Small Hepatocellular Carcinoma: Comparison of Radio-frequency Ablation and Percutaneous Microwave Coagulation Therapy 1

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1 Vascular and Interventional Radiology Toshiya Shibata, MD Yuji Iimuro, MD Yuzo Yamamoto, MD Yoji Maetani, MD Fumie Ametani, MD Kyo Itoh, MD Junji Konishi, MD Index terms: Liver, CT, , , , , Liver neoplasms, , Liver neoplasms, therapy, Microwaves, Radiofrequency (RF) ablation, Published online before print /radiol Radiology 2002; 223: Abbreviations: HCC hepatocellular carcinoma PMC percutaneous microwave coagulation RF radio frequency 1 From the Departments of Diagnostic Imaging and Nuclear Medicine (T.S., Y.M., F.A., K.I., J.K.) and Gastroenterological Surgery (Y.I., Y.Y.), Kyoto University Graduate School of Medicine, 54-Kawaharacho, Shogoin, Sakyoku, Kyoto , Japan. Received April 16, 2001; revision requested May 11; revision received July 24; accepted September 7. Address correspondence to T.S. ( ksj@kuhp.kyoto -u.ac.jp). RSNA, 2002 See also the editorial by Goldberg in this issue. Author contributions: Guarantors of integrity of entire study, all authors; study concepts and design, T.S., Y.I., Y.Y.; literature research, T.S., Y.M., F.A.; clinical studies, T.S., Y.Y., Y.I., Y.M., K.I.; data acquisition, all authors; data analysis/interpretation, T.S., Y.I., Y.Y.; statistical analysis, T.S., Y.M., F.A.; manuscript preparation, T.S.; manuscript definition of intellectual content, T.S., Y.M., F.A., K.I.; manuscript editing, T.S., K.I., J.K.; manuscript revision/review and final version approval, all authors. Small Hepatocellular Carcinoma: Comparison of Radio-frequency Ablation and Percutaneous Microwave Coagulation Therapy 1 PURPOSE: To evaluate the effectiveness of radio-frequency (RF) ablation and percutaneous microwave coagulation (PMC) for treatment of hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Seventy-two patients with 94 HCC nodules were randomly assigned to RF ablation and PMC groups. Thirty-six patients with 48 nodules were treated with RF ablation, and 36 patients with 46 nodules were treated with PMC. Therapeutic effect, residual foci of untreated disease, and complications of RF ablation and PMC were prospectively evaluated with statistical analyses. RESULTS: The number of treatment sessions per nodule was significantly lower in the RF ablation group than in the PMC group (1.1 vs 2.4; P.001). Complete therapeutic effect was achieved in 46 (96%) of 48 nodules treated with RF ablation and in 41 (89%) of 46 nodules treated with PMC (P.26). Major complications occurred in one patient treated with RF ablation and in four patients treated with PMC (P.36). During follow-up (range, 6 27 months), residual foci of untreated disease were seen in four of 48 nodules treated with RF ablation and in eight of 46 nodules treated with PMC. No significant difference in rates of residual foci of untreated disease was noted (P.20, log-rank test). CONCLUSION: RF ablation and PMC thus far have had equivalent therapeutic effects, complication rates, and rates of residual foci of untreated disease. However, RF tumor ablation can be achieved with fewer sessions. RSNA, 2002 Hepatocellular carcinoma (HCC) is one of the most common malignancies in Far East Asia and Southeast Asia (1). Surgical resection can be a curative treatment for HCC. However, this cancer is usually associated with liver cirrhosis or chronic hepatitis, so most patients with HCC are not candidates for surgical resection owing to poor hepatic reserve. Several minimally invasive ablation techniques, such as percutaneous ethanol injection, percutaneous microwave coagulation (PMC), radio-frequency (RF) ablation, interstitial laser photocoagulation, and percutaneous acetic acid injection, have been used to treat HCC and metastatic liver tumors (2 19). Percutaneous ethanol injection is the most widely performed local treatment for small HCCs (2 4). The prognosis of patients with HCCs less than or equal to 3 cm in diameter who are treated with percutaneous ethanol injection is comparable to that of patients who are treated with surgical resection (3,4). Several reports from Europe and the United States, however, have indicated that RF ablation is very effective for the local control of small HCCs (5,9 11). On the other hand, PMC has been used to treat HCC in Japan mainly (13 15), and there have been reports that PMC is superior to percutaneous ethanol injection for local control of small HCCs (16,17). It appears that in the future, RF ablation and PMC might be alternative therapies to percutaneous ethanol injection. To our knowledge, there have been no studies to compare 331

