Lethal isotherm ratio to standardize the comparison of cryoablation needles and systems

Abstract Purpose To establish the lethal isotherm ratio (LIR), a standardized metric for comparing cryoprobes and technologies based on their performance. Materials and methods Isotherms at the freezing front (0°C), -20°C, and -40°C, measured in ultrasonic gels under standardized conditions and FDA-certified, were obtained from Argon-based Joule-Thompson systems A and B, and liquid nitrogen-based system C ( n = 216). The LIR—defined as the ratio between isotherm widths at lethal temperatures (-20°C/-40°C) and the visible freezing front (0°C)—was calculated to compare systems, single needles, and needle combinations. Results Strong linear correlations between isotherms were observed across all systems (ρ:0.880–0.999, p = .0001). System C showed significantly higher LIRs (80.6% ± 3.9 at -20°C [95%CI: 79.8–81.4%], 60.3% ± 5.6 at -40°C [95%CI: 59.2–61.4%]) than systems A (69.6% ± 4.6 [95%CI: 68.7–70.5%], 44% ± 6.3 [95%CI: 42.8–45.2%]; both p = .0001) and B (69.6% ± 7 [95%CI: 67.2–72.0%], 51.4% ± 7.4 [95%CI: 48.9–53.9%]; p = .0001, p = .0002). Linear regression analysis demonstrated that clustered needles provide higher LIRs for ice balls exceeding 45mm width. Conclusion A single liquid nitrogen needle offers superior LIR for ice balls <45mm, whereas needle clusters are more effective beyond this threshold. LIR might provide clinicians a standardized approach to optimize system selection, potentially improving procedural outcomes and reducing local recurrence rates.