Laboratory and animal model evaluation of the Cryotech LCS 2000 in hepatic cryotherapy

Hepatic cryotherapy is increasingly used in the treatment of patients with multiple hepatic metastases, particularly from colorectal cancer. The Cryotech LCS 2000 system, with insulated shaft-circulated liquid nitrogen probes, was designed for this purpose and was evaluated on the bench and in an animal model. The 9-mm probe was considerably more effective than the 5-mm probe when judged on time to create an iceball of a given diameter. The use of thawing gas reduced the time until the probe could be removed from 25 to 5 min but heated gas only produced a further reduction of 2 min. In the animal model, significant reduction in treatment times occurred with vascular inflow occlusion. The zone of necrosis as a percentage of the original iceball diameter was significantly higher following a twin freeze/thaw cycle. The relationship of the edge of the iceball to the eventual zone of hepatic necrosis was studied using different unabsorbable markers. India ink and sutures proved unreliable but a Teflon cannula was more successful and the margin was only of the order of 2 mm. The discrepancy between this observation and the percentage of the original iceball diameter which apparently becomes necrotic (64 and 82%) for single- and double-freeze lesions, respectively, suggests that the cryolesion undergoes shrinkage within 1 month and that the diameter of necrosis underestimates the true zone of destruction.