2 the effectiveness of RF ablation and PMC for local control of HCC. Thus, the purpose of our study was to evaluate the effectiveness of RF ablation and PMC in treating patients with HCC. MATERIALS AND METHODS Patients Characteristics of 72 Patients Treated with RF Ablation or PMC Between March 1999 and October 2000, 72 consecutive patients with 94 HCC nodules were referred to the Department of Radiology at Kyoto University Graduate School of Medicine for ablation therapy. In our hospital, the possible candidates for ablation therapy were patients with a solitary HCC nodule smaller than 4 cm in diameter or those with two or three nodules less than or equal to 3 cm in diameter. Participating patients included 50 men and 22 women aged years (mean age, 63.1 years). The diagnosis of HCC was confirmed in all patients with ultrasonographically (US) guided needle biopsy. US-guided needle biopsy was performed either for a solitary nodule or for the largest nodule in patients with two or three nodules. The human subjects research review boards at our institution approved our study protocol. Before treatment, informed consent was obtained from each patient. The patients were told that RF ablation and PMC were expected to be equally effective for local control of HCC. Patients were assigned, with use of sealed envelopes, to the RF ablation group (n 36) or the PMC group (n 36). The clinical backgrounds of each treatment group are summarized in the Table. Of the 36 patients treated with RF ablation, 25 had a solitary nodule, 10 had two nodules, and one had three nodules; thus, a total of 48 nodules were treated in these patients. Of the 36 patients treated with PMC, 28 had a solitary nodule, six had two nodules, and two had three nodules; thus, a total of 46 nodules were treated in these patients. The pretreatment imaging studies performed were abdominal US and dynamic computed tomography (CT). Abdominal US was performed with a real-time scanner and a 3.5-MHz transducer (model SSD-550; Aloka, Tokyo, Japan). Dynamic CT was performed with a helical CT scanner (model W-3000; Hitachi, Tokyo, Japan). Triple-phase, contiguous, 7-mmthick CT scans were obtained. Nonenhanced CT scans were obtained first. Then, early-phase CT scans were obtained 30 seconds after the initiation of a bolus injection of 100 ml of 65% iopamidol (Iopamiron 300; Nihon Schering, Osaka, Japan). Late-phase CT scans were then obtained 120 seconds after the initiation of the contrast material injection. RF Ablation Characteristic* RF Ablation PMC P Value No. of patients NA Mean age (y) 63.6 (44 83) 62.5 (52 74).54 Male/female patients 26/10 24/12.61 Child-Pugh cirrhosis Class A NA Class B NA Class C 0 0 NA Positive antibody against hepatitis C virus Positive antibody against HbsAg No. of nodules Lesion size Mean size (cm) 2.3 ( ) 2.2 ( ) NA 2 cm NA 2 3 cm NA 3 cm 3 3 NA Serum AFP 200 g/l * AFP -fetoprotein, HBsAg hepatitis B surface antigen. Unless stated otherwise, data are numbers of patients. NA not applicable. Numbers in parentheses are ranges. Data are numbers of nodules. One author (T.S.) performed the RF ablation and PMC procedures. A commercially available generator system (RF 2000; RadioTherapeutics, Mountain View, Calif) was used for RF ablation (10). This system consists of a generator, a monopolar-array needle electrode (LeVeen; RadioTherapeutics), and a dispersive electrode pad that is applied to the patient s skin. The RF generator has a 460-kHz frequency and displays that indicate the tissue impedance value and procedural time. The needle electrode is a 15-gauge insulated cannula with eight or 10 hook-shaped expandable electrode tines with a diameter of 2.0, 3.0, or 3.5 cm at expansion. In the normal liver of a beagle, the mean diameter of tissue ablation achieved by using this electrode with 2.0-, 3.0-, or 3.5-cm expanded tines is approximately cm, cm, or cm, respectively (T.S., Y.Y., unpublished data, 1999). For nodules up to 1.5 cm in diameter, mainly an electrode with 2.0-cm expanded tines was used; for nodules cm in diameter, an electrode with 3.0-cm expanded tines; and for nodules larger than 2.5 cm in diameter, an electrode with 3.5-cm expanded tines. Grounding was achieved by means of attaching a dispersive pad to each of the patient s thighs. Pentazocine (15 mg) (Sosegone; Yamanouchi Pharmaceutical, Tokyo, Japan) was intramuscularly injected 10 minutes before therapy as a premedication for sedation. After the skin surface was disinfected and local anesthesia was induced with 1% lidocaine, a 15-gauge RF probe with 2.0- or 3.0-cm expanded tines, which was connected to the RF generator with a soft cable, was introduced into the center of the nodule with US guidance. The hooks were then deployed in situ in the nodule. With use of an electrode with 2.0-cm expanded tines, treatment was initiated with 30 W of power and increased 10 W/min to 60 W. RF energy was applied until either marked increases in impedance (ie, precipitous decreases in power output as