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EDUCATION EXHIBIT |
Department of Radiology, Stanford University Hospital, Stanford, California
Surgical resection of primary and metastatic liver tumors is considered to be the only potentially curative treatment of these common malignancies, with expected 5-year survival of 25%–30% for hepatocellular carcinoma and 30%–40% for colorectal metastases (1–3). However, open surgical procedures are often limited by the extent of tumor involvement or poor hepatic reserve, making most patients ineligible for resection. Furthermore, despite the improved survival over that of systemic chemotherapy, surgical resection has been associated with a perioperative mortality of up to 10% (4). Thus, minimally invasive image-guided treatment strategies such as transcatheter arterial chemoembolization and percutaneous interstitial ablation have been widely applied to hepatic malignancies over the past 2 decades. Regional image-guided therapy has the advantage of producing local tissue destruction or achieving high tumor drug concentrations with few systemic side effects. Refinement of previously established methods and development of newer technologies in the interventional arena have allowed extension of these techniques into other areas such as gynecologic, genitourinary, and lung malignancies (5–8).
Recently, the investigations of novel approaches involving thermal ablative techniques for tumor destruction have intensified. These include the use of RF, microwave, laser, and high-intensity focused US ablation. Of these, RF ablation is the most widely studied and has quickly become a leading method of interstitial tumor ablation owing to its availability, ease of use, and effectiveness of treatment.
RF ablation is a method for deposition of thermal energy in tissue. Radio-frequency current is delivered through a needlelike electrode, and local ionic agitation converts the electrical energy into heat. The generated heat is conducted to adjacent tissues, causing protein denaturation and cell death. However, higher power settings can cause desiccation and charring of adjacent tissues, preventing further heat generation and conduction. In comparison with the earlier generation of devices, the current RF ablation equipment uses a combination of needle designs, generators, and algorithms that can create bigger lesions by encompassing large volumes and minimizing tissue charring. As such, the modern RF tools are also capable of causing significant injury to normal tissues adjacent to targeted areas.
In RF ablation of malignancies, as with any other method of cancer treatment, the therapeutic index of the treatment as judged by its risks versus benefits must be carefully considered. To that end, physicians performing the procedure should have full knowledge of benefits and potential complications of RF ablation. In the absence of any prospective multicenter trials to assess the comparative outcome, retrospective multicenter analyses such as the Italian Multicenter Cooled-Tip RF Study Group (9) and the Korean Study Group of Radiofrequency Ablation (10) can be sources of information to identify the at-risk patients and determine their suitability for RF ablation.
The preceding article by Rhim et al (10) addresses an important issue in RF treatment of primary and metastatic hepatic malignancies. This is an analysis of potential complications of hepatic RF ablation with nicely demonstrated examples of findings at imaging. Mechanisms likely responsible for the occurrence of each complication are discussed, which will serve as useful tools for the prevention and treatment of such.
Review of the literature reveals that the most common serious complications include infection, bleeding, liver failure in cirrhotic patients, and biliary injuries. Procedure-related death and tumor seeding are fortunately uncommon, occurring in less than 1% of cases. As pointed out by Rhim et al (10), perhaps the most important factor in preventing such complications is appropriate patient selection. Helpful steps include correction of coagulopathy to reduce the risk of bleeding and avoidance of large hilar tumors as much as possible to diminish the likelihood of central bile duct injury. Difficult-to-localize lesions (eg, at the dome) and those adjacent to critical structures (eg, colon, heart) should be considered for open surgical or laparoscopic RF ablation. A safer percutaneous approach to these locations awaits the development and validation of instruments for real-time monitoring to ensure adequate tumor necrosis while avoiding injury to adjacent structures. The hepatic functional reserve should also be considered prior to ablation to assess the potential for irreversible liver injury.
Although the report of the Korean Study Group of Radiofrequency Ablation (10) has all the weaknesses inherent to such retrospective surveys, many other groups have observed similarly low complication rates. In the initial results of the Italian Multicenter Cooled-Tip RF Study Group reported at the annual meeting of the Radiological Society of North America, the mortality and major complication rates were 0.11% and 1.52%, respectively (9). As in the report by Rhim et al (10), the most common postprocedure problems were bleeding and abscess formation, which accounted for 41% of the total complications. Solbiati et al (11) reported only two complications among 117 patients treated for colorectal metastases to the liver, confirming the safety of the percutaneous approach. However, most studies of relatively large numbers of patients performed to date have consisted of cases treated both percutaneously and surgically. Curley et al (12) observed a complication rate of 12.7% among 110 patients with hepatocellular carcinoma, which included bleeding, pleural effusion, and infection. In a study of 123 patients that involved ablation of tumors up to 15 cm in diameter, Iannitti et al (13) observed a morbidity rate of 7.1%.
Any discussion of complications of RF ablation would be of limited value in the absence of the corresponding efficacy data. Complications should be judged in the context of efficacy to better determine the therapeutic index of the procedure, which will determine the suitability of any patient for RF ablation. The Korean Study Group of Radiofrequency Ablation survey does not include any data on local tumor recurrence, appearance of new lesions, or survival of the patients in their study (10). To that end, the reader must rely on other reports to judge the benefits of hepatic RF ablation.
As with complications, the reported efficacy of RF ablation is variable and dependent on the operator’s experience, method of localization, and choice of equipment. Patient factors influencing the outcome include liver function and presence of comorbidities such as severe coagulopathy. Other potentially important determinants of outcome include the pathologic features, stage, size, location, and number of tumors. Although none of these variables have undergone rigorous independent study, most authors agree that there is a correlation between these factors and the success of RF ablation.
It has been theorized that more uniform and complete tumor necrosis is achieved in hepatocellular carcinoma as compared with metastases, necessitating a more aggressive ablative approach to the latter (14). This is due to a more common prevalence of local tumor infiltration of the surrounding hepatic parenchyma by the metastatic foci. Complete margin-free destruction of tumors would therefore necessitate a more aggressive ablative approach, which may be associated with a higher rate of complications. However, the Korean Study Group of Radiofrequency Ablation survey found no significant difference in RF-related morbidity between primary and secondary hepatic malignancies (10).
Rhim et al (10) make the appropriate point that hepatic RF ablation is a safe procedure but that the complications are not negligible. The more widespread application of RF in tumor ablation has been hampered not by its associated complications but by the lack of prospective multicenter trials demonstrating a survival benefit. However, the future of this technology is bright. Overall, owing to the minimally invasive nature of RF ablation, low complication rate, and short hospital stay, the patients’ quality of life is maintained, leading to high acceptability. This together with the increasing evidence of the efficacy of RF ablation makes this approach a viable alternative in selected patients with hepatic malignancies. There are ongoing and planned prospective studies in this area, which will further elucidate the role of RF ablation in patients with hepatic malignancy.
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