Quantitative Comparison of PET and Bremsstrahlung SPECT for Imaging the In Vivo Yttrium-90 Microsphere Distribution after Liver Radioembolization

Abstract

BackgroundAfter yttrium-90 (90Y) microsphere radioembolization (RE), evaluation of extrahepatic activity and liver dosimetry is typically performed on 90Y Bremsstrahlung SPECT images. Since these images demonstrate a low quantitative accuracy, 90Y PET has been suggested as an alternative. The aim of this study is to quantitatively compare SPECT and state-of-the-art PET on the ability to detect small accumulations of 90Y and on the accuracy of liver dosimetry.Methodology/Principal FindingsSPECT/CT and PET/CT phantom data were acquired using several acquisition and reconstruction protocols, including resolution recovery and Time-Of-Flight (TOF) PET. Image contrast and noise were compared using a torso-shaped phantom containing six hot spheres of various sizes. The ability to detect extra- and intrahepatic accumulations of activity was tested by quantitative evaluation of the visibility and unique detectability of the phantom hot spheres. Image-based dose estimates of the phantom were compared to the true dose. For clinical illustration, the SPECT and PET-based estimated liver dose distributions of five RE patients were compared. At equal noise level, PET showed higher contrast recovery coefficients than SPECT. The highest contrast recovery coefficients were obtained with TOF PET reconstruction including resolution recovery. All six spheres were consistently visible on SPECT and PET images, but PET was able to uniquely detect smaller spheres than SPECT. TOF PET-based estimates of the dose in the phantom spheres were more accurate than SPECT-based dose estimates, with underestimations ranging from 45% (10-mm sphere) to 11% (37-mm sphere) for PET, and 75% to 58% for SPECT, respectively. The differences between TOF PET and SPECT dose-estimates were supported by the patient data.Conclusions/SignificanceIn this study we quantitatively demonstrated that the image quality of state-of-the-art PET is superior over Bremsstrahlung SPECT for the assessment of the 90Y microsphere distribution after radioembolization.

SPECT/CT image‐based dosimetry for Yttrium‐90 radionuclide therapy: Application to treatment response

“…Elschot et al. demonstrated that time‐of‐flight PET‐based dose estimates were more accurate than SPECT‐based dose estimates, which produced large underestimations in high‐dose regions 15. Conversely, Yue et al.…”

“…Despite positive results from published studies,6, 7 the reported doses assume that the activity distribution within the treatment volume is uniform. Quantitative patient‐specific 90 Y dosimetry has been studied using bremsstrahlung single photon emission computed tomography (SPECT)/computed tomography (CT) 8, 9, 10, 11 and positron emission tomography (PET)/CT 12, 13, 14, 15, 16. However, such dosimetric studies have utilized research software that is not readily available to the medical community and have not illustrated scenarios where voxel‐based dosimetry could be used to predict treatment response.…”

Semi-Quantitative Analysis of Post-Transarterial Radioembolization 90Y Microsphere Positron Emission Tomography Combined with Computed Tomography (PET/CT) Images in Advanced Liver Malignancy: Comparison With 99mTc Macroaggregated Albumin (MAA) Single Photon Emission Computed Tomography (SPECT)

“…When combined with SPECT imaging, bremsstrahlung SPECT/CT showed more accurate anatomical localization of 90 Y microspheres [26]. In spite of these characteristics of the bremsstrahlung image, the major drawbacks are the low spatial resolution and long image acquisition time, which would lead to lower tumor-to-normal ratios compared to the 99m Tc MAA images [27].…”

“…Other reports revealed that 90 Y PET/CT after 90 Y microsphere treatment has better image quality than 90 Y bremsstrahlung SPECT images [15,26]. The higher resolving power of 90 Y PET/CT might have the potential to predict treatment responses more accurately.…”

Multiagent imaging of liver tumors with reference to intra-arterial radioembolization

“…6). Elschot and colleagues [49] showed that the image quality of PET is superior to bremsstrahlung SPECT for the assessment of 90 Y-microsphere distribution after RE. PET showed higher contrast recovery coefficients than SPECT.…”