Prostate: Cryotherapy

Cryoablation

“The in situ freezing and devitalization of tissues, which can be applied and controlled precisely to produce a predictable zone of necrosis that will destroy the target lesion as well as an appropriate margin of surrounding tissue”

(Patel BC, et al. J Surg Oncology. 1996;63:256-264)

Cryobiology

As temperatures approach the hypothermic range, extracellular water begins to crystallize and a hyperosmotic extracellular environment that draws water out of the cells is created. As the process continues, extracellular ice crystals grow, cells shrink, and membranes and cell constituents are severely damaged. Within a short time (minutes), the increased electrolyte concentration is sufficient to destroy the cells. This effect of cell dehydration and solution concentration, called solution-effect injury (Figure 1), is not always lethal to cells; intracellular ice formation (Figure 2) is a more significant threat to cell viability and is almost always lethal (Mazur, 1963, 1968, 1977, 1981; Maryman, 1966; Pegg, 1987; Sherman, 1962). Solution-effect injury is associated with low freezing rates, while intracellular ice formation is commonly associated with fast freezing rates. Although pure water begins to freeze at 0°C, extracellular ice formation is initiated at approximately –7 to -10°C, and by -15°C intracellular ice begins to form (heterogeneous nucleation). By -40°C all metabolic processes are expected to have ceased (homogenous nucleation) (Baust and Change, 1995). Either an extremely low freezing rate (on the order of several degrees Centigrade per minute) or a very rapid freezing rate (on the order of hundreds of degrees Centigrade per minute) is considered to have the most destructive effect on biological tissue.

Figure 1: Solution-effect injury
Normal Tissue	Extracellular ice formation	Hyperosmosis & Dehydration
Figure 2: Intracellular ice formation
Normal Tissue	Intracellular ice formation	Intracellular ice crystals

Applying cold energy to human tissues is a well-known technique for treating various lesions as an alternative to surgery. Since the 19th Century, many trials have been conducted to prove its efficiency in tissue ablation. In the early 1960’s cryosurgery was revived with two types of equipment that utilized liquid nitrogen as the cryogen. The first generation devices used a funnel through which liquid nitrogen was poured. Large diameter probes subsequently replaced them. Due to difficulties in controlling the size of the iceball and its freezing-thawing characteristics, this equipment was suitable only for clinical applications that did not require a high degree of accuracy. It was abandoned due to the high rate of significant complications and adverse effects.

In the late 1990’s the SeedNet™ Cryotherapy System was introduced, a new generation cryotherapy system based on an advanced gas expansion method (Joule-Thomson principle). This method demonstrates significant improvement in controlling the freezing process, and through use of ultra-thin CryoNeedles™ ensures that the target tissue is thoroughly frozen without gaps in the frozen region (high resolution coverage).