18F-FDG PET/CT Is an Immediate Imaging Biomarker of Treatment Success After Liver Metastasis Ablation

Abstract

The rationale of this study was to examine whether (18)F-FDG PET/CT and contrast-enhanced CT performed immediately after percutaneous ablation of liver metastases are predictors of local treatment failure at 1 y.

Methods: This Health Insurance Portability and Accountability Act-compliant, Institutional Review Board-approved retrospective study reviewed 25 PET/CT-guided thermal ablations performed from September 2011 to March 2013 on 21 patients (11 women and 10 men; mean age, 56.8 y; range, 35-79 y) for the treatment of liver metastases (colorectal, n = 23; breast, n = 1; and sarcoma, n = 1). One to 3 tumors (mean size, 2.3 cm; range, 0.7-4.6 cm; mean SUVmax, 22.7; range, 9.5-77.1) were ablated using radiofrequency (n = 16) or microwave (n = 9) energy in a single session. Immediate-postablation enhanced CT and PET/CT scans were qualitatively evaluated by 2 reviewers independently, and the results were compared with clinical and imaging outcome at 1 y. The PET/CT scans were also analyzed to determine tissue radioactivity concentration (TRC) from 3-dimensional regions of interest in the ablation zone, the margin, and the surrounding normal liver to calculate a TRC ratio, which was then compared with outcome at 1 y. Receiver operating characteristics (ROC) were used, and the maximal-accuracy threshold in predicting recurrence was calculated.

Results: Eleven (44%) of the 25 tumors recurred within 1 y. Enhanced CT did not significantly correlate with recurrence (P = 0.288). Accuracy was 64% (16/25), and the area under the ROC curve was 0.601 (95% confidence interval [95% CI], 0.387-0.789). The accuracy of the qualitative analysis of (18)F-FDG PET was 92% (23/25) (P < 0.001), and the area under the ROC curve was 0.929 (95% CI, 0.740-0.990). The mean TRC ratio was 40.6 in the recurrence group (SD, 9.2; range, 29.3-53.9) and 15.9 in the group without recurrence (SD, 7.3; range, 3-27.3). A TRC ratio of 28.3 predicted recurrence at 1 y with 100% accuracy (25/25) (P < 0.001), and the area under the ROC curve was 1 (95% CI, 0.863-1).

Conclusion: Immediate PET/CT accurately predicts the success of liver metastasis ablation at 1 y and is superior to immediate enhanced CT.

Keywords: PET/CT; imaging biomarkers; interventional radiology; thermal ablation; treatment failure.

FIGURE 1

Quantitative PET/CT image analysis. (A) Axial unenhanced CT scan of ablated zone (arrow), providing no information on treatment effectiveness. (B) Positioning of two 3-dimensional ROIs on corrected PET image: one including ablative zone and its margins and one including healthy liver. (C) Axial PET/CT image used to control position of ROI. (D) Adjustment of ROI in coronal plane to avoid including adjacent high-uptake tissue, such as kidney.

FIGURE 2

PET/CT-guided radiofrequency ablation in 47-y-old man with 22-mm metastasis from colon adenocarcinoma. (A) PET/CT image before ablation showing metastasis (arrow; SUV_max, 17). (B) Image immediately after ablation showing equivocal residual uptake (TRC ratio, 40). (C) Image at 6 mo showing obvious uptake concordant with previous findings. Residual tumor was identified, but no local treatment was proposed. (D) Image at 1 y showing similar results.

FIGURE 3

PET/CT-guided radiofrequency ablation in 44-y-old woman with 16-mm metastasis from colon adenocarcinoma. (A) PET/CT image before ablation showing metastasis (arrow; SUV_max, 13). (B) Image immediately after ablation showing no residual uptake (TRC ratio, 7.4). (C) Image at 6 mo showing no uptake, concordant with previous findings. (D) Image at 1 y showing no residual disease.