Sub-5 mm Iceball Margin Predicts Local Failure After Renal Cryoablation

In 575 cT1a renal cell carcinomas treated with CT-guided cryoablation, an iceball margin <5 mm identified local treatment failure with 88% sensitivity and 94% specificity (AUC 0.97). All in-zone failures had margins <5 mm; achieving ≥5 mm was strongly tied to durable control.

• Retrospective matched case-control study (575 RCCs, 2015–2022; 17 local failures matched 1:2 to controls); median follow-up 1,173 days; local treatment failure rate 3.0%.
• Tumors that failed were larger (29.2 vs. 23.7 mm, p=0.01) and had markedly smaller minimal treatment margins (0.4 vs. 7.1 mm, p<0.001); the 5-mm threshold maximized the Youden index (AUC 0.97).
• Key limitation: single-center retrospective design with a small failure cohort (n=17), limiting generalizability; two out-of-zone progressions near Gerota's fascia occurred despite adequate margins, suggesting some failures are not margin-related.

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