Cryosurgery or cryoablation is a recognized therapeutic option for prostate cancer. This chapter will deal primarily with whole gland ablation. Except for information pertaining to specific cryogenic machines or systems, the ensuing remarks apply in general to all cryoablative procedures for prostate cancer.
Mechanism of Action of Cryoablation
The cytotoxic action is based on induction of coagulative necrosis in the tissue exposed to very low subzero temperatures. Several factors are implicated in the lethal tissue injury from rapid freezing and slow thawing. These include direct mechanical disruptive damage to cellular and organelle membranes, biochemical derangement with pH changes, protein denaturation, electrolyte shifts and osmotic shock between intracellular and extracellular spaces, ischemia and hypoxia from micro-vascular thrombosis and neurovascular bundle damage, as well as possible antitumor immunologic actions from antigen release. The key to success for prostate cancer cryoablation is having good knowledge of the freeze killing zones of the iceballs, positioning the cryoprobes accurately in the target site, and avoiding damage to adjacent normal tissue.
Primary whole gland therapy can be performed for patients with clinical stage T1c to T3 disease, without evidence of metastatic disease, and regardless of tumor grade or hormonal response status. Patients should ideally have a life expectancy of 5–10 years. Men with comorbidities that would render surgery or radiotherapy more complicated or risky are still eligible. Those with large prostate volumes in excess of 50 mL may undergo neoadjuvant hormonal therapy for downsizing prior to cryoablation.
Absolute contraindications to whole gland prostate cryoablation include a history of urethrorectal fistula, extensive cancer involvement in the periurethral area, and prior trauma or surgery that may have resulted in distorted and unpredictable pelvic anatomy. Strong relative contraindications include previous abdominoperineal resections and severe rectal pathology such as rectal stenosis and radiation proctitis. Other relative contraindications include very large prostate glands in excess of 80–100 mL, significant obstructive urinary symptoms and prior extensive transurethral resection with a resultant large prostatic fossa defect.
For salvage cryoablation following localized failure of radiation therapy, histologic confirmation of local disease recurrence or persistence, as well as a negative metastatic workup, is mandatory. Serum prostate-specific antigen (PSA) levels exceeding10 ng/mL or a short PSA doubling time (under 6 months) strongly suggests metastatic disease and would be a contraindication for salvage cryoablation. Evidence of significant tissue damage from radiotherapy would also be a contraindication.
Different cryogenic systems deliver ice balls of different size and shapes. Although the current systems all use, based on the Joule-Thomson Principle, argon gas as the cooling source and helium as the rewarming (thawing) source, the number of the cryogenic probes or needles and schema of probe placement vary significantly. It is essential to become familiar with the specifications of the particular cryogenic system one is using for the procedure, in terms of iceball sizes and shapes.
The V-Probe Variable Ice Cryoprobe System (Endocare, HealthTronics Inc) ( Fig. 80.1 ) provides adjustable settings for various ablative ice lengths ranging from 1.5 to 5 cm, with different dimensions for various isotherms. Generally five or six such 2.4-mm probes are used ( Fig. 80.2, A , B ). It is of paramount importance to remember the iceballs visualized on intraoperative ultrasound do not correspond to the actual therapeutic cytocidal zone, which is predictably smaller. For instance, the 4-cm V-Probe can create an ice ball with maximum 39 mm diameter and 57 mm length. However, the dimensions of the –40°C zone are 21 mm in diameter and 40 mm in length. Also of great clinical significance are the corresponding measurements of the –20°C zone, respectively, 28 mm and 45 mm. Knowledge of these dimensions is important to ensure adequate treatment of the entire prostate while avoiding damage to adjacent organ or tissue.
The SeedNet CryoNeedle System (Galil Inc) uses 12–15 smaller-caliber (17-gauge) needle-shaped probes ( Fig. 80.3 ). These 1.47-mm “CryoNeedles” create smaller ice balls, or “IceSeeds.”
The –40°C-zone dimensions are 8 mm diameter and 17 mm length whereas the –20°C-zone dimensions are 14 mm diameter and 18 mm length. The 0° zones (ie, dimensions of iceballs seen on transrectal ultrasound) are 18 mm in diameter and 27 mm in length. “IceRods” are intended for larger and longer prostates, capable of creating bigger iceballs ( Fig. 80.3 ) (−40°C-zone dimensions are 14.5 mm diameter and 34 mm length; and 0°C-zone dimensions are 32 mm and 56 mm, respectively).
A good-quality biplanar transrectal ultrasound system is essential for adequate intraoperative anatomic visualization and delineation ( Fig. 80.4, A ). Software for three-dimensional ultrasound reconstruction is a useful option, for confirmation of probe positioning and for monitoring intraoperative iceball progression ( Fig. 80.4, B , C ). The ultrasound probe is supported by a cradle mounted to the operating table. A stepper mechanism with 1-cm increments controlling depth of probe insertion is preferred.
Template for probes and needles: A template and stand with a drilled matrix usually intended for brachytherapy, mounted on the ultrasound cradle, is commonly used to guide the CryoNeedle insertion ( Fig. 80.5 ), although some surgeons with the Endocare system prefer the “free-hand” technique.