Objectives: To determine the critical temperatures below which human prostatic tissue can be cryoablated in situ and the comparative cryoablative efficacy of single versus double-freeze cryosurgery.
Methods: Six patients with prostate cancer previously scheduled for prostatectomy underwent unilateral or bilateral cryosurgery using a single cryosurgery probe per hemiprostate. Intraprocedural interstitial prostatic temperatures were measured by thermocouple junctions placed at various radial distances from the probe. After subsequent prostatectomy, whole-mount sections of the prostate gland were subjected to histopathologic evaluation.
Results: Uniform coagulative necrosis was observed in proximity to the cryosurgery probe. The percentage of the prostate volume falling within the zone of necrosis produced by a single probe was significantly greater (P = 0.048) after a double freeze (median 13%; range 8% to 20%) than a single freeze (median 4%; range 0% to 12%). The critical temperature for cryoablation with a double freeze was -41.4 degrees C (95% confidence interval -49.9 degrees to -33.0 degrees C) compared with -61.7 degrees C (95% confidence interval -74.5 degrees to -48.9 degrees C) for a single freeze (P <0.0005).
Conclusions: Uniform coagulative necrosis of human prostatic tissue in vivo can be accomplished throughout a significantly larger zone with a double freeze than with a single freeze. A double freeze at temperatures below approximately -40 degrees C results in necrosis. These findings provide a basis for more optimal use of temperature monitoring during cryosurgery, which is essential to ensure effective treatment of the entire prostate gland with minimum risk of damage to adjacent tissues such as the rectum and external sphincter.