Experimental Study on Pulmonary Cryoablation in a Porcine Model of Normal Lungs

Objective of this study is to analyze the range of necrosis after using different freezing times and freeze-thaw cycles during percutaneous cryosurgery, in order to create a suggestion for optimizing the technique for lung cryoablation. Six healthy pigs were given a CT scan and histological investigation after percutaneous cryosurgery on both lungs. Three cryoprobes were inserted into both the left and right lungs of each pig, respectively. Cryoablation was performed with two cycles of an active 10-minute freezing using argon in the left lung, each freeze followed by an active 5-minute thaw using helium. In contrast to the left lung cryoablation, the right lungs underwent 3 cycles of freeze/thaw, the first and second cycles consisted of an active 5-minute freezing followed by an active 5-minute thaw, and the third cycle of 10-minute freezing and an active 5-minute thaw. The CT imaging change of an ice ball was continuously observed. The lung tissues were taken 4 hours after cryosurgery on day 3 and on day 7, respectively, for pathological observation. One pig presented acute symptoms including bradycardia and hypothermia 30 minutes after cryosurgery, and died 4 hours after the freezing, and the other 5 pigs experienced a weak condition for 4-6 hours and then exhibited relatively normal behavior and regularly took food. The freezing area (ice ball) on CT imaging during the cryoablation grew gradually in relation to the increase over time, and along with the increase in the number of cycles. The size of the cryolesion on the lung samples became larger than the ice ball during cryosurgery, regardless of whether 2 or 3 freeze-thaw cycles were performed. The area of necrosis histologically gradually increased for the time being. Percutaneous cryosurgery on the lung can achieve complete ablation of targeted tissue. Three freeze-thaw cycles are recommended, and the range of cryoablation may not be mandatory "1 cm safe border" during cryosurgery in order to avoid harming the organ and tissue which is close to the cancer. Correct use of the technique is especially important to treat the lung neoplasms, especially the malignant tumors, which are close to the heart and large vessels.