Optimal freeze cycle length for renal cryotherapy.

Area of Science:

• Urology
• Surgical Innovation
• Cryobiology

Background:

• Renal cryotherapy is a minimally invasive technique for treating renal tumors.
• The optimal parameters for renal cryotherapy, specifically freeze cycle duration, are not well-established.
• Understanding freeze dynamics is crucial for maximizing efficacy and minimizing collateral damage.

Purpose of the Study:

• To compare the efficacy of time-based versus temperature-based freeze cycles in renal cryotherapy.
• To determine if achieving a specific temperature of -20°C is necessary for cellular necrosis.
• To evaluate the impact of different freeze cycle durations on renal parenchyma.

Main Methods:

• Laparoscopic renal cryotherapy was performed on 16 swine models.
• Time-based freeze cycles involved double 10-minute freezes with a 5-minute thaw.
• Temperature-based freeze cycles used double cycles of 1, 5, or 10 minutes, initiated when sensors reached -20°C, with a 5-minute thaw.
• Histological analysis and viability staining were used to assess cellular necrosis.

Main Results:

• No significant difference in cellular necrosis was observed between various temperature-based freeze cycles.
• Time-based freeze cycles demonstrated increased nuclear pyknosis (necrosis) in the renal cortex compared to temperature-based cycles.
• In a significant portion of trials, the target temperature of -20°C was not reached, even with extended freezing times.

Conclusions:

• Immediate cellular necrosis was comparable across different durations of temperature-based freeze cycles.
• Cellular necrosis occurred in both temperature-based and time-based freeze cycles, and in instances where -20°C was achieved.
• These findings suggest that effective cryoablation and cell death may occur at temperatures warmer than -20°C, challenging current protocols.