THERMAL GRADIENTS AND CRYOSURGICAL PROBE PERFORMANCEFebruary 1997
John Bauhst, H. Ma, C-M Zhang, A. Gage
SUNY at Binghamton and Buffalo and Cryomedical Sciences, Inc., Rockeville, MD USA
Successful cryosurgery requires knowledge of cryosurgical probe performance. Our objective was to determine the freezing capability of cryosurgical probes and to evaluate this capability in terms of the factors in the freeze/thaw cycle known to produce a destructive response.
Method - Cryosurgical probes, 3.4 mm and 8 mm in diameter, were placed in agelatin bath and cooled to tip
temperatures of -195 °C, -175 °C and -100 °C by cryosurgical apparatus (CMS AccuProbe® System).
Results - The 8 mm probe achieved a tip temperature (PT) of -195°C in 3 minutes and produced a 7cm iceball in 20 minutes. The 8mm probe used with a PT of -100°C produced a 5.5cm iceball in 20 minutes. The -40°C isotherm was 5mm inside of the 0°C isotherm with PT of -195°C, 7mm inside of the 0°C isotherm with a PT of -175°C, and 13mm inside o the 0°C isotherm with a PT at -100°C. The 3.4mm probe with PT at -175°C produced a 5cm iceball in 20mins. Used at -100°C, the resultant iceball was 4cm in 20 minutes. The -40°C isotherm with PT at -175°C was 10mm from 0°C isotherm. With PT at -100°C, the -40°C isotherm was only 4mm from the probe, 16mm inside of the 0°C isotherm.
Conclusions - The colder the probe temperature, the faster the rate of freezing and the larger the frozen volume. The colder the probe and the faster the freezing rate, the closer the -40°C isotherm is to the 0°C isotherm. Probe temperatures of -175°C and colder are needed to create lethal temperatures more than 2cm from the probe, as is required for many cancers.