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).MethodsFive 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/m2. Six spheres (0.5–26.5 mL) and background were filled with 0.1 and 0.01 MBq/mL 99mTc-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 (RCmax) and mean voxel value (RCmean) 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).ResultsRC decreased with decreasing sphere diameter for each system. Inter-system variability (MAD) was 16 and 17% for RCmean and RCmax, respectively. Standardized reconstruction decreased this variability to 4 and 5%. High BMI hampers quantification of small lesions (< 10 ml).ConclusionAbsolute 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.
Highlights
Accurate absolute quantification of radiotracer distribution is essential for dosimetry aimed at personalized radionuclide therapy and may improve prediction of therapy response, prevention of toxicity effects, and treatment follow-up [1, 2]
An earlier study by Seret et al [32] compared the quantitative capabilities of four single-photon emission computed tomography (SPECT)/computed tomography (CT) cameras, our study included the current state-of-the-art quantitative SPECT/CT systems that enable absolute quantification that were not available at that time
This study shows that absolute SPECT quantification is feasible in a multi-center and multi-vendor setting
Summary
Accurate absolute quantification of radiotracer distribution is essential for dosimetry aimed at personalized radionuclide therapy and may improve prediction of therapy response, prevention of toxicity effects, and treatment follow-up [1, 2]. Both positron emission tomography (PET) and single-photon emission computed tomography (SPECT) hold the promise for absolute radioactivity quantification. Recent developments in corrections for photon attenuation and scatter, collimator modeling and 3D reconstruction, e.g., by including resolution recovery and noise regulation, have improved reconstruction techniques, thereby enabling absolute SPECT quantification [5]. Nowadays, combined SPECT/CT systems have become standard clinical practice
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