tissue impedance increases markedly owing to coagulation necrosis) were achieved or 15 minutes had elapsed. The second treatment was then applied at the same position until either marked increases in impedance were achieved or 10 minutes had elapsed at 45 W. With use of an electrode with 3.0-cm expanded tines, an initial power of 40 W was applied and increased 10 W/min to 75 W. RF energy was applied until either marked increases in impedance were achieved or 15 minutes had elapsed. The second treatment was then applied at the same position until either marked increases in impedance were achieved or 10 minutes had elapsed at 55 W. An RF probe with 3.5-cm expanded tines was introduced into a cm deep position from the center of the nodule. Treatment was then initiated at 50 W and increased 10 W/min to 90 W. RF energy was applied until either marked increases 332 Radiology May 2002 Shibata et al

3 in impedance were achieved or 15 minutes had elapsed. Then, after the withdrawal of the electrode cm from the first position, the second treatment was initiated at 50 W and increased 10 W/min to 90 W. RF energy was applied until either marked increases in impedance were achieved or 15 minutes had elapsed. Patients who experienced severe pain during or immediately after the treatment received pentazocine (15 mg) intravenously. PMC Therapy The microwave delivery system (Microtaze; Nippon Shoji, Osaka, Japan) consists of a microwave generator, which emits a 2,450-MHz microwave, and a microwave electrode 1.6 mm in diameter and 25 cm in length (13,14). The microwave electrode was connected to the microwave generator by a soft coaxial cable. Pentazocine (15 mg) was intramuscularly injected 10 minutes before therapy as a premedication for sedation. After the skin surface was disinfected and local anesthesia was induced with 1% lidocaine, a 14-gauge guide needle (PMCT NSP; Hakko, Tokyo, Japan) was introduced with US guidance. In the normal liver of a rabbit, the mean diameter of tissue coagulation achieved with a 1.6-mm microwave electrode is about cm (13). For nodules less than or equal to 2.0 cm in diameter, a guide needle was introduced into the center of the nodule, and then the inner needle was removed. Through the outer guiding needle, the electrode was introduced at 5 mm beyond the deep margin of the nodule, and coagulation therapy was performed with a single treatment of 70-W output for 60 seconds. To coagulate an area sufficiently, the electrode was withdrawn every 10 mm to repeat the treatment at 5 mm beyond the superficial margin of the nodule. The electrode and the outer guiding needle were then removed, and the needle track was coagulated with microwaves to prevent bleeding from the liver surface. To coagulate a large area for nodules greater than 2.0 cm in diameter, two to three guide needles were introduced with US guidance in a manner that facilitated optimal thermal coagulation of the entire tumor volume. Then, an electrode was inserted through each outer guiding needle, and multiple treatments were performed in a single session with the procedure just described. Patients who experienced severe pain during or immediately after the treatment received 15 mg of pentazocine lactate intravenously. Effectiveness of RF Ablation and PMC All treatment sessions were completed within 1 month after the beginning of the therapies. Dynamic CT was performed 1 week and 1 month after the initial treatments. The CT scans were interpreted by one author (Y.M.). When a nonenhancing area with a diameter equal to or greater than that of the treated nodule was detected, tumor necrosis was considered to be complete. When nodule enhancement was seen at dynamic CT, tumor necrosis was considered to be incomplete. Additional RF ablation or PMC treatments were performed in nodules that showed incomplete necrosis at dynamic CT performed 1 week after the initial treatment. The therapeutic effect of the therapy was evaluated with dynamic CT 1 month after the initial treatment, and when no enhancing lesion was seen, the therapeutic effect was considered to be complete. When nodule enhancement was still seen, the therapeutic effect was considered to be incomplete. The number of treatment sessions per nodule was compared between the RF ablation and PMC groups. The time required for the ablation therapy, which was defined as the time from skin disinfection to electrode withdrawal, was compared between the RF ablation and PMC groups. Follow-up dynamic CT was performed every 2 months. A newly appearing enhancing lesion in or near the treated nodule or an enlargement of the treated nodule was considered to be residual foci of untreated disease. The follow-up periods ranged from 6 to 27 months (mean, 18 months). Complications Major complications, such as hemorrhage, cholangitis (ie, biloma), liver abscess, hepatic