Three-Dimensional Margin Assessment Predicts Local Tumor Progression after Stereotactic Microwave Ablation of Small Hepatocellular Carcinoma of ≤3 cm.

PURPOSE: To evaluate the impact of the minimal ablation margin (MAM) on local tumor progression (LTP) after stereotactic microwave ablation (MWA) of small hepatocellular carcinoma (HCC) using 3-dimensional (3D) quantitative ablation margin (QAM) assessment. MATERIALS AND METHODS: This retrospective single-center study included 175 lesions in 115 patients with HCC of ≤3 cm treated with stereotactic MWA. The MAM was assessed using 3D-QAM analysis. Associations with LTP were evaluated using multivariable logistic regression. Model performance was assessed by receiver-operating characteristic (ROC) analysis and internally validated using bootstrap resampling. Sensitivity analyses included generalized estimating equations to account for clustering of lesions within patients. Additional analyses adjusted for reablation and included time-to-event analyses. RESULTS: LTP occurred in 36 of 175 lesions (20.6%). Lesions with LTP had significantly smaller margins than those without progression (2.9 vs 4.7 mm; P < .001). The MAM was a strong independent protective factor (odds ratio, 0.68 per-millimeter increase; P < .001). Right-sided lesion location was associated with increased risk (odds ratio, 2.75; P = .045), whereas multifocality was not significant. ROC analysis showed moderate discrimination (area under the curve, 0.70). Internal validation demonstrated stable model performance with an optimism-corrected area under the ROC curve of 0.73 and good calibration (slope, 0.93). Results remained consistent in sensitivity analyses using generalized estimating equations. Time-to-event analyses confirmed the MAM-LTP-free survival association. CONCLUSIONS: The MAM is a key determinant of LTP after stereotactic MWA of small HCC. Margin-based risk prediction is robust and supports the clinical use of 3D margin assessment to optimize local tumor control.