23. When was extreme cold first used to treat prostate cancer?
The era of cryoablation of the prostate began in 1964. The freezing agent, liquid nitrogen, was delivered through probes that were inserted through the urethra into the prostate.1 (Figure 16)
Fig. 16
Fig. 16. This is a side view of the bladder, prostate, and urethra.
In 1972, Flocks made an incision in the skin and exposed the prostate.2 He then directly inserted freezing probes into the prostate. Again, liquid nitrogen was the freezing agent. These cancer patients experienced cure rates comparable to patients treated with radiotherapy and radical surgery. However, cryoablation did not become a widely accepted therapy because many cryo patients experienced post-operative voiding problems due to injury of the urethra, and a number of patients developed an opening between the urinary tube and the rectum (urethro-rectal fistula). 1. Gonder M, Soanes W, and Smith V. Experimental Prostate Cryosurgery. Invest Urol
1964; 14:610-9.
2. Flocks RH, Nelson CM, et al. Perineal Cryosurgery for Prostatic Carcinoma. Journal of Urology 1972; 108:933-5.
46
Bladder Prostate
24. What changes have been made in the past twenty years to improve the safety and effectiveness of cryoablation of the prostate?
Landmark advances in the cryoablative technique were made between 1990 and 2000. Liquid nitrogen was replaced by a combination of argon (freezing gas) and helium (warming gas) gases.1(Figure 17)
Fig. 17
Fig. 17. The two large tanks contain argon and helium. The gray probes to the left of the computer are closed circuits that circulate these gases. The computer provides continuous monitoring of the temperatures in and around the prostate.
Liquid nitrogen did not permit precise control of the targeted tissue because the area frozen continued to expand after the flow of nitrogen was stopped. With the two new gases, the area frozen was contained by shutting off the argon and turning on the warming gas, helium.
47 Cryo Probes
Temperature sensors were added to permit continuous real-time temperature measurements in and around the prostate. A rectal ultrasound probe was introduced to provide real-time images of ice formation in the prostate. (Figure 18)
Fig. 18
Fig. 18. This is an ultrasound image of the prostate. The white double U is the lowest edge of the ice. The white edge is continuously used to determine the amount of prostate that has been destroyed.
These images, in combination with temperature measurements provided by the temperature sensors, help the physician determine when the cryoablative procedure is complete, while protecting nearby critical tissue. (Figure 19)
Fig. 19
Fig. 19. The blue temperature-sensing probes to the external sphincter (ES), the anterior prostate (ANT or A), and Denonvilliers' fascia (DEN) surround the gray probes that carry argon and helium to and from the prostate. The monitor reports that cryo probes #1 and #2 are active and freezing 100% of each cycle. Probes #3-6 are inactive. The temperature in the external sphincter is 38°C or 100°F.
48
Rectal wall Ice edge
Finally, surgeons began warming the urethra, the urinary tube, during the procedure with a double lumen catheter. (Figures 20 and 21) This device minimized the chances that the urethra would be frozen during the cryo procedure.
Fig. 20 Fig. 21
Fig. 20. The warming tube has a central core that is surrounded by a thin plastic sheath. A warm solution (42 °C or 107°F) continuously circulates in the tube and protects the urethra from freezing. Fig. 21. This is the ultrasound image of the warming tube in the urethra.
Recent studies report that less than 0.5% of patients developed a fistula.
1. Saliken JC, Donnelly BJ, et al. The Evolution and State of Modern Technology for Prostate Cryosurgery. Urology 2002; 60:26-33.
25. Technical Details of the Total Cryoablation of the Prostate Procedure at the Penobscot Bay Medical Center
Preoperative evaluation includes serum PSA level, digital rectal exam, and trans-rectal guided twelve-core prostate biopsy with coincident determination of prostate volume. Hormonal therapy is instituted prior to Cryo therapy in patients with a prostate volume >50 ml. This therapy is not continued following the cryoablation. Bone scan, pelvic computed tomography, and laproscopic pelvic node sampling are performed in patients with high-risk prostate cancer to exclude metastatic disease.
Technique:
Cryoablation is performed using the Cryocare CS System (Endocare, Inc,. Irvine, CA). Argon and helium are the freezing and thawing agents. Multiple 2.4 mm cryoprobes (6 to 8) and 17- gauge thermocouples are placed under trans-rectal ultrasound (TRUS) guidance, utilizing the brachytherapy template. A urethral warming catheter containing a +42°C solution is placed prior to initiating the freeze. A double freeze/thaw cycle is performed under TRUS and thermocouple guidance. The target temperature throughout the prostate is -40°C. The argon freeze is initiated in the anterior probes and continued toward the rectum. In the anterior probes, freeze is present 100% of each cycle for at least 5 minutes and then lowered to 75%. In the lateral probes the
freeze time begins at 75% for each cycle. In the posterior probes, the freeze is active 25% of each cycle. The edge of the ice ball is carried down to the anterior rectal wall and out to the external sphincter. The temperature in Denovillier’s fascia is kept above -5°C. The sphincter temperature is kept above 20°C. Once the target temperature is achieved, a passive thaw is permitted for 3 minutes, followed by an active thaw with helium. The active thaw is discontinued once the prostatic architecture, the cryoprobes, and thermocouples are clearly identified. After the second freeze, again a passive thaw is permitted for 3 minutes, followed by an active thaw. Following the thaw, the urethral warming catheter is replaced by a 3-way #18F Foley. The patient is then transferred to the recovery room. See Addendum #6 on page 76 for an analysis of various cryosurgical techniques utilized in cryoablation of the prostate.