Optimal Freeze Cycle Length for Renal Cryotherapy

Abstract

Purpose To our knowledge the optimal freeze cycle length in renal cryotherapy is unknown. Ten-minute time based freeze cycles were compared to temperature based freeze cycles to −20C. Materials and Methods Laparoscopic renal cryotherapy was performed on 16 swine. Time based trials consisted of a double 10-minute freeze separated by a 5-minute thaw. Temperature based trials were double cycles of 1, 5 or 10-minute freeze initiated after 1 of 4 sensors indicated −20C. A 5-minute active thaw was used between freeze cycles. Control trials consisted of cryoneedle placement for 25 minutes without freeze or thaw. Viability staining and histological analysis were done. Results There was no difference in cellular necrosis between any of the temperature based freeze cycles (p = 0.1). Time based freeze cycles showed more nuclear pyknosis, indicative of necrosis, than the 3 experimental freeze cycles for the renal cortex (p = 0.05) but not for the renal medulla (p = 0.61). Mean time to −20C for freeze cycle 1 was 19 minutes 10 seconds (range 9 to 46 minutes). In 4 of 21 trials (19%) −20C was never attained despite freezing for 25 to 63 minutes. Conclusions There was no difference in immediate cellular necrosis among double 1, 5 or 10-minute freeze cycles. Cellular necrosis was evident on histological analysis for trials in which −20C was attained and in freeze cycles based on time alone. With a standard 10-minute cryoablation period most treated parenchyma 1 cm from the probe never attained −20C. Cell death appeared to occur at temperatures warmer than −20C during renal cryotherapy.

Renal mass cryoablation: Melting time analysis of radiographic ice-ball after 5-minute active thawing by using serial ultrasound

“…Although the time-based optimal freezing per-cycle is relatively wellestablished (i.e., 10-min) [4,[11][12][13], there is still uncertainty on optimal duration of final thawing cycle before the cryoneedle removal. Nevertheless, 5-10 min of thawing is usually applied for renal PCA [14,15].…”

Multipoint Thermal Sensors Associated with Improved Oncologic Outcomes Following Cryoablation

“…MTS needle probes are 1.47 mm (17-gauge) in diameter and provide four temperature readings marked at 5, 15, 25, and 35 mm from the tip of the needle with an accuracy of -5°C. Based on prior literature, 18 the attainment of the adequate freeze temperature was defined as a reading of -20°C on the 5, 15, 25, and/or 35 mm marks on the MTS needle, at the point best representing the tumor margin. After -20°C was attained, a 10-minute freeze was performed followed by a 6minute thaw.…”

“…Most studies report satisfactory ablation of tumors with temperatures of -16°C to -20°C, [15][16][17][18] although some earlier studies recommended -40°C to destroy cancer cells. 19 While temperature sensors to monitor temperature attainment have been used previously in both urologic and nonurologic cryosurgery, they are not currently standard in CA procedures of the SRM.…”