infarction, skin burn, pneumothorax, and tumor dissemination, were assessed by two authors (Y.I., Y.Y.). Complete blood cell counts, platelet counts, coagulation profiles, and liver function tests (eg, for aspartate transaminase, alanine transaminase, alkaline phosphatase, -glutamyl transpeptidase, and total bilirubin levels) were performed 1, 3, and 7 days after the therapy. Statistical Analyses The variables in the RF ablation and PMC groups were compared. For qualitative variables, 2 analysis or the Fisher exact probability test was performed. For continuous variables, the Student t test or Mann-Whitney test was applied. The rates of residual foci of untreated disease from the time of diagnosis of HCC were calculated by using the Kaplan-Meier method. We compared the rate of residual foci of untreated disease in the RF ablation group with this rate in the PMC group by performing the log-rank test. A P value of less than.05 was considered to indicate a statistically significant difference. RESULTS There was no significant difference between the two treatment groups with regard to age or lesion size (Student t test), sex or proportion of patients with elevated serum -fetoprotein levels ( 2 test), Child- Pugh cirrhosis class or number of lesions (Mann-Whitney test), or proportion of patients with positive antibody against hepatitis C virus or proportion of patients with positive hepatitis B surface antigen (Fisher exact probability test) (Table). Therapeutic Effect, Number of Sessions, Time Required for Therapy, and Local Recurrence In the RF ablation group of 36 patients, one to three ablation sessions per nodule were performed, and a total of 55 sessions (mean SD, 1.1 treatments 0.46) were performed in the 48 nodules. A single treatment session was performed in 43 (90%) of 48 nodules, two sessions were performed in three (6%) nodules, and three sessions were performed in two (4%) nodules. The mean time required for RF ablation therapy was 53 minutes 16 per session. Intravenous administration of an analgesic was needed during or immediately after treatment in 10 sessions performed in 10 patients. Of 48 nodules, 46 (96%) showed complete therapeutic effect (Fig 1) and two (4%) had residual lesions, or incomplete therapeutic effect. All 23 nodules less than or equal to 2.0 cm in diameter showed complete therapeutic effect. The two nodules with incomplete therapeutic effect, which had diameters of 2.4 and 3.0 cm, were near the hepatic veins (Fig 2). During followup, residual foci of untreated disease were seen in four nodules (8%). In the PMC group of 36 patients, one to five microwave coagulation sessions Volume 223 Number 2 Radio-frequency Ablation versus Microwave Coagulation of Hepatocellular Carcinoma 333

4 Figure 1. A 2.2-cm-diameter HCC nodule in a 62-year-old man. (a) Transverse early-phase CT scan obtained before RF ablation shows an enhancing tumor (arrows) in the posterosuperior segment of the right lobe of the liver. (b) Right intercostal sonogram shows the expanded hook-shaped tines (arrowheads) of the RF ablation electrode that is introduced into the nodule with US guidance. (c) Transverse early-phase CT scan obtained 1 month after RF ablation shows no enhancement in the tumor area (arrows). (d) Right intercostal sonogram shows that during RF ablation the nodule became hyperechoic owing to vapor produced during treatment. per nodule were performed, and a total of 110 sessions (mean SD, 2.4 sessions 1.0) were performed in the 46 nodules. A single treatment session was performed in 11 (24%) of the 46 nodules, two sessions were performed in 12 (26%) nodules, three sessions were performed in 18 (39%) nodules, four sessions were performed in four (9%) nodules, and five sessions were performed in one (2%) nodule. The mean time required for PMC therapy was 33 minutes 11 per session. Intravenous administration of an analgesic was needed during or immediately after the treatment in 15 sessions performed in 15 patients. Three of these 15 patients could not continue the PMC therapy owing to severe pain, and they underwent the next session while under general anesthesia. Of the 46 nodules, 41 (89%) showed complete therapeutic effect (Fig 3) and five (11%) showed incomplete therapeutic effect. All 19 nodules less than or equal to 2.0 cm in diameter showed complete therapeutic effect. The five nodules with incomplete therapeutic effect were cm in diameter: Three nodules were larger than 3 cm in diameter, and one 2.5-cm-diameter nodule was near the right portal vein. During follow- 334 Radiology May 2002 Shibata et al

