for RC mean and RC max , respectively. Standardized reconstruction decreased this variability to 4 and 5%. High BMI hampers quantification of small lesions (< 10 ml). Conclusion: Absolute SPECT quantification in a multi-center and multi-vendor setting is feasible, especially when reconstruction protocols are standardized, paving the way for a standard for absolute quantitative SPECT.

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

“…This is key for, e.g., multi-center research trials involving absolute SPECT quantification, especially those aimed towards dosimetry. Our previous study compared quantification for SPECT/CT systems from different vendors at different imaging centers for technetium-99 m and showed that standardizing reconstruction decreased inter-system variability [25]. The aim of this study is to extend these findings to 177 Lu.…”

Recommendations for Multicentre Clinical Trials Involving Dosimetry for Molecular Radiotherapy

“…In a later study, they evaluated the accuracy and reproducibility of activity quantification of planar and SPECT imaging in a multicentre setting with an IAEA phantom study for 133 Ba, which was used as a surrogate for 131 I [19]. Peters et al [20] carried out phantom measurements as part of a multivendor and multicentre study to assess the quantitative accuracy and inter-system variability of SPECT/CT systems. Both Zimmerman et al [18,19] and Peters et al [20] found that absolute SPECT quantification in a multicentre, multinational setting is feasible, but that standardisation of image acquisition, reconstruction parameters and processing is key.…”

SPECT/CT: Standing on the Shoulders of Giants, It Is Time to Reach for the Sky!

“…This was compounded by the rapid take-off of PET/CT, which had the advantage of being intrinsically quantitative and, in addition, was less prone to variation between vendors-or so it was perceived. It was a wake-up call that every innovation needs careful validation and standardization before clinical implementation, a lesson that reverberates even today (11).…”

“…Multiple collaborative groups have started ambitious projects aimed at standardizing quantitative SPECT/CT and creating protocols to determine the accuracy and uncertainties of specific dosimetry platforms (11,44). However, these have been hampered by a tendency to sacrifice user control of application settings and transparency in closed-source workstation solutions using proprietary algorithms in favor of easy-to-use interfaces.…”