Current state of urological cryosurgery: prostate and kidney

Abstract

Prostate cancer continues to be the most prevalent cancer in American men and while the lifetime risk of mortality from the disease is ≈4%, we remain unable to identify which individuals actually harbour this risk. PSA measurements alone lack the sensitivity and specificity to identify men at risk for the disease, as well as in predicting organ-confined disease, yet it remains the best tool we have to date. Thus, we remain with the dilemma of who to biopsy, and if the biopsy is positive who to treat. To date, no study has shown oncological superiority for any type of curative therapy for localized prostate cancer and various options exist 1, which leads us to the initial focus of this article. What is the current state of cryosurgery for localized prostate cancer? The second focus regards the use of cryosurgery for management of localized RCC. One of the earliest descriptions of the application of cryosurgery to the prostate was in 1966 by Soanes et al.2. A liquid nitrogen-based system was used and therapeutic application to the prostate was monitored through open incisions or transurethrally under direct visualization for both benign and malignant disease. Limitations in the technology and limited ability to accurately place the cryoprobes and monitor the extent of freezing in real time were characteristics of the first-generation cryosurgical technique, which ultimately resulted in abandonment of the technique due to unacceptable complication rates 3, 4. Second-generation cryotherapy was introduced in the early 1990s and used TRUS imaging, which allowed for real-time monitoring of the extent of ice formation in the tissues 5, 6. This provided for more accurate cryoprobe placement and more thorough coverage of the prostate. Transperineal percutaneously introduced multiprobe cryosystems marked an improvement in the delivery of this technology, but procedure-related morbidity remained an issue 7. Limited cryosurgical experience continued, and technical problems revolved around poor control of the liquid nitrogen cooling agent, lack of an effective urethral warming device 8, 9 and inability to monitor target tissue temperatures. Subsequently, reports on the role of urethral warmers coupled with TRUS guidance represented a significant technological advancement, which enhanced delivery of this therapy with decreased procedure-related morbidity 10-12. Target tissue temperature monitoring in the form of thermocouple devices became available in the same period and provided the means to assess the achievement of lethal target tissue temperatures of −40 °C, which became the endpoint of the freezing cycle. Third-generation cryosurgical technology became available in 2000, employing delivery of pressurized argon gas and helium gas through small direct access transperineal probes, which functioned to deliver cooling and warming properties of the respective agents based on the Joule–Thompson effect. The Joule–Thompson effect is the means by which different gases undergo temperature changes upon depressurization in accordance with unique gas coefficient properties. Specifically, argon gas undergoes rapid cooling to – 185.7 °C upon depressurization from 20.68 MPa in the storage tank to 0.103 MPa at the tip of the enclosed cryoprobe. The expanded gas is then circulated back to the cryogenic machine through the larger outer lumen of the cryoprobe and attached supply hose to be vented out of the machine into the surrounding air. Conversely, helium gas warms to 67 °C upon depressurization to provide for active warming of the target tissues 13 and the historical procedure-related morbidity and complication rates were markedly reduced by these developments 11, 14, as well as by implementation of pinpoint-thermocouple devices that allowed for continuous monitoring of target tissue temperatures. Additional modifications were new computer software programs that provided the surgeon with intraoperative treatment planning and computer-assisted cryoprob