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material

material and methods
  • Sterile drapes, towels
  • 22-gauge needle for anesthesia, scalpel
  • Iodine, 1% lidocaine
  • CT scan (Volume Zoom siemens®) and / or Sonography
  • Radio Frequency device (Berchtold®) and needle

 

RADIO FREQUENCY DEVICES:

For adequate destruction of tumor tissue, the entire volume of a lesion must be subjected to cytotoxic temperatures. Hence, effective heating throughout the target volume (i.e., the tumor and 5- to 10-mm thickness of normal tissue) is required. Thus, an essential objective of ablative therapy is achievement and maintenance of a 50°-100°C temperature throughout the entire target volume for at least 4-6 minutes. However, the relatively slow thermal conduction from the electrode surface through the tissues increases the duration of application to 10-30 minutes. Tissues cannot be heated to greater than 100°-110°C without vaporizing, and this process produces significant gas that both serves as an insulator and retards the ability to effectively establish a radio-frequency field. The vaporization or carbonization around the electrode tip can also retard heat conduction within the tissue, often in an asymmetric fashion. This process coupled with the rapid decrease in heating at a distance from the electrode essentially limits the extent of induced coagulation to no greater than 1.6 cm in diameter. Many investigators have explored and several corporations have manufactured new radio-frequency ablation devices based on technologic advances that increase heating efficacy. To accomplish this increase, the radio-frequency output of all commercially available generators has been increased to more than 150 watts, which may potentially increase the intensity of the radio-frequency current deposited at the tissue. Expandable electrodes permit the deposition of this energy over a larger volume. In addition, this design decreases the distance between the tissue and the electrode, thereby ensuring more uniform heating that relies less on heat conduction over a large distance. Alternate strategies to increase the energy deposited from a single radio-frequency electrode have also been developed. The internally cooled electrode design minimizes carbonization and gas formation around the needle tip by eliminating excess heat near the electrode. The removal of this heat by a "heat-sink" effect of flowing fluid in the electrode permits increased energy deposition and deeper tissue heating. Preferential cooling of the tissues near the electrode allows heating of tissues farther from the electrode when high radio-frequency current is being applied. A combined approach that involves use of a multiprobe cluster of internally cooled electrodes with pulsing has also been described with the claim of even greater coagulation than that achieved by any of the individual methods alone. Viewed in total, these technologic developments can be used to create an ablation lesion with a maximum diameter of 5.0 cm. We are using a new commercially available device using a single probe system with continuous infusion of saline without exceeding a 110°C maximum temperature threshold (60W, Berchtold®/ Germany). The continuous infusion of saline at the tip of the needle allows to increase heat and electrical conductivity. The Berchtold® radio frequency device relies on an electrical measurement of tissue impedance to determine that tissue boiling is taking place. The impedance rises can be detected by the generator, which can then reduce the current output and increase the saline flow. Injection of NaCl solution during RF ablation can increase energy deposition, tissue heating, and induced coagulation. Radio-frequency ablation is limited, however. With currently available devices, the largest focus of necrosis that can be induced with a single application is approximately 4-5 cm in greatest diameter. Thus, the diameter of suitable lesions must be less than 3-4 cm. Other limitations are the proximity of the tumors to large vessels, which may prevent adequate heating, as well as proximity to central bile ducts, which predisposes the patient to a risk of biliary complications. Finally, treatment of superficially located tumors carries a risk of injury to adjacent organs.