PET/CT and SPECT/CT imaging of ⁹⁰Y hepatic radioembolization at therapeutic and diagnostic activity levels: Anthropomorphic phantom study

Purpose Prior to Y-90 radioembolization procedure, a pretherapy simulation using Tc-99m-MAA is performed. Alternatively, a small dosage of Y-90 microspheres could be used. We aimed to assess the accuracy of lung shunt fraction (LSF) estimation in both high activity Y-90 posttreatment and pretreatment scans with isotope activity of similar to 100 MBq, using different imaging techniques. Additionally, we assessed the feasibility of visualising hot and cold hepatic tumours in PET/CT and Bremsstrahlung SPECT/CT images. Materials and methods Anthropomorphic phantom including liver (with two spherical tumours) and lung inserts was filled with Y-90 chloride to simulate an LSF of 9.8%. The total initial activity in the liver was 1451 MBq, including 19.4 MBq in the hot sphere. Nine measurement sessions including PET/CT, SPECT/CT, and planar images were acquired at activities in the whole phantom ranging from 1618 MBq down to 43 MBq. The visibility of the tumours was appraised based on independent observers' scores. Quantitatively, contrast-to-noise ratio (CNR) was calculated for both spheres in all images. Results LSF estimation. For high activity in the phantom, PET reconstructions slightly underestimated the LSF; absolute difference was <1.5pp (percent point). For activity <100 MBq, the LSF was overestimated. Both SPECT and planar scintigraphy overestimated the LSF for all activities. Lesion visibility. For SPECT/CT, the cold tumour proved too small to be discernible (CNR <0.5) regardless of the Y-90 activity in the liver, while hot sphere was visible for activity >200 MBq (CNR>4). For PET/CT, the cold tumour was only visible with the highest Y-90 activity (CNR>4), whereas the hot one was seen for activity >100 MBq (CNR>5). Conclusions PET/CT may accurately estimate the LSF in a Y-90 posttreatment procedure. However, at low activities of about 100 MBq it seems to provide unreliable estimations. PET imaging provided better visualisation of both hot and cold tumours.