Percutaneous cryoablation in cancer patients.

Unlike radiofrequency, microwave, and laser, cryoablation is a freeze-ablation method that does not heat the tissue. In cryoablation, high pressure Argon gas or liquid nitrogen is passed through a thin channel in the cryo needle and released at its tip. A sudden drop in the pressure of the argon gas creates a cooling of minus 40-140 degrees in the tissue. As a result of this phenomenon, which is called the Joule-Thompson effect, an ice ball is formed around the cryoablation needle. This ice ball causes the formation of ice crystals in the tumor, obstruction of the arteries and apoptosis resulting in widespread tissue death.

Cryoablation is a method used in medicine for the elimination of heart rhythm disorders, treatment of some dermatological disorders and in the treatment of severe cancer pain. However, the most common area of use is the freezing of tumors. Cryoablation was first used in the treatment of prostate and kidney tumors and was limited to this area for many years. The reasons for this may be unavailability of thinner cryoablation needles at that time, the use of liquid nitrogen instead of argon gas in the cooling and the lack of sufficient experience in physicians. However, cryoablation has been reinvented by the use of Argon gas in cooling in the 2000s and by producing very fine (17 gauge) needles suitable for percutaneous treatment. New generation cryoablation was first used by interventional radiologists in liver tumors. Although the results were quite good, cryoablation was not very popular in liver tumors because of successful and cheaper methods such as radiofrequency and microwave in the liver. In subsequent years, cryoablation has been widely used in lung, kidney, muscle, bone, breast, soft tissue and pancreatic tumors.

Needles placed in the tumor in cryoablation are called "probes" or "cryoprobes", as in the radiofrequency. Cryoprobes are straight needles and, as mentioned above, there is a thinner channel through which high pressure Argon gas passes. The ablation area in the cryoablation ranges from 2-3cm depending on the type of needle and is slightly smaller than radiofrequency and microwave. However, by increasing the number of needles, the ablation area can be enlarged and changed. For example, when the single needle is used, the ablation diameter is about 2 cm, whereas when 4 needles are used, it reaches almost 5cm, so it is possible to treat large tumors. Currently 25 cryoprobes can be used simultaneously in some cryoablation devices and percutaneous ablation can be performed in very large tumors. Cryoablation can be performed under local anesthesia because of the natural pain reducing effect of the cold. For tumors smaller than one cm, a single needle may be sufficient, and in larger tumors more than one needle should be used. These needles are typically placed into the tumor under ultrasound or tomography guidance. The iceball formed during the cryoablation can also be easily seen on ultrasound, computed tomography and MRI.

Thus, it can be understood immediately if the ablation area completely covers the tumor. While the temperature on the outer edge of the iceball is 0 degrees, it reaches minus 140 degrees in the center. In order for the ablation to be guaranteed, it is desirable that the iceball exceeds the tumor edges at least several milimeters during the procedure. During cryoablation, a 10 minutes freezing, 10 minutes thawing and 10 minutes second freezing protocol is usually administered, hence the ablation period lasts up to half an hour.

Cryoablation has some important advantages over other thermal ablation methods such as radiofrequency and microwave. First, cryoablation is a practically painless procedure because of the natural pain-relieving feature of the cold. Therefore, it can be performed under local anesthesia. This is important in patients in whom anesthesia is risky and when the patient should be awake during ablation. Since the nerves around the tumor die during cryoablation, postoperative pain is also less than that of radiofrequency and microwave. Second, while in radiofrequency and microwave the ablation area is usually less than 3cm, it can be much larger in cryoablation; If a sufficient number of probes are used, tumors up to 7-8cm in diameter can be easily treated, although in this case, the cost will also be increased. Third, unlike the other ablation methods that do not show the ablation area during the procedure, cryoablation can be monitored on ultrasound, CT and MRI, since the iceball can be readily seen with these imaging modalities. Thus, it can be realized whether the ablation is sufficient or not, and if it is insufficient, additional needles may be inserted or the ablation period may be prolonged. And fourth, cryoablation causes less damage to connective tissue (collagen tissue) than other ablation methods. Therefore, the possibility of damage to critical tissues or organs adjacent to the tumor may be reduced.

Besides these advantages, cryoablation has two limitations. First, the ablation time is longer, and second it is more expensive. The cost can be increased, especially in cases where a large number of cryoprobes should be used.