Abstract No. 511 Tumor FDG avidity before and immediately following PET/CT-guided microwave ablation of liver tumors allows visualization and quantification of tumor tissue contraction

Abstract

To measure liver tumor tissue contraction effects resulting from microwave ablation (MWA) using intraprocedural 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) images obtained before and after MWA. This HIPAA-compliant, retrospective study included 36 patients (16 women, 20 men; 37-85 years old, mean age 63) who underwent PET/CT-guided MWA of 42 FDG-avid liver tumors from May 2013 to February 2018. In three of the patients undergoing MWA, three additional FDG-avid tumors were not ablated (unablated tumors were considered for separate surgical or radiation therapy). The mean preprocedure FDG dose was 8.1mCi (range 4.9-12.0mCi). The pre- and post-ablation PET/CT images were obtained with a mean FDG uptake time of 101min and 176min, respectively. PET/CT images were reviewed by two readers reading by consensus. Mean tumor-to-normal-liver standardized uptake value ratio (SUVratio), mean tumor diameter (average of short and long axis), and automated tumor metabolic volume were measured for each tumor on both the pre and post-ablation PET images. Presence of central tumor necrosis on PET/CT images prior to ablation was documented. A two-tailed paired t-test was used to analyze differences in these metrics before and after ablation. Comparing intraprocedural pre and post ablation PET images, the mean SUVratio (tumor-to-normal-liver) increased from 4.9 to 7.1, or 44% (p < 0.001). The mean tumor diameter decreased from 22.5mm to 16.4mm, or 27% (p < 0.001). The mean tumor volume decreased from 10.5 cm3 to 5.9 cm3, or 44% (p < 0.001). For the three centrally necrotic tumors, the mean tumor diameter decrease was only 11% (p < 0.05) and the mean tumor volume decrease (20%) was not significant (p = 0.13). No significant changes in mean tumor diameter (p = 0.42) and mean tumor volume (p = 0.65) were seen in the three unablated tumors. Intraprocedural PET images of FDG-avid liver tumors allow visualization and quantification of the tissue contraction effects of microwave ablation during FDG PET/CT-guided procedures. The ability to visualize the contracted tumor may be relevant when intraprocedural PET/CT imaging techniques are used to assess the ablation margin.