Radiofrequency Ablation of Hepatic Lesions: A Review

Venkataramu N. Krishnamurthy, MD; V. Javier Casillas, MD; Lina Latorre, MD

Disclosures

Appl Radiol. 2003;32(10) 

In This Article

RF Devices

The U.S. Food and Drug Administration has approved RF devices manufactured by three companies--RITA Medical Systems (Mountain View, CA), Radiotherapeutics (Mountain View, CA), and Radionics (Burlington, MA)--for treatment of liver tumors that are not amenable to surgery ( Table 1 ).

For the model 70 or model 90 Starburst XL devices (RITA Medical Systems), the ablation protocols are based on the attainment of a target temperature in the tissue. To perform ablation, two grounding pads are applied to the thighs or back of the patient. The tip of the needle is advanced with the prongs retracted, to the desired location, and then the prongs are partially deployed. There is an automated program that will slowly raise the generator power from 25 W to peak within 1 to 1.5 minutes. Full deployment of the prongs is performed when the target temperature (usually 95°C to 105°C) is achieved. The device automatically adjusts the power to maintain the target temperature as the tumor is cooked. The ablation is carried out to a preselected time in the treatment protocol that is at least 10 minutes for smaller tumors and >20 minutes for tumors >5 cm in diameter. For satisfactory ablation, the company recommends that after completion of the ablation cycle, the temperature reading from the central electrode must be >50°C for at least 1 minute. The needle tract is ablated with a tract ablation program, which maintains the temperature >60°C while removing the needle.

The ablation protocols for the LeVeen needle electrode (Radiotherapeutics) are based on tissue impedance, unlike the target temperature used in the RITA devices. Two grounding pads are applied to the patient's thighs. The needle is inserted to the desired location, and the prongs are deployed to full length. The generator is initially set to 30 W and is then increased by 10 W steps every minute until the peak power of 90 W is attained. At this power, ablation is continued for 15 minutes or until the high impedance stops current flow. If the device did not impede out in the first 15 minutes, then the generator is switched off for 30 seconds and then restarted at maximum power and run until high impedance again stops further ablation or until 15 minutes has elapsed. If the ablation stops due to high impedance during the first cycle, the machine is switched off for 30 seconds and restarted at 70% of maximum power and run for 15 minutes or until high impedance again stops the ablation process.

The ablation protocols for the Cool-tip RF electrode (Radionics) are also based on tissue impedance. The needle shaft has two internal channels connected at the tip, allowing perfusion of chilled water. The internal cooling of the needle prevents desiccation and charring at the needle tip, allowing better dis-sipation of the frictional heat, which increases the size of the thermal injury.[23] Recently, a clustered three-needle electrode system has been introduced, which has three similar internally cooled needles arranged in a parallel, triangular manner and attached to a common hub. This arrangement is shown to produce a larger volume of ablation than a single-electrode system produces.[24]

Four grounding pads are applied on the patient's thighs. The single or cluster needle is inserted to the desired location and then connected to the generator and perfusion pump that circulates sterile chilled water. The automated program in the generator increases the power to a peak of 200 W within 1 minute. The power is maintained until the impedance rises more than 20 (omega), then the power is reduced to 10 W for 15 seconds. The power is increased once more to maximal power until the impedance rises again above 20 (omega). This cycle is repeated for a total of 12 minutes.

processing....