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SIR 2026

Scientific Session

Interventional Oncology

Session: AI & Imaging

289 - 3D Software Assessments Can Predict Local Tumor Progression Following Microwave Ablation in Colorectal Lung Metastases

Wednesday, April 15, 2026
11:51 AM - 12:00 PM ET
Purpose: To assess the feasibility and prognostic value of three-dimensional (3D) minimal ablation margin (MM) measurement with image registration software.

Materials and Methods: This retrospective study included 116 colorectal pulmonary metastases (median size 0.8 cm, range 0.4–2.4; 56.8% bilateral) in 88 patients [median age 54.5 years] treated with microwave ablation (June 2015–December 2021). MM were quantified in 3D using the Ablation Confirmation Software (NeuWave Medical, Madison, WI) using semi-automated registration, on immediate and 4-8 weeks post-ablation Computer Tomography (CT) scan. MM was assessed without and with the application of an intensity-based deformation algorithm (DEFA) to account for thermal changes (15% contraction). MM were independently reviewed by three interventional radiologists (two ≥5 years of experience, one fellow) for the need of additional ablation. Local tumor progression (LTP) was evaluated up to 24 months and prognosticators were analyzed with competing risk regression analysis using sub distribution hazard ratios (SHR) (STATA 17.0 SE).

Results: Local control at 12 and 24 months was 92.2% and 83.5%. Reviewer concordance was 93.1%, with 100% agreement between experienced readers; 8/116 cases (6.9%) of disagreement were resolved by unanimous consensus. MM < 5 mm were detected in 31/116 cases (26.7%) on immediate post-ablation CT, 12 (38.7%) of which developed LTP. Based on the same day 3D-margin assessment additional ablation would have been offered in 12 of the 17 (70.1%) cases that ultimately progressed. Intra-procedural MM ≥5 mm predicted local control without (SHR 0.05, p< 0.01) and with DEFA (SHR 0.36, p=0.023). MM ≥5 mm at 4–8 weeks without DEFA was not predictive (p=0.052), whereas MM ≥5 mm with DEFA was also associated with tumor control (SHR 0.23, p=0.027). The latter demonstrated the same sensitivity (82%), but inferior specificity (57% vs 83%) and lower diagnostic accuracy (60% vs 83%) compared with intra-procedural 3D assessment without DEFA. Even though 2D side-by-side assessment at 4-8 weeks CT indicated acceptable tumor coverage in all cases, 3D software suggested insufficient MM < 5 mm in 59/116 (50.9%) cases, 14 (23.7%) of which developed LTP. Proximity ≤10 mm to airway (SHR 3.57, p=0.043) and vessels ≥3 mm (SHR 3.03, p=0.035) was associated with LTP.

Conclusion: Same day image 3D Margin measurement provides the most accurate detection of MM < 5 mm and areas at risk for LTP. This information can be used to guide decisions of additional ablation within the same session.