The speed of ice growth as an important indicator in cryosurgery

PURPOSE: We consider the speed of ice growth as an indicator of the speed of cooling and investigated its impact on the factors at the cell death boundary in an in vitro simulated cryosurgical system. MATERIALS AND METHODS: PC-3 cells were cultured in culture plates and simulated cryosurgery was performed under different speeds of ice growth using an in vitro simulated cryosurgical system. The freezing front was closely monitored. Cells were fixed and stained 24 hours after cryosurgery. The distance from the cell death boundary to the ice front was measured and defined as the distance gap. It was correlated with the speed of ice growth. Temperature history at the cell death boundary was retrieved and also correlated with the speed of ice growth. RESULTS: A high correlation between the speed of ice growth and the temperature gradient plus an inverse correlation between the speed of ice growth and the distance gap were found. The distance gap narrowed when the speed of ice growth was around 3 mm per minute but widened when the speed of ice growth was slower than 1.5 mm per minute. CONCLUSIONS: Changes in ice growth speed indicate changes in the temperature gradient, and the distance between the ice front and the cell death boundary. Different treatment end points should be chosen according to the speed of ice growth to increase accurate cell killing.