Clinical feasibility of 90Y digital PET/CT for imaging microsphere biodistribution following radioembolization

The purpose of this study was to evaluate the clinical feasibility of next generation solid-state digital photon counting PET/CT (dPET/CT) technology and imaging findings in patients following Y-90 microsphere radioembolization in comparison with standard of care (SOC) bremsstrahlung SPECT/CT (bSPECT/CT). Five patients underwent SOC Y-90 bremsstrahlung imaging immediately following routine radioembolization with 3.5 +/- 1.7 GBq of Y-90-labeled glass microspheres. All patients also underwent dPET/CT imaging at 29 +/- 11 h following radioembolization. Matched pairs comparison was used to compare image quality, image contrast and Y-90 biodistribution between dPET/CT and bSPECT/CT images. Volumetric assessments of Y-90 activity using different isocontour thresholds on dPET/CT and bSPECT/CT images were also compared. Digital PET/CT consistently provided better visual image quality and Y-90-to-background image contrast while depicting Y-90 biodistribution than bSPECT/CT. Isocontour volumetric assessment using a 1% threshold precisely outlined Y-90 activity and the treatment volume on dPET/CT images, whereas a more restrictive 20% threshold on bSPECT/CT images was needed to obtain comparable treatment volumes. The use of a less restrictive 10% threshold isocontour on bSPECT/CT images grossly overestimated the treatment volume when compared with the 1% threshold on dPET/CT images. Digital PET/CT is clinically feasible for the assessment of Y-90 microsphere biodistribution following radioembolization, and provides better visual image quality and image contrast than routine bSPECT/CT with comparable acquisition times. With further optimization and clinical validation, dPET technology may allow faster and more accurate imaging-based assessment of Y-90 microsphere biodistribution.