Purpose: ⁴³Sc and ⁴⁴ᵍSc have desirable qualities for PET imaging: approximately 4-hour half-lives, low positron energies, and chemical similarity to therapeutic radionuclides such as ¹⁷⁷Lu. This work investigates numerous production routes available to produce both radionuclides and compares these possibilities based on yield, radionuclidic purity, and their performance on two clinical PET/CT scanners compared to conventional clinical radionuclides.
Methods: Isotopically enriched ⁴²,⁴³,⁴⁴CaO targets were fabricated and irradiated on a GE PETtrace cyclotron to produce ⁴³,⁴⁴ᵍSc through several reaction routes: ⁴²Ca(d,n)⁴³Sc, ⁴³Ca(p,n)⁴³Sc, ⁴³Ca(d,n)⁴⁴ᵍSc, ⁴⁴Ca(p,n)⁴⁴ᵍSc, and ⁴⁴Ca(p,x)⁴³,⁴⁴ᵍSc. Following irradiation, gamma spectroscopy was performed to quantify yield and radionuclidic purity. Produced radioscandium was isolated through extraction chromatography. Derenzo and sphere phantoms were filled with ¹⁸F, ⁶⁸Ga, ⁶⁴Cu, ⁴³Sc, ⁴⁴ᵍSc and a mixture of ⁴³,⁴⁴ᵍSc. The Derenzo phantom and spheres were filled with an activity concentration of approximately 20 kBq/mL and the background around 5 kBq/mL for a lesion to background ratio of 4:1. Either 60 million (sphere) or 120 million (Derenzo) coincident counts were collected on two clinical PET/CT scanners: a GE Discovery PET/CT 710 and a GE Discovery MI. Recovery coefficients, noise, contrast, and resolution were compared across radionuclides and imaging systems.
Results: ⁴⁴Ca(p,n)⁴⁴ᵍSc and ⁴²Ca(d,n)⁴³Sc resulted in the highest yields for ⁴⁴ᵍSc (717.8 ± 70.3 MBq/μAh) and ⁴³Sc (44.4 ± 5.2 MBq/μAh), respectively. Use of enriched material eliminated or reduced contaminating, long-lived radioisotopes of scandium (⁴⁶,⁴⁷,⁴⁸Sc). Image analysis demonstrated comparable image quality between radioisotopes of scandium and clinically used radionuclides while providing benefits such as longer half-lives and chemical similarity to therapeutic radionuclides such as ¹⁷⁷Lu.
Conclusion: Both ⁴³Sc and ⁴⁴ᵍSc produce high quality PET images when compared to clinically-used PET radionuclides. While ⁴³Sc has slightly favorable characteristics for imaging, these advantages must be weighed against the increase cost in target material and lower production yields compared to ⁴⁴ᵍSc.
Funding Support, Disclosures, and Conflict of Interest: Research reported in this presentation was supported by NIH Award Number: T32CA009206 and DOE Office of Science award number: DE-SC0020417. All phantoms were purchased from Phantec.
IM- PET : Cyclotron physics and radiopharmaceutical production