Fifty Shades of Scandium: Comparative Study of PET Capabilities Using Sc-43 and Sc-44 with Respect to Conventional Clinical Radionuclides.

Thiago V M Lima,Silvano Gnesin,Cristina Müller,Maria Del Sol Pérez,Justus E Roos,Nicholas P Van Der Meulen,Klaus Strobel

doi:10.3390/diagnostics11101826

Abstract

Scandium-44 has been proposed as a valuable radionuclide for Positron Emission Tomography (PET). Recently, scandium-43 was introduced as a more favorable option, as it does not emit high-energy γ-radiation; however, its currently employed production method results in a mixture of scandium-43 and scandium-44. The interest in new radionuclides for diagnostic nuclear medicine critically depends on the option for image-based quantification. We aimed to evaluate and compare the quantitative capabilities of scandium-43/scandium-44 in a commercial PET/CT device with respect to more conventional clinical radionuclides (fluorine-18 and gallium-68). With this purpose, we characterized and compared quantitative PET data from a mixture of scandium-43/scandium-44 (~68% scandium-43), scandium-44, fluorine-18 and gallium-68, respectively. A NEMA image-quality phantom was filled with the different radionuclides using clinical-relevant lesion-to-background activity concentration ratios; images were acquired in a Siemens Biograph Vision PET/CT. Quantitative accuracy with scandium-43/scandium-44 in the phantom’s background was within 9%, which is in agreement with fluorine-18-based PET standards. Coefficient of variance (COV) was 6.32% and signal recovery in the lesions provided RCmax (recovery coefficient) values of 0.66, 0.90, 1.03, 1.04, 1.12 and 1.11 for lesions of 10-, 13-, 17-, 22-, 28- and 37-mm diameter, respectively. These results are in agreement with EARL reference values for fluorine-18 PET. The results in this work showed that accurate quantitative scandium-43/44 PET/CT is achievable in commercial devices. This may promote the future introduction of scandium-43/44-labelled radiopharmaceuticals into clinical use.

Highlights

Phantom (Pro-Project) filled with the radionuclide in question was aca NEMA IQ phantom (Pro-Project) filled with the radionuclide in question was quired on our recently installed Biograph Vision (Siemens Healthineers, Erlangen, Geracquired on our recently installed Biograph Vision (Siemens Healthineers, Erlangen, many), with a step-and-shot acquisition covering the whole extend of the phantom in one Germany), with a step-and-shot acquisition covering the whole extend of the phantom in bed position
Scandium radioisotopes benefit from longer half-lives than conventionally used Positron Emission Tomography (PET) nuclides such as gallium-68 and fluorine-18, which may benefit from clinical evaluation where a scan start can occur at later time points when background activity is already cleared
Scandium may be used for prospective dosimetry prior to therapy with 177 Lu or 90 Y-labeled counterparts

Summary

Introduction

We aimed to evaluate and compare the quantitative capabilities of scandium-43/scandium-44 in a commercial PET/CT device with respect to more conventional clinical radionuclides (fluorine-18 and gallium-68). [18 F]fluoro-deoxy-glucose ([18 F]FDG) is still predominant in PET imaging, but there is large interest in the development of further radionuclides to benefit from more favorable decay characteristics to match specific applications. In this regard, the availability, transport, dosimetry, and safety are critical aspects to be addressed [1,2,3,4,5]

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