5 Figure 2. A 3.0-cm-diameter HCC nodule near the right hepatic vein in a 69-year-old man. (a) Right intercostal sonogram shows the expanded tines (arrowheads) of the electrode that was used to perform RF ablation of a nodule in the posterosuperior segment of the right lobe of the liver. The tines are inside the nodule. (b) Transverse late-phase CT scan obtained after three RF ablation sessions shows residual enhancing lesions (arrows) in the nodule. Therapeutic effect was incomplete. Figure 3. A 2.0-cm-diameter HCC nodule in a 52-year-old woman. (a) Transverse early-phase CT scan obtained before PMC shows an enhancing nodule (arrowheads) in the posteroinferior segment of the right lobe of the liver. (b) Transverse early-phase CT scan obtained 18 months after PMC shows a nonenhancing area (arrows) at the site of the treated nodule. Therapeutic effect was complete, and no local recurrence was noted. up, residual foci of untreated disease were seen in eight nodules (17%), four of which showed incomplete therapeutic effect from PMC. The number of treatment sessions per nodule in the RF ablation group was significantly lower than that in the PMC group (1.1 vs 2.4; P.001, Mann- Whitney test). With this analysis, the nodules were assumed to be statistically independent variables. The mean time required for a PMC session, 33 minutes 11, was significantly shorter than that required for an RF ablation session, 53 minutes 16 (P.001, Mann-Whitney test). There was no significant difference in the rate of complete therapeutic effect between the two groups (96% for RF ablation vs 89% for PMC; P.26, Fisher exact probability test). A graph illustrating the comparison of rates of residual foci of untreated disease between the two groups is shown in Figure 4. The rates of resid- Volume 223 Number 2 Radio-frequency Ablation versus Microwave Coagulation of Hepatocellular Carcinoma 335

6 ual foci of untreated disease in the RF ablation group and in the PMC group were 4% and 10%, respectively, at 1 year after treatment and 12% and 24%, respectively, at 2 years after treatment. There was no significant difference in the rates of residual foci of untreated disease between the two groups (P.20, log-rank test). Complications Major complications occurred with one session (2% per session) performed in one patient (3% per patient) treated with RF ablation and with four sessions (4% per session) performed in four patients (11% per patient) treated with PMC. There was no significant difference in the rate of major complications between the RF ablation and PMC groups (P.67 for difference according to session and P.36 for difference according to patient, Fisher exact probability test). Segmental hepatic infarction occurred in one session, performed in one patient, in the RF ablation group. The patient had prolonged abdominal pain for 2 weeks after therapy and elevated serum aspartate transaminase and alanine transaminase ( 1,000 U/L) levels for 3 days, but he recovered following conservative therapy. In the PMC group, liver abscess occurred with one treatment session performed in one patient, cholangitis with intrahepatic bile duct dilatation occurred with one treatment session performed in one patient, subcutaneous abscess with skin burn occurred in one treatment session performed in one patient, and subcapsular hematoma occurred in one treatment session performed in one patient. A catheter was placed percutaneously for drainage in the patient with liver abscess. The patient with cholangitis recovered following the administration of antibiotics. In the patient with a subcutaneous abscess and skin burn, the abscess was drained by means of skin incision. Conservative management was used for the subcapsular hematoma: It was allowed to absorb without medical intervention such as blood transfusion or transcatheter arterial embolization. No life-threatening complications were observed. In most of the patients without major complications, serum liver enzyme levels increased 1 day after therapy but returned to normal by 7 days after treatment. DISCUSSION Percutaneous ethanol injection has gained fairly wide acceptance as a safe, inexpensive, and effective treatment for small HCCs (2 4). However, percutaneous ethanol injection is occasionally ineffective when there is intra- or extracapsular invasion, because ethanol diffusion is blocked by fibrous tissue (20). The rates of residual foci of untreated disease with percutaneous ethanol injection are not low: 10.5% 26.0% (4,20 22). Tumor regrowth usually occurs from the margin of the tumor because of the nonhomogeneous distribution of ethanol in the tumor. Thermal ablation therapies such as RF ablation and PMC may help those treating these tumors overcome the limitation of pharmacologic therapy diffusion. In a study performed by Livraghi et al (11), the rates of complete necrosis with RF ablation and percutaneous ethanol injection were 90% and 80%, respectively. Horigome et al (17) observed PMC to be superior to percutaneous ethanol injection for the treatment of patients with HCCs less than or equal