Iceball Margin < 5 mm Is Associated with Local Failure after CT-Guided Cryoablation of cT1a Renal Cell Carcinoma

To evaluate the relationship between iceball minimal treatment margins (MTMs) and local treatment failure (LTF) after computed tomography (CT)-guided percutaneous cryoablation (PCA) of cT1a renal cell carcinoma (RCC).

Outcomes of PCA for biopsy-proven RCC (2015-2022) with ≥12 months of imaging follow-up were retrospectively reviewed. LTF was defined as residual tumor or local progression. MTM, defined as iceball extension beyond tumor margins, was measured on spatially synchronized intraprocedural and planning CT examinations. LTF cases were matched 1:2 to local controls by size and histology. Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis in the matched cohort.

Of 575 RCCs, 17 (3.0%) demonstrated LTF. Median follow-up was 1,173 days. Tumors with LTF were significantly larger than tumors with local control (29.2 mm vs 23.7 mm; P = .01), and MTM was significantly smaller in the LTF group (0.4 mm vs 7.1 mm, P < .001). ROC analysis within the matched analytical cohort demonstrated high discrimination for stratifying local failure risk (area under the curve, 0.97). The predefined 5-mm clinical threshold, defined as MTM < 5 mm indicating an insufficient margin, achieved the maximal Youden index, with sensitivity and specificity of 88.2% and 94.1%, respectively. All in-zone failures occurred with MTM < 5 mm; 2 out-of-zone progressions occurred adjacent to Gerota fascia despite MTM ≥ 5 mm.

LTFs after PCA of T1a RCC were associated with insufficient (<5 mm) iceball margins. Achieving an MTM ≥ 5 mm is strongly associated with durable local control, underscoring the importance of careful intraprocedural assessment of margins.