Objectives. To determine the comparative freezing; ability of the Cryo
tech (CT) and AccuProbe (CMS) cryosurgical systems. Methods. Four cond
itions designed to model clinical situations were produced: (1) Single
-probe performance in water at 17 degrees C; (2) five-probe performanc
e in water at 17 degrees C; (3) single-probe performance in gel at 22
degrees C; and (4) single-probe performance in bovine liver. Parameter
s evaluated included temperatures at various time points (rates to and
final low temperature), configuration of a freeze zone, and shaft fre
ezing characteristics. In addition, isotherms were measured at predete
rmined distances from the center of the freeze zone. Results. Both sys
tems 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 prob
e surface temperature. In gel, the CMS probe increased freeze volume f
ourfold versus a twofold increase for the CT probe. In bovine liver, t
here was nearly equivalent performance with respect to geometry of the
freeze ball. Extrapolation of the CT cooling curve indicated temperat
ure 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; th
e CT configuration was more cylindrical. CMS probe (equivalent diamete
r) tip temperatures were on average 100 degrees C lower. Conclusions.
Our tests demonstrated differences between the CMS and CT probe. The m
ajor 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 equ
ivalent freezing temperatures to the CMS probe, albeit with a more sph
erical shape. However, these in vitro systems may not adequately refle
ct varied prostate morphology. Further research is under way to determ
ine if these differences affect relative efficacy of cryotherapy of th
e prostate.