Mass transfer during freezing in rat prostate tumor tissue

Cryosurgery for treating prostate cancer is hampered by art incomplete unde rstanding of the mechanisms whereby tissue destruction is achieved during f reezing, The two known biophysical mechanisms of injury, intracellular ice formation and cellular dehydration injury, (solute effects), have not been quantified within tumor tissue. Freeze substitution microscopy, and a diffe rential scanning calorimeter (DSC) were used to quantify freeze-induced deh ydration within Dunning AT-1 rat prostate tumor tissue. Stereological analy sis of histological tumor sections was used to obtain the initial cellular (V-o), interstitial, ann vascular volumes of the AT-I tumor tissue. A Boyle -van't Hoff (BVH) plot was then constructed by, examining freeze substitute d micrographs of equilibrium cooled tissue slices to obtain the osmotically inactive cell volume, V-b = 0.25V(o). Obtaining dynamic cellular water tra nsport information from the freeze substitution microscopy data proved diff icult because of the artifact added by the high interstitial volume (simila r to 35%). Since the DSC technique does not suffer from this artifact, a mo del of water transport was fit to the DSC water transport data at 5 degrees , 10 degrees and 20 degrees C/min to obtain the combined best fit membrane permeability parameters of the embedded AT-1 tumor cells, assuming either a Krogh cylinder geometry or a spherical cell geometry. Numerical simulation s were also performed to generate conservative estimates of intracellular i ce volume (IIV) in the tumor tissue at various cooling rates typical of tho se EXPERIENCED during cryosurgery (less than or equal to 100 degrees C/min) . Water transport data in tumor systems with significant interstitial space s can be obtained by using histology and the low-temperature microscopy met hods to obtain the initial and final tissue cell volumes, respectively and the DSC technique to obtain the dynamic volume changes during freezing.