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SIR 2025

General IR

Interventional Oncology

Scientific Session

Session: Interventional Oncology - Ablation 1

Lethal Isotherm Ratio to Standardize the Comparison of Cryoablation Needles and Systems

Sunday, March 30, 2025
3:27 PM – 3:36 PM CT
Location: Music City Center, 209 ABC
Purpose: To establish the lethal isotherm ratio (LIR), a metric standardizing the comparison of cryoprobes and technologies on their intrinsic characteristics and performance.

Materials and Methods: A total of 216 isotherms at the freezing front, -20°C, and -40°C, measured in ultrasonic gels under various conditions and certified by the Food and Drug Administration were obtained from Argon-based Joule-Thompson systems A and B, and liquid nitrogen-based system C. The ratio between the widths at the freezing front, and of isotherms at -20°C or -40°C were calculated to obtain the respective LIRs, which were compared among the systems, needles and combinations of needles after linear regression.

Results: Strong linear correlations of isotherms were observed for all systems, ranging from ρ:0.8804 to ρ:0.9894 (all p=.0001). For single needle, LIRs of system C were in mean 80.6%+/-3.9 at -20°C and 60.3%+/-5.6 at -40°C, significantly higher than systems A (69.6%+/-4.6 and 44%+/-6.3, respectively, both p=.0001) and B (69.6%+/-7, p=.0001, and 51.4%+/-7.4, p=.0002, respectively). LIRs were not significantly different between system C and clusters of needles of system A (79.3%+/-4.2, p=.486, and 60.9%+/-8.3, p=.656, respectively). The intersections of the linear regressions of systems A and C show that clusters provide higher LIRs for ice ball width above 45 mm.

Conclusion: Significant system-dependent differences in LIRs emerged, which may influence cryoprobe selection and their combinations. A single liquid nitrogen needle may offer superior LIR for ice balls smaller than 45mm in width, whereas clusters of needles are required beyond.