A comparative assessment of cryosurgical devices: application to prostatic disease

OBJECTIVES: To determine the comparative freezing ability of the Cryotech (CT) and AccuProbe (CMS) cryosurgical systems. METHODS: Four conditions designed to model clinical situations were produced: (1) Single-probe performance in water at 17 degrees C; (2) five-probe performance in water at 17 degrees C; (3) single-probe performance in gel at 22 degrees C; and (4) single-probe performance in bovine liver. Parameters evaluated included temperatures at various time points (rates to and final low temperature), configuration of a freeze zone, and shaft freezing characteristics. In addition, isotherms were measured at predetermined distances from the center of the freeze zone. RESULTS: Both systems provided freezing of various media under operational conditions. In water, the CMS 3-mm probe delivered more rapid freezing temperature rates than the 3-mm CT probe, with a 110 degrees C difference in probe surface temperature. In gel, the CMS probe increased freeze volume fourfold versus a twofold increase for the CT probe. In bovine liver, there was nearly equivalent performance with respect to geometry of the freeze ball. Extrapolation of the CT cooling curve indicated temperature equivalence at 30 minutes. A larger shaft diameter 4.9-mm CT probe produced results similar to the CMS probe in all the tested media. In addition, the freeze configuration of the CMS probe was spherical; the CT configuration was more cylindrical. CMS probe (equivalent diameter) tip temperatures were on average 100 degrees C lower. CONCLUSIONS: Our tests demonstrated differences between the CMS and CT probe. The major differences are in the configuration of the freeze zone and shaft freezing. In equivalent conditions, the CMS 3-mm probe delivered more rapid cooling rates, a more spherical freeze ball, and lower absolute temperatures than the CT 3-mm probe. The larger CT probe produces equivalent freezing temperatures to the CMS probe, albeit with a more spherical shape. However, these in vitro systems may not adequately reflect varied prostate morphology. Further research is under way to determine if these differences affect relative efficacy of cryotherapy of the prostate.