to 15 mm in diameter. In our study, complete therapeutic effect was achieved in 42 nodules less than or equal to 2.0 cm in diameter: 23 nodules treated with RF ablation and 19 nodules treated with PMC. Thus, RF ablation and PMC may produce sufficient ablation of the tumor and the surrounding liver parenchyma and could become the main treatment for HCCs less than or equal to 2 cm in diameter and the main treatment alternative to percutaneous ethanol injection. Because the coagulated area produced by PMC is smaller than the area produced by RF ablation, more PMC sessions were required to produce complete nodule necrosis (mean number of sessions for PMC vs RF ablation, 2.4 vs 1.1; P.001). Multiple coagulation therapy sessions led to a prolonged treatment course. Three nodules larger than 3 cm in diameter that were treated with PMC showed incomplete therapeutic effect. Although there was no significant difference in the rate of complete therapeutic effect between the RF ablation and PMC groups (96% vs 89%), we believe that RF ablation would be preferable for the treatment of medium-sized nodules that is, those larger than 2 cm in diameter. A common disadvantage of both RF ablation and PMC is the reduced area of coagulation or ablation produced by the cooling effect of hepatic blood flow Figure 4. Graph illustrates comparison of the local recurrence rate between the RF ablation (RFA) and PMC (pmct) groups (P.20, logrank test). (23,24). Two nodules treated with RF ablation and one nodule treated with PMC near a hepatic vein or portal vein showed incomplete therapeutic effect, presumably because of the cooling effect. Thus, ablation therapy performed during interrupted hepatic blood flow with balloon occlusion of the hepatic artery and hepatic vein is another treatment option (23,24). This technique is more invasive, however, because the ablation must be performed during angiography. In such cases, RF ablation followed by percutaneous ethanol injection should be effective, because the size of the area ablated with ethanol is not affected by the cooling effect. Three types of RF electrodes are currently available commercially: two brands of retractable needle electrodes (model 70 and model 90 Starburst XL needles, RITA Medical Systems, Mountain View, Calif; LeVeen needle electrode, RadioTherapeutics) and an internally cooled electrode (Cool-Tip RF electrode; Radionics, Burlington, Mass) (25,26). de Baere et al (27) found that the internally cooled electrode produced substantially larger lesions than did the expandable needle in animal livers. However, to our knowledge, there are no reports of comparisons of the effectiveness of these RF electrodes in human studies. The rate of complete necrosis of HCC treated with internally cooled electrodes has been reported to be 90% (47 of 52 nodules) (11), and the rates 336 Radiology May 2002 Shibata et al

7 of residual foci of untreated disease treated by using Starburst XL needle electrodes has been reported to be 4% (one of 24 nodules) (9). Our results with the Leveen needle electrode (rate of complete therapeutic effect, 96% [46 of 48 nodules]; rates of residual foci of untreated disease, 4% at 1 year and 12% at 2 years) were equivalent. Also, our rates of residual foci of untreated disease were equal to or better than the rates of foci treated with percutaneous ethanol injection (10.5% 26.0%) (4,20 22). There was no significant difference in the rate of major complications between the RF ablation and PMC groups. In the PMC group, four patients had one of the following complications: liver abscess, cholangitis, bile duct dilatation, or subcutaneous abscess with skin burn. Multiple microwave treatments might increase the risk of damage to the biliary tract and/or cause infection. The microwave electrode consists of inner and outer conductors. For heat and electric insulation, the space between these two conductors is filled with silicon gum and polytetrafluorethylene (13), but the insulation for heat may not be complete. The incomplete insulation of a microwave electrode may induce skin burn. Both RF ablation and PMC are currently undergoing major modifications, so the new techniques may produce larger areas of tumor coagulation or ablation in the future. In conclusion, the current RF ablation and PMC techniques thus far have had equivalent therapeutic effectiveness, complication rates, and rates of residual foci of untreated disease; however, RF ablation offers the advantage of tumor ablation achieved in fewer sessions. We prefer RF ablation over PMC for the treatment of small HCCs. References 1. Munoz N, Bosch X. Epidemiology of hepatocellular carcinoma. In: Okuda K, Ishak KG, eds. Neoplasms of the liver. Tokyo, Japan: Springer-Verlag, 1987; Shiina S, Tagawa K, Niwa Y, et al. 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