The thermal stress fields of the target tissues during cryosurgery using two kinds of cryoprobe capable of both cooling and heating(the new type combined cryosurgery/hyperthermia cryoprobe and the Endocare cryoprobe)were studied comparatively.The intrinsic merits of the new type cryoprobe were revealed as compared with the Endocare cryoprobe from the point of view of thermal stress by studying the commonness and difference between these two kinds of cryoprobes.The enthalpy form of the classical bioheat equation coupled with the stress equations was solved by using the commercial software Ansys (version 7.0).The tissues were treated as nonideal materials freezing over a temperature range

and their thermophysical properties were taken as temperature dependent.Volumetric expansion associated with phase change of the tissue water appearing in this study was the main reason for the thermal stress concentration

and the thermal gradient might also have a minor effect on thermal stress.Thermal stress concentration would appear in the phase change region for both cryoprobes.The new type combined cryosurgery/hyperthermia cryoprobe could generate a much lower temperature and a wider frozen region

a much wider region that might experience stress concentration

and have a larger killing radius.Apparent thermal strain could be observed during the cryosurgery processes.