Optimizing the Protocol for Pulmonary Cryoablation: A Comparison of a Dual- and Triple-Freeze Protocol

The purpose of this study was to compare a double freeze–thaw protocol to a triple freeze–thaw protocol for pulmonary cryoablation utilizing an in vivo porcine lung model. A total of 18 cryoablations were performed in normal porcine lung utilizing percutaneous technique with 9 each in a double- (10-5-10) and triple-freeze (3-3-7-7-5) protocol. Serial noncontrast CT images were obtained during the ablation. CT imaging findings and pathology were reviewed. No imaging changes were identified during the initial freeze cycle with either protocol. However, during the first thaw cycle, a region of ground glass opacity developed around the probe with both protocols. Because the initial freeze was shorter with the triple freeze–thaw protocol, the imaging findings were apparent sooner with this protocol (6 vs. 13 min). Also, despite a shorter total freeze time (15 vs. 20 min), the ablation zone identified with the triple freeze–thaw protocol was not significantly different from the double freeze–thaw protocol (mean diameter: 1.67 ± 0.41 cm vs. 1.66 ± 0.21 cm, P = 0.77; area: 2.1 ± 0.48 cm² vs. 1.99 ± 0.62 cm², P = 0.7; and circularity: 0.95 ± 0.04 vs. 0.96 ± 0.03, P = 0.62, respectively). This study suggests that there may be several advantages of a triple freeze–thaw protocol for pulmonary cryoablation, including earlier identification of the imaging findings associated with the ablation, the promise of a shorter procedure time or larger zones of ablation, and theoretically, more effective cytotoxicity related to the additional freeze–thaw cycle.