Optimization of imaging parameters for Yttrium-90 bremsstrahlung emission computed tomography after selective internal radiotherapy

Yttrium-90 labeled microspheres based selective internal radiotherapy ( 90 Y-SIRT) is an established local-regional therapy for unresectable hepatocellular carcinoma (HCC) which demonstrating significant survival improvements in multiple clinical trials. Post therapeutic 90 Y imaging is essential for in vivo 90 Y microspheres biodistribution evaluation and absorbed dose estimation. We aim to study the effects of 90 Y bremsstrahlung imaging parameters including energy window center, width and acquisition time on the quality of 90 Y SPECT/CT to provide optimal imaging conditions after 90 Y-SIRT. Using the NEMA IEC NU2 body phantom and Siemens Symbia™ T16 SPECT/CT scanner equipped with a high-energy general-purpose collimator (HEGPC), seven energy window settings and two acquisition times (20s / frame and 40s / frame) were investigated and analyzed. 90 Y bremsstrahlung imaging with 94 keV ± 40% energy window limits and 20s / frame acquisition time demonstrated the highest contrast-to-noise ratio (CNR) and contrast recovery coefficient (Q H ). In further analysis using a single hot sphere (diameter = 22 mm), the imaging parameter combination of 94 keV ± 40% and 20s / frame showed the lowest coefficient of variation (COV), while the residual count error in the lung insert ( \(\:\:{C}lung\) ) remained at a relative low level among all imaging parameters. For HEGPC, 94 keV ± 40% with 20s / frame is the optimal acquisition parameter for 90 Y BECT imaging, while 80 keV ± 30% is also good energy window center and widths.