First Phantom-Based Quantitative Assessment of Scandium-44 Using a Commercial PET Device

Scandium (Sc) is a promising candidate for theranostic applications due to the existence of radioisotopes suitable for both imaging and therapy. A “proof-of-concept” study regarding first-in-human use of 44Sc for imaging metastatic neuroendocrine tumors was reported recently, however, quantitative assessment of 44Sc-based PET images was not performed. The aim of this study was to evaluate quantitative capabilities of 44Sc-PET using a commercial PET scanner. The NEMA/IEC body phantom with 44Sc was acquired according to the local protocol used for whole-body oncological [18F]FDG PET examinations. Additionally, we characterized the signal recovery (recovery coefficient—RC) according to the iteration number. For all reconstructions, pertinent image corrections (normalization, dead time, activity decay, random coincidence, and attenuation) were applied. Presently, 44Sc scatter corrections are not optimized and could, thus, result in quantitative bias. To investigate the best option, the data were reconstructed using different available scatter corrections (relative -RelSC- and absolute -AbsSC-) and an additional prompt-gamma correction (PGC). System cross-calibration with the local dose calibrator (BGcal) and image noise, expressed by the coefficient of variation (COV), were evaluated in the homogeneous background region (5 kBq/mL) of the phantom. Maximum (RCmax) and 50% threshold recovery coefficients, corrected for background (RCA50), were measured for all spherical inserts (25 kBq/mL) of the phantom. Acceptable COV (