Feasibility of Accelerating Yttrium-90 PET by Optimizing PET Volume Overlap

Objectives Yttrium-90 (90Y) microsphere radioembolization is increasingly being used as targeted treatment of unresectable liver malignancies. While SPECT of 90Y bremsstrahlung is still the standard of care imaging modality for biodistribution, time of flight PET has also been demonstrated for post-radioembolization imaging with better spatial resolution and improved quantification especially for dosimetry however being limited by long acquisition times due to low count densities. This study investigated the feasibility of accelerating PET acquisition by reducing and optimizing PET volume overlap to further improve patient comfort and achieve short scan times.

Methods An ongoing clinical validation trial was initiated to investigate the feasibility of reducing PET volume overlap for 90Y imaging. PET/CT of 5 patients, 26±2 hours post 90Y microsphere radioembolization (3.1±0.2 GBq into hepatic lobes) were performed on a Gemini TF 64 system (system default PET overlap: 53%) with 7min/bed from diaphragm downwards to cover the entire liver using 40% and 20% PET overlap, respectively. All coincidence events were recorded in listmode. PET data was reconstructed using a 3D TOF OSEM algorithm with a voxel size of 4 x 4 x 4 mm3. Images were blinded reviewed by a reader panel. Quantitative assessment of volumes and total activity of 90Y microsphere biodistributions for each of the PET data sets was performed.

Results The 90Y PET data demonstrated no significant impact on the visual score between 40% and 20% overlap. The 20% overlap approach saved ~33% table time compared to using 40% overlap. Quantitative volume segmentation assessment resulted in equivalent volume determinations of 90Y biodistributions (variances=0.5% ±5.0%). No significant counts variance was found between both acquisitions (variances=0.5%±1.3%).

Conclusions 90Y PET imaging can be considerably accelerated by reducing PET volume overlap as is clinically demonstrated in this trial without degradation of image quality or significantly impacting quantification. This will enable to performance of 90Y PET with established clinical time slots.