Radiofrequency ablation (RFA) has the advantages of safety, minimally invasive, less damage to liver function and fewer complications, and has become an important tool in the comprehensive treatment of liver cancer, and has achieved relatively satisfactory results. The progress of its treatment is now reviewed in the context of our center. The basic equipment of RFA includes radiofrequency generator, treatment electrode and neutral electrode, which together with the patient form a closed loop, among which the treatment electrode is the key technology. In the mid-1980s, single-electrode radiofrequency was used to treat liver tumors; in the mid-1990s, multi-electrode radiofrequency, i.e., cluster electrode, was used in clinical practice; in recent years, the third-generation electrodes, such as cluster hollow-cooling electrode and saline-enhanced hollow-cooling composite electrode, have been widely used, so that the treatment methods and efficacy of RFA for liver cancer have made a qualitative leap, and the maximum tissue ablation range has reached 250 px [1]. The basic principle of RFA treatment: the electrode warhead emits medium-high frequency radiofrequency waves to excite tissue cells to undergo plasma shock, and the temperature generated by the ions hitting each other can reach 80-100 ℃, causing coagulative necrosis of tumor cells. The inactivated tumor tissues after the effect of high temperature, the cellular immune phenotype changes, which facilitates the attack of the body’s immune system. The blood supply to the tumor is affected by the coagulation of the vascular tissue around the tumor. The tumor body loses heat slowly after heating, and the temperature inside the tumor body rises faster than normal tissues, which makes it more susceptible to necrosis than normal tissues. The accumulation of acidic intracellular metabolites after heating has a killing effect on tumor cells [2]. 2. Indications and contraindications Indications: The selection of indications is not yet consistent. Referring to the NCCN guidelines for the treatment of hepatocellular carcinoma, the Liver Surgery Group of the Chinese Society for Surgery recommends the following indications for RFA treatment of hepatocellular carcinoma: ① good general condition, no significant organic lesions of heart, lung, kidney and other important organs, good functional status or only mild impairment; normal liver function or only mild impairment, grade 1 or grade 2 according to liver function classification. ② Single cancer foci or less than 5 cancer foci; tumor diameter less than 5 cm. ③ Recently recurred hepatocellular carcinoma after hepatectomy, unsuitable or patients unwilling to undergo another hepatectomy. Our center is one of the earlier units in China to carry out radiofrequency treatment for hepatocellular carcinoma, and has completed 275 cases with 338 cases since 2001. The indications used are: ① Small hepatocellular carcinoma that is not suitable for surgery. ② Those located in Ⅳ, Ⅴ, Ⅷ (central type) or those with large cancer that cannot or is difficult to be resected. ③ Multiple tumors in the liver. ④ Recurrent small hepatocellular carcinoma which is difficult to be resected by surgery again. ⑤ Elderly and frail patients who cannot tolerate hepatectomy. (6) Those who are not contraindicated to surgery but do not want to operate. ⑦ For hepatocellular carcinoma larger than 5 cm, radiofrequency treatment can be performed after multiple or multi-point radiofrequency treatment or hepatic artery chemoembolization. ⑧ For patients with tumor close to the first hepatic portal; mild jaundice; small amount of ascites; liver function Child C, which can be changed to Child B after treatment; liver cancer with obstructive jaundice, the jaundice obviously subsides after drainage; patients who have been treated with TACE, after accumulating certain experience, can cautiously try RFA treatment. The inactivation effect of radiofrequency treatment for small hepatocellular carcinoma has been fully affirmed. For single nodule with diameter > 10 cm, the phenomenon of three-dimensional space leakage is easy to occur due to the difficulty of spatial localization, and the blood circulation status of liver tissue, the tissue characteristics of tumor and the richness of blood transport make the heat dissipation effect individualized. Therefore, radiofrequency treatment of large hepatocellular carcinoma is still a difficult problem to be solved. The authors have also treated single nodules >10 cm in diameter with RFA in 3-4 fractions and achieved a long survival with tumor. Contraindications: RFA is generally contraindicated in patients with grade C liver function, severe bleeding tendency, massive ascites, severe jaundice, and combined portal vein thrombosis. 