Optimizing Colorectal Liver Metastasis Ablation through Metabolic Imaging, Margin Assessment, and Biopsy (The...

Background Real-time methods are needed for intraprocedural detection of residual tumors and incomplete thermal ablation (TA) to allow immediate retreatment and tumor eradication. Purpose To validate a TA workflow for detecting and immediately ablating residual viable colorectal liver metastases (CLMs). Materials and Methods This prospective single-center trial enrolled participants who underwent PET/CT-guided microwave CLM ablation from November 2019 to February 2023. The minimal ablation margin (MM) was calculated in all directions. Biopsies were obtained from the ablation zone (AZ) center and margin, with rapid tissue assessment for viable tumor (VT) cells using imprint cytology and fluorescent viability staining. Immediate reablation was performed if any of the following criteria were met: MM less than 5 mm at contrast-enhanced CT, residual PET-avid tumor, and/or VT cells at rapid tissue assessment. Gray-model statistics quantified the MM and VT impact on local tumor progression subdistribution hazard amid the competing risk of death. Results Seventy-seven participants (median age, 56 years [IQR, 47-64.5 years]; 39 male participants) underwent ablation in 104 CLMs. Overall, 15 of 104 (14%) CLMs underwent immediate reablation per the criteria (12 of 15, VT; seven of 15, MM <5 mm; and four of 15, residual fluorodeoxyglucose avidity). After reablation, all 12 initially VT-positive AZs underwent repeat biopsies with negative findings. Five of seven MMs less than 5 mm in AZs increased to greater than 5 mm after reablation. All four CLMs that underwent reablation due to PET/CT findings had AZs positive for VT, and one had MM less than 5 mm. MM greater than 5 mm protected against local tumor progression (LTP) (subdistribution hazard ratio, 0.12; 95% CI: 0.05, 0.30; P < .001). There was no LTP for MMs greater than 10 mm. The cumulative LTP incidence at 1, 2, and 3 years for participants with biopsy-proven completely ablated CLMs with MM greater than 5 mm was 7%, 12%, and 12%, respectively. Conclusion MM remained a critical technical factor affecting tumor control; the proposed multimodal comprehensive AZ assessment enabled immediate onsite reablation of 14% of CLMs with initially insufficient ablation treatment and improved local tumor control after thermal ablation. ClinicalTrials.gov identifier: NCT04143516 © RSNA, 2026 Supplemental material is available for this article. See also the editorial by Georgiades in this issue.