3:20 PM Abstract No. 344 In vivo determination of cryoablation size after an abbreviated single 15-minute freeze protocol in swine hepatic and renal tissue in comparison to the conventional 10-8-10 minute freeze-thaw-freeze protocol

Abstract

To determine the lethal cryoablation size of a single 15-minute freeze protocol and compare it with that of the conventional 10-minute freeze, 8-minute active thaw, 10-minute freeze cycle (10-8-10) in swine liver and kidney. Percutaneous CT-guided cryoablation was performed in 5 swine livers and kidneys. In each organ, one ablation (2 probes) was performed utilizing the 10-8-10 minute cycle and a second utilizing the single 15-minute cycle. When the “ice-ball” was maximal, 10 cc of India Ink was arterially infused into the organ. The two ablations were timed to end simultaneously so that the unfrozen tissue surrounding both ablation zones was stained at maximal ablation volume. Histologic analysis was performed by a pathologist. The ablation length (long axis of the cryoprobe tract) and maximum width (perpendicular to the cryoprobe track) were measured and the tissues were fixed in formalin. Histopathologically determined ablation length in the 10-8-10 samples was 5.00 ± 0.75 cm and 6.55 ± 0.55 cm for kidney and liver tissue, respectively. For the 15-minute single cycle the respective sizes were 4.96 ± 0.32 cm and 6.85 ± 0.49 cm. Similarly, ablation width in the 10-8-10 samples was 3.95 ± 0.17 cm and 4.5 ± 0.3 cm for kidney and liver, respectively, in the 10-8-10 samples and 4.00 ± 0.44 cm and 4.3 ± 0.28 cm, for kidney and liver, respectively, in the 15-minute samples. Neither ablation length nor width (and consequently volume) were significantly different between the cryoablation protocols. In addition, this was true in both kidney and liver tissue. However, ablation length and width were significantly smaller in the kidney when compared to the liver, for each cryoablation protocol. This observation can be explained by the higher tissue perfusion in the kidney compared to the liver (fourfold), and the role this perfusion plays in heat exchange within the tissue (the heat pump effect). An abbreviated, single 15-minute cryoablation results in an identical ablation size to that of the conventional 10-8-10 minute protocol, regardless of tissue. A larger cryoablation zone observed in hepatic tissue can potentially be explained by differences in tissue perfusion.