749 - Optimizing Ablation Outcomes in Small CLM: The Role of 3D Margin Assessment, PET/CT, and Rapid Histopathology

Learning Objectives: To optimize ablation outcomes using minimal ablation margin (MM) assessment, metabolic imaging, and histopathological confirmation.

Background: Thermal ablation (TA) is recommended for selected patients with colorectal liver metastases (CLM) ≤ 3cm and limited disease. However, there is no universal consensus on the routine implementation of all confirmatory techniques in standard ablation practice.

Clinical Findings/Procedure Details: A MM ≥5 mm is critical for curative effect. 3D registration software enables semi-automatic tumor contouring and margin generation (5 and 10 mm) on pre-procedural triphasic contrast-enhanced CT (ceCT), facilitating accurate image registration with immediate post-ablation ceCT with utilization of reproducible anatomic landmarks, which surpasses conventional 2D review. This allows prompt re-ablation of areas with MM < 5 mm. Available approaches include intensity-based algorithms to account for thermal alteration in tissue. Split-dose positron emission tomography (PET)/CT-guided ablation uses one-third (4 mCi) of the diagnostic dose of fluorodeoxyglucose (FDG) for accurate tumor localization over 60–120 minutes. Following completion of ablation, the remaining dose (8 mCi) is administered. Residual FDG-avid foci within the ablation zone can be immediately re-ablated. CT hepatic arteriography involves selective catheterization of the common or proper hepatic artery for repeated injection of small volumes (20 mL) of contrast. Tumors typically appear as a contrast-enhancing ring with a hypoattenuating core, or as an incomplete hyperattenuating ring in cases of tumor progression after local treatment. Post-ablation contrast injection highlights the ablation zone and any residual tumor. Immediate post-ablation biopsies can identify residual viable tumor cells within or adjacent to the ablation zone (AZ) that may result in recurrence. Samples are obtained from both the AZ center and MM. Apart from classic histopathologic assessment, immunohistochemistry and morphological staining, mitochondrial viability (MitoTracker Red) and nuclear (Hoechst) stains can serve as a real-time biomarker of residual tumor viability within 30 minutes of acquisition.

Conclusion and/or Teaching Points: 3D software-based validation, together with metabolic and histopathological confirmation of ablation completeness, is feasible and may enhance oncologic outcomes, particularly when ablation is employed as an alternative to resection curative intend treatment.