The technique used at our institution is a modification of the one originally described by Onik and colleagues [10] and incorporates the advances reported from our center [11,12]. In our initial experience, patients were treated by a team consisting of a urologist and a radiologist. Currently, most treatments are carried out by a urologist proficient in the use of ultrasound equipment. Prostate cryoab-lation is usually an in-patient procedure requiring an overnight stay in the hospital, but it may be carried out as an out-patient procedure with same-day discharge. Intravenous antibiotics (cefazolin, gentamicin, and metronidazole) are administered 1 hour preoperatively. The rectum is emptied by repeated use of a fleet enema. The vast majority of patients are treated under spinal anesthetic. The patient is placed in the lithotomy position, and sequential compression devices are applied to the legs preoperatively. Patient positioning is important for providing good access to the perineum, especially if one is using a brachyther-apy arm and a computer treatment-planning system. A low lithotomy position is used. The patient's perineum is placed level with the end of the operating table to allow unimpeded access. If the pubic arch is low, an exaggerated lithotomy position can be used to improve transperineal access to the prostate gland. The entire perineum and suprapubic area is prepped with provadone iodine solution, and the patient is draped as for an endoscopic procedure.

A flexible cystoscope is used to visualize the prostate and bladder, to fill the bladder, and to guide the placement of the suprapubic 10 French pigtail catheter. We prefer a suprapubic to a urethral catheter, because we feel that this is easier for the patient, and it avoids irritation of the urethra and prostate during the recovery period. The catheter is removed once the patient's postvoiding residual urine is consistently below 100 ml, typically around 2 weeks postsurgery. Next, a guidewire is inserted into the bladder through the cystoscope, and the cystoscope is removed. A well-lubricated urethral warming catheter (Endocare, Irvine, CA, USA) is introduced through the urethra over the guidewire. The guidewire is removed, and the urethral warming catheter is left in the patient throughout the treatment and for 30min afterward.Water at 39.5°C is circulated through the warming catheter using a warmer pump system, circulating at a rate of 400 to 500 ml per minute. We routinely add methylene blue dye to this circulating water to aid in rapid identification of any leaks. Some operators initially insert a Foley catheter, replacing it with the warming catheter once the cryo-probes are in place, thereby reducing the risk of puncturing the warming catheter during cryoprobe insertion. A biplane TRUS probe (Aloka, Tokyo, Japan) is inserted into the rectum to visualize and measure the prostate. Intermittent instillation of water into the rectum facilitates good visualization of the prostate. This also distends the rectum to eliminate wrinkles in the anterior rectal wall, which can falsely exaggerate the thickness of the rectal wall.

Six cryoprobes are routinely used, although the number can vary if the prostate is very large, small, or unusually shaped. We refer to the probes by a standard numbering system, which we use in every case (Fig. 1). This system is used because probes are operated sequentially from anterior to posterior, i.e., probes 1 and 2 are operated first, followed by 3 and 4, and then 5 and 6, working from anterior to posterior. This sequencing is utilized to maximize the TRUS visualization during the procedure. If the operator is using 3-mm cryoprobes, probe placement is greatly facilitated by using a rapid access needle/dilator/sheath (Fasttrac, Endocare). This method replaces the original Seldinger technique and significantly reduces the operating time. When the smaller sharp cryoprobes (2.4,1.8, and 1 mm) are used, they are introduced per-cutaneously directly into the gland under TRUS visualization. The two anterior sheaths (1 and 2) are initially placed as demonstrated in Fig. 1. The cryoprobes must be less than 10 mm from the edge of the gland to ensure adequate freezing of the periphery. The temperature between the probes will fall more rapidly than the temperature at the edge of the iceball. Anterior cryoprobes can be placed up to 3 cm apart if necessary, whereas all other cryoprobes should be separated by no more than 2 cm (Fig. 1). Sagittal TRUS scanning is used to confirm spatial separation of the cryoprobes, and coronal plane scanning is used to ensure proper positioning of the cryoprobe tip at the base of the prostate. Once in place, the probes are "stuck" while the remaining probes are inserted. "Sticking" refers to lowering the temperature of the probes to -10°C, which results in the cryo-

Right Neurovascular Bundle Prostate
Fig. 1. Cryoprobe placement template. RNVB, right neurovascular bundle; LVNB, left neurovascular bundle

probe's becoming frozen in place without growing a large iceball. The posterolateral probes (3 and 4) are placed next. Since the prostate resembles an inverted cone, the probes can be directed laterally from the apex to the base while being inserted, to match the shape of the gland. These must be less than 10 mm from the periphery of the gland. There should be no more than 20 mm between probes 1 and 3 and between probes 2 and 4 to ensure adequate freezing between the probes (Fig. 1). The posteromedial probes (5 and 6) are placed last. Because this placement approaches the warmer, we typically use the coronal plane on the ultrasound probe to place these probes, with the transverse view to fine-tune positioning and ensure adequate separation between cryoprobes. These probes can also be directed laterally when moving from the apex of the gland towards the base, to conform to the shape of the prostate. The iceball generated on these probes is closest to the rectum, and its growth will often dictate the end of the freeze. It is important, therefore, that these probes be placed far enough away from the rectal wall.When the cryoprobes are oriented in the coronal plane, they are placed no more than 2 cm apart, closer to the midline than to the posterior margin of the gland. This ensures good freezing across the midline before the iceball reaches the rectal wall.

