Yttrium-90 imaging with Digital Photon Counting PET/CT: An intra-individual comparison with conventional photomultiplier tube-based PET/CT following radioembolization

Objectives: There remains an unmet clinical need for improved imaging assessment of intrahepatic Yttrium-90 (⁹⁰Y) microsphere biodistribution following radioembolization. At present, post-radioembolization imaging assessment is commonly performed using bremsstrahlung SPECT/CT but this approach is limited by poor image quality and lack of quantitative accuracy due to scatter radiation. Conventional photomultiplier tube-based PET (cPET) imaging of ⁹⁰Y internal pair production enables better image quality but often at the expense of longer image acquisition times. It has been demonstrated that ⁹⁰Y imaging with next-generation digital photon counting PET/CT (dPET/CT) is clinically feasible in post-radioembolization patients with imaging times comparable to bremsstrahlung SPECT/CT. The objective of this study is to qualitatively and quantitatively assess intrahepatic ⁹⁰Y microsphere distribution following radioembolization using dPET/CT and compare to cPET/CT. Methods: In a Phase I intra-individual comparison trial, pre-radioembolization ^99mTc MAA SPECT/CT and post-therapy bremsstrahlung ⁹⁰Y SPECT/CT imaging of the liver was performed (Symbia, Siemens) in 25 patients who were routinely treated with ⁹⁰Y glass microspheres for hepatic malignancies/metastases. Investigational ⁹⁰Y dPET/CT (Vereos, Philips) and cPET/CT (Gemini, Philips) imaging was performed with Time-of-Flight using shorter total imaging acquisition times (21 min for PET/CT vs 22 min for SPECT/CT) in each patient up to 48 hrs following radioembolization. Image quality of dPET/CT and cPET/CT was evaluated by matched pair comparison by a reader panel. Volumetric isocontouring of intrahepatic ⁹⁰Y radioactivity was also performed and compared using an IntelliSpace Portal workstation (Philips). Results: All 25 patients had evaluable post-radioembolization dPET/CT and cPET/CT images for qualitative assessment of intrahepatic ⁹⁰Y radioactivity. Despite the shorter image acquisition time, both dPET and cPET images demonstrate better image quality and improved ⁹⁰Y-to-background contrast when compared with standard bremsstrahlung SPECT. Qualitatively, dPET/CT enabled more precise localization of the ⁹⁰Y microsphere distribution within the liver when compared with cPET/CT. Similarly, volumetric isocontouring of the intrahepatic ⁹⁰Y activity demonstrated consistently and significantly smaller ⁹⁰Y-treated liver volumes with dPET than with cPET (average ⁹⁰Y-treated liver volume was 1064 +/- 570 mL for dPET and 1372 +/- 634 mL for cPET, P < 0.05). Conclusion: These results demonstrate that next-generation digital photon counting PET detector technology enables faster ⁹⁰Y imaging with improved image quality and ⁹⁰Y-to-background contrast than bremsstrahlung SPECT/CT approaches. In addition, dPET/CT more precisely localizes ⁹⁰Y microsphere activity within the liver than cPET/CT which is consistently demonstrated with smaller ⁹⁰Y-treated liver volumes on dPET/CT. In the future, dPET/CT may improve qualitative evaluation of ⁹⁰Y microsphere biodistribution for the assessment of concordance/discordance with pre-therapy imaging as well as foster new quantitative methodologies for ⁹⁰Y-dosimetry. Research Support: Ohio Third Frontier (TECH 09-028, TECH 10-012, TECH 13-060) and Philips Healthcare provided the investigational pre-commercial release dPET/CT.

• Download figure
• Open in new tab
• Download powerpoint