Multi-centre evaluation of accuracy and reproducibility of planar and SPECT image quantification: An IAEA phantom study

Abstract

Accurate quantitation of activity provides the basis for internal dosimetry of targeted radionuclide therapies. This study investigated quantitative imaging capabilities at sites with a variety of experience and equipment and assessed levels of errors in activity quantitation in Single-Photon Emission Computed Tomography (SPECT) and planar imaging. Participants from 9 countries took part in a comparison in which planar, SPECT and SPECT with X ray computed tomography (SPECT-CT) imaging were used to quantify activities of four epoxy-filled cylinders containing 133Ba, which was chosen as a surrogate for 131I. The sources, with nominal volumes of 2, 4, 6 and 23 mL, were calibrated for 133Ba activity by the National Institute of Standards and Technology, but the activity was initially unknown to the participants. Imaging was performed in a cylindrical phantom filled with water. Two trials were carried out in which the participants first estimated the activities using their local standard protocols, and then repeated the measurements using a standardized acquisition and analysis protocol. Finally, processing of the imaging data from the second trial was repeated by a single centre using a fixed protocol. In the first trial, the activities were underestimated by about 15% with planar imaging. SPECT with Chang’s first order attenuation correction (Chang-AC) and SPECT-CT overestimated the activity by about 10%. The second trial showed moderate improvements in accuracy and variability. Planar imaging was subject to methodological errors, e.g., in the use of a transmission scan for attenuation correction. The use of Chang-AC was subject to variability from the definition of phantom contours. The project demonstrated the need for training and standardized protocols to achieve good levels of quantitative accuracy and precision in a multi-centre setting. Absolute quantification of simple objects with no background was possible with the strictest protocol to about 6% with planar imaging and SPECT (with Chang-AC) and within 2% for SPECT-CT.

The Relevance of Dosimetry in Precision Medicine

“…An overview of the most recently applied methods for SPECT/ CT quantification with therapeutically used radionuclides, different phantom geometries, volumes, camera vendors, reconstruction methods, and the related accuracies has been provided by Tran-Gia et al (24). Table 1 shows only publications with reported accuracies of less than 10% (25)(26)(27)(28)(29)(30)(31)(32).…”

“…In an international multicenter calibration and standardization trial, Zimmerman et al (25) found by using calibrated 133 Ba sources that SPECT/CT systems showed better reproducibility and better accuracy than planar imaging. The results for SPECT/CT were almost operator-independent.…”

Characterization of Noise and Resolution for Quantitative 177Lu SPECT/CT with xSPECT Quant

“…In contrast, image-domain correction techniques try to restore spilled-out counts on the basis of anatomic information or predetermined experimental findings, such as by multiplication with a spheric recovery coefficient (11,12) or more organ-specific correction factors obtained in anthropomorphic, 3dimensional (3D) printed phantoms (13)(14)(15). Although many efforts have been made to standardize quantitative SPECT/CT imaging (5,6,16,17), the lack of a widely accepted and routinely applied standardization still impedes a comparison of quantitative SPECT/ CT acquisitions across different clinical centers and different manufacturers. This, in turn, obstructs the conduction of multicentric or longitudinal studies for validating and optimizing the therapeutic use of new radiopharmaceuticals (18).…”

Dosimetrie für die Nuklearmedizinische Therapie

“…verabreichten Radiopharmazeutikums für die Dosimetrie beruht auf der quantitativen Bildgebung mittels serieller Gamma-Kamera-Scans und mindestens einem SPECT(/CT). Die Dosimetrie, die auf quantitativen 3-dimensionalen Daten basiert, ist erheblich genauer [3]. Darüber hinaus kann eine inhomogene Organakkumulation des Radionuklids nachgewiesen und ggf.…”