In placing the probes, lateral placement is very important, because the temperature between the probes is much lower than the temperature at the edge of the iceball. We are always mindful of achieving sufficiently cold temperatures around the gland margin, especially adjacent to the neurovascular bundles where the blood flow is most concentrated.

Thermocouples are a critical part of the cryosurgical procedure, because ultrasound alone is unreliable in ensuring adequate freezing. A minimum of three and as many as five thermocouples can be placed around the gland: one in each neurovascular bundle (Fig. 1), and one at the gland apex in the midline, just anterior to the rectal wall. This is an area that is prone to inadequate freezing and is well documented as an area of high risk for a positive margin. Other thermocouples can be placed anterior to the gland or at any point where specific temperatures need to be achieved. Many cryosurgeons also place a thermocouple in the external sphincter to monitor the temperature in this area. Before initiating the freeze, 30 to 50 ml of sterile saline is injected into the space between the anterior rectal wall and the posterior surface of the prostate to separate the two structures. This is a very important step, which greatly facilitates an aggressive freeze in the posterior gland without endangering the rectum. The saline causes good separation and also appears to induce hyperthermia and edema (Fig. 2), even though some of the saline is dispersed during treatment. This practice facilitates a more prolonged freeze posteriorly and at a slower rate, thereby "sculpting" the iceball to the shape of the anterior rectal wall. The freeze is initiated with the two anterior probes. The posterolateral cryoprobes (3 and 4) are turned on when the initial iceball reaches these probes and the iceballs begin to coalesce anterior to the urethra. The anterior probes are operated for at least 2min before probes 3 and 4 are turned on. It is best to begin the freeze slowly, using 50% of the maximum setting for this initial 2-minute period. The rate of freezing is then increased to 75% or 100%. The posteromedial probes (5 and 6) are turned on last. We initially run these probes at 25% and modify the posterolateral probes

Fig. 2. Ultrasound image of saline injected into the Denonvilliers fascia to increase the separation between the prostate and the posterior rectal wall

(3 and 4) at the same time. The temperature of probes 3 and 4 determines the speed of iceball development on probes 5 and 6. This is the critical part of the procedure, and it is better to proceed slowly, allowing the iceball to grow slowly and therefore conform to the shape of the gland and the anterior rectal wall. The operator should anticipate that when ice bridges across the posterior prostate between the urethra and the rectum, the temperature and behavior of this ice directly anterior to the mid-rectum are influenced by cryoprobes 3 and 4 as well as probes 5 and 6.

At all times, but especially during this part of the procedure, the iceball must be monitored closely to ensure adequate freezing and to protect the anterior rectal wall. The thermocouples are very important, because they relay temperature information much more accurately than the appearance of the iceball. As the iceball approaches the rectal wall, intermittent digital rectal examination (DRE) is a very useful adjunct to TRUS, allowing the surgeon to palpate the anterior rectal wall. It is important to ensure that the mucosa feels soft over the hard iceball lying underneath. On many occasions, TRUS has misled us into believing that there was a very large margin of safety, when DRE revealed the rectum to be very thin but redundantly folded on itself. There will be occasions when the iceball will extend posteriorly to the rectum before the apical thermocouple reaches at least -20°C. In these cases, the edematous reaction to the first freeze will facilitate a more aggressive freeze on the second cycle. Finally, it has been our experience that the operator should continue the freeze longer than he or she might think necessary in order to achieve a truly adequate freeze. As long as the rectum is safe, the operator should strive to achieve an iceball that becomes distinctly flat or even concave to palpation on DRE as it begins to extend laterally around the rectum. Once the first cycle is complete, the argon (the freezing agent) is turned off until the entire prostate is thawed and no ice is visible on ultrasound. Helium (thawing agent) is circulated through the probes to accelerate thawing. This can take between 10 and 30min, depending on blood flow to the prostate. Before starting the second freeze, it is important to check that none of the cryoprobes have slipped or require repositioning. The second freeze is executed in the same manner as the first. The second freeze consistently progresses faster than the first because of diminished thermal capacity in the previously frozen tissue.

As described above, there are three fundamental steps involved in performing prostate cryoablation. First, a cryoprobe and thermocouple placement strategy is determined. Second, the cryoprobes and thermocouples are placed in the prostate. Finally, the prostate is frozen twice with an interposing complete thaw. Commercially available treatment-planning software, as well as freezing algorithms that control cryoprobe operation based on thermocouple feedback, are now available and greatly facilitate the procedure by aiding in each of these three steps.

Optimization of probe placement is accomplished by capturing an ultrasound image of the prostate. The planning software uses the geometry of the prostate, urethra, and rectal wall to calculate the optimal positions of the cryoprobes and thermocouples. Probes are then inserted through a brachytherapy-like template placed at the perineum. Once this is done, the cryomachine is started in an auto-freeze mode. With the use of real-time temperature feedback from the thermocouples, the freezing protocol, as described above, is performed, and the flow of argon and helium through the cryoprobes is controlled by the computer.

On completion of the procedure, the cryoprobes are thawed and withdrawn. The urethral warming catheter is left in place for 30min after the procedure to protect the urethral mucosa against latent freezing and is then withdrawn in the recovery room. Patients at our institution are admitted overnight and discharged the following morning. Many centers perform cryoablation as an outpatient procedure.

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