Radiofrequency ablation therapy (RFA) is considered to be a reliable alternative to surgical resection for patients with primary and metastatic liver tumors. RFA delivers energy into the tumor through non-insulated needle electrode tips, causing a high-frequency alternating current to flow and resulting in coagulation necrosis of the tumor tissue. Compared to percutaneous ethanol injection (PEI) and microwave coagulation therapy (MCT), RFA can induce a larger and more predictable area of coagulation necrosis. Therefore, this technique may reduce the number of required treatment sessions and shorten the hospital stay. Three different RFA devices are presently available, and their usefulness has been compared. Representative adverse effects of RFA include local pain, intra-abdominal bleeding, pleural complications, and needle tract seeding. Although more studies are required to precisely define the indications and to estimate the long-term effects, RFA is expected to become a major therapeutic technique for the treatment of primary and metastatic liver tumors.

View full abstract

Since radiofrequency ablation (RFA) therapy for liver tumor was established, it became a standard percutaneous therapy. However, after the first ablation microbubbles sometimes obstruct a clear observation of the tumor under ultrasound guidance, and despite multiple RFA, a part of the tumor may remain viable. To solve this problem we developed a computer-guided navigation system for an accurate electrode insertion. We used POLARIS^TM (Northern Digital Inc., Ontario, Canada) as the active optical tracking system. The POLARIS^TM allows us to determine the real time 3D positions of active markers. With this system we could determine the location and the direction of the RFA electrode and the distance from the tip of the electrode to the target, which were displayed on the PC monitor. We also investigated the accuracy of this system as a preliminary test for its clinical application. The primary error between the real and the theoretical target was 2.88mm. The first insertion error was 5.78±1.97mm and the second insertion error was 8.01±1.01mm. While some hardware improvements and more technical experience are needed for its clinical applications, this computer-guided navigation system will be of great help for an accurate electrode insertion, especially in case of unresectable liver tumors subjected to RFA.

View full abstract

Aim
Based on our experiences of treating hepatocellular carcinomas (HCC), we discuss some of the techniques that are required in order to gain appropriate outcomes. We also report the clinical significance of different radiofrequency devices.
Methods
One hundred and forty-seven cases with HCC were treated using radiofrequency ablation. Either a percutaneous approach or a laparoscopic approach was selected depending on the location and the size of tumors. A guiding needle technique was routinely applied to the percutaneous approach in order to make it safer and easier to target the tumor. Laparoscopy under general anesthesia was assisted by the ultrasound guidance to locate the tumor.
Two different radiofrequency devices : an expandable electrode with a thermo-controlled generator (Model 30, RITA) and a cool-tip electrode with an impedance-controlled generator (Cooltip-system, Radionics) were compared. The clinical advantages of both devices were assessed.
Results
Of the 94 cases that were treated by RFA as the initial treatment for the tumor, 50 were bearing a single nodule smaller than 30mm. After RFA, most cases of this group were diagnosed as completed ablation, and there were three cases (6%) with local recurrences.
A guiding needle technique was applied to all the percutaneous approaches which not only enabled us to target the tumor precisely, but also offered a safe route for biopsy and hematostatic procedure. For the laparoscopic approach, the ultrasonic guidance was essential when the tumor was located under the liver surface.
Compared to the expandable electrode, the use of the cool-tip electrode resulted in the reduction of the number of punctures by half, thus shortening the operation time by half. This difference may be attributed to the difference in the capacity of the generator power.
Conclusions
Radiofrequency ablation may play a major role in treating hepatocellular carcinoma provided the techniques and procedures are adequate.

View full abstract

Characteristics of particulate heating mediators in radiofrequency (RF) capacitive hyperthermia were investigated. Four ferromagnetic ferrite particles (Cu (II) Fe (III)₂O₃, Mg (II) Fe (III)₂O₃, Mn (II) Fe (III)₂O₃, and Ni (II) Fe (III)₂O₃) in addition to magnetite particles and other non-ferromagnetic metal oxide particles (α-Fe₂O₃, α-Alumina, Ag (II) O, and ZnO) were tested using 8 MHz RF heating device. As a result, ferromagnetic particles could generate heat specifically in RF capacitive, but non-ferromagnetic particles could not. In addition, dispersiblity of particles was an important parameter for heat generation. Temperature increase of Mg (II) Fe (III)₂O₃ was well improved by sonication. It was shown that alternative magnetic field is generated around ferromagnetic particles in 8 MHz RF electric field and that heat is generated in ferromagnetic particles due to hysteresis loss by the action of alternative magnetic field ; i. e. the same heat generation mechanism with inductive heating.

View full abstract