Post-radioembolization Assessment of Intrahepatic Yttrium-90 Microsphere Biodistribution Using Next-generation Digital PET/CT and Comparison to Current Pre/post-radioembolization SPECT/CT Methodologies

Objectives There is an unmet clinical need for accurate imaging based assessment of Yttrium-90 (90Y) microsphere biodistribution in the liver following interventional radioembolization. At present, pre-radioembolization planning procedures are performed in interventional radiology using 99mTc macroaggregated albumin (MAA) and the intrahepatic biodistribution as well as extrahepatic shunting of MAA is assessed using conventional SPECT/CT approaches. Post-radioembolization assessment is typically performed using bremsstrahlung SPECT/CT but this approach is limited by poor image quality. It has been demonstrated that PET imaging of 90Y internal pair production following radioembolization yields better image quality but often at the expense of longer image acquisition times. Using next-generation digital photon counting PET detector technology (dPET) and faster total image acquisition times, our objective is to assess intrahepatic 90Y activity following radioembolization using dPET/CT and compare to pre/post-radioembolization SPECT/CT.

Methods Standard pre-radioembolization 99mTc MAA SPECT/CT and post-therapy bremsstrahlung 90Y SPECT/CT imaging of the liver was performed (Symbia) in 15 patients who were treated with 90Y glass microspheres. As part of an ongoing clinical trial, 90Y digital PET/CT (Vereos) imaging was also performed in each patient up to 50 hrs following interventional radioembolization and using faster total imaging acquisition times (21 min for dPET/CT and 22 min for SPECT/CT). Intra-individual comparison of SPECT/CT and dPET/CT image quality, pre/post-radioembolization intrahepatic radioactivity distribution, and pre/post-radioembolization concordance was performed by a reader panel.

Results All patients had evaluable pre-radioembolization 99mTc MAA SPECT/CT, post-radioembolization bremsstrahlung SPECT/CT, and post-radioembolization dPET/CT images for qualitatively assessing intrahepatic 90Y biodistribution. Given the shorter dPET image acquisition time, dPET demonstrates better image quality with exceptional 90Y-to-background contrast when compared with bremsstrahlung SPECT/CT. Digital PET images of 90Y activity also enable improved assessment of intrahepatic radioactivity distribution as well as incidence of concordance/discordance with pre-radioembolization MAA SPECT/CT when compared with bremsstrahlung SPECT/CT.

Conclusions These results demonstrate that dPET/CT technology enables faster 90Y imaging with improved image quality than current bremsstrahlung SPECT/CT approaches which can address the clinical need for more efficient and accurate imaging based assessment of 90Y biodistribution following radioembolization. The faster image acquisition time achieved with dPET/CT also enables exceptional image quality for the purposes for assessing concordance/discordance of 90Y microsphere biodistribution with pre-radioembolization MAA SPECT/CT.