4. Treatment route RFA can be performed under ultrasound, CT, or MRI guidance with skin puncture; it can also be performed under laparoscopic ultrasound guidance or under direct laparoscopic or open visualization. In Japan, Minami et al. first proposed RFA for subdiaphragmatic liver lesions near the top of the diaphragm in 2003 [3]. This method is easy to operate, ensures the display of the lesion by ultrasound, provides a sound window for ultrasound with the injection of artificial pleural fluid, makes the tumor on the diaphragmatic surface of the liver clearly displayed, facilitates the treatment of RF ablation, improves the safety of treatment, and is a safe method for the treatment of liver tumors. It is especially suitable for tumor diameter < 5 cm, liver function grade A or B, and tumor located in the diaphragmatic surface of the liver (segment VII or VIII). The efficacy of radiofrequency ablation therapy is usually evaluated by serum oncological parameters and imaging. Tateishi R et al. reported 416 cases of HCC treated with radiofrequency, and AFP, des-gamma-carboxy prothrombin (DCP) and lentil agglutinin-affinity AFP heteroplasm (lens culinaris agglutinin-) were measured before and two months after surgery. In 227 cases of postoperative recurrence, univariate analysis revealed that the recurrence-related factors were: preoperative platelet count, tumor size and number, AFP, DCP, and AFP-L3. Multivariate analysis showed that the recurrence-related factors were: preoperative and postoperative AFP > 100ng, AFP-L3, and AFP-L3. 100ng, AFP-L3>15%. In contrast, those with positive preoperative AFP and AFPL3 that turned negative postoperatively did not correlate well with recurrence [4]. It is generally believed that ultrasound has limited evaluation of RFA treatment, Hotta N et al. reported that 4-dimensional instant ultrasound can clearly show the relationship between the RFA electrode needle and the target target destruction area, which can accurately evaluate the efficacy of RFA for hepatocellular carcinoma [5].Kisaka Y et al. concluded that the application of ultrasonography can significantly improve the accuracy of the evaluation of the efficacy of RFA for hepatocellular carcinoma [6]. CT is the gold standard for the assessment of RFA efficacy. 1 month after treatment, a review of CT with no enhancement of the lesion after hypointense enhancement scan of the destroyed area can be considered as complete destruction; if there is a partially enhanced area, it indicates that there is still residual tumor. The long-term follow-up data of a group of multislice spiral CT by Filippone A showed that the failure of RFA treatment was manifested by the enlargement of the destruction area and/or intensification of the lesion [7].Ninomiya T. et al. used dynamic computed tomography to examine the destruction lesion of hepatocellular carcinoma before and one week after RFA, and the efficacy of RFA treatment could be accurately assessed by multidimensional plane reconstruction [8]. 6. treatment effect The therapeutic effect of RFA for small hepatocellular carcinoma is largely confirmed. kim YS et al. reported 62 cases with diameter ≤100px treated by percutaneous RFA, with a mean follow-up of 19.1 months, one-year survival rate of 82% and two-year survival rate of 63% [9]. wakai T. et al. reported 21 cases with diameter ≤100px treated, with a mean follow-up of 69 months and mean survival of 66 months [10]. Hong Kong Chen MH. et al. reported 205 cases of HCC with a total of 308 lesions treated with RFA, with a mean lesion diameter of 102.49999999999999 px, a complete destruction rate of 95.8% (295/308), a local recurrence rate of 10.7% (33/308), and survival rates of 89.6%, 69.4%, and 3 years, respectively, in one, two, and 59.6%, including 60 cases of stage I/II HCC with survival rates of 93.7%, 87.1%, and 76.2% at one, two, and three years, respectively [11]. We treated 275 cases with 338 RFA from 2001 to 2006, with a one-year cumulative survival rate of 79% and a three-year survival rate of 41.7%. Among them, the one-, two- and three-year cumulative survival rates of 87 cases of small hepatocellular carcinoma less than 125 px in diameter were 91.0%, 76.7% and 69.7%, respectively, while the one-, two- and three-year cumulative survival rates of 40 cases of small hepatocellular carcinoma in the surgical group during the same period were 90.0%, 82.9% and 75.4%, respectively, and the difference between the two survival curves was not statistically significant by Log-Rank test (χ2 = 0.99, P = 0.32). The tumor-free survival rates of the radiofrequency group and the surgical group at one, two and three years were 57.3%, 40.3%, 35.3% and 71.1%, 45.7%, and 30.9%, respectively, with no statistically significant difference between the two groups by Log-Rank test (χ2 = 0.06, P = 0.80). Thus, it was concluded that for small hepatocellular carcinoma, radiofrequency ablation has similar efficacy to surgical resection. Radiofrequency treatment is less invasive and reproducible, and has important clinical application in the treatment of small hepatocellular carcinoma. 7. Complications Radiofrequency is a safe and minimally invasive treatment method with few complications in general. Chen MH et al. reported that in 295 cases with 574 treatments for 308 lesions, the complication rate was 1.4% (8/574 ), including 3 bleeds, 4 adjacent organ injuries and 1 needle tract metastasis. Our 275 cases with 338 treatments had a complication rate of 1.5% (5/338 ), including 2 hemorrhages, 1 hepatobiliary stenosis, 1 needle metastasis and 1 cardiac arrest. Postoperative bleeding was mainly from the needle tract, and we mostly increased the temperature to 90-100 ℃ after RF to char the needle tract to prevent bleeding.Carrafiello G reported 126 RFAs in 96 cases with 150 lesions from 2002-2005, and 2 cases with severe bleeding complications were successfully stopped by TAE.12]. Pneumothorax is prone to occur when the tumor is treated with percutaneous hepatic puncture radiofrequency close to the diaphragm and can be prevented by using artificial pleural fluid or direct laparoscopic/surgical view. For high-frequency thermogenesis induced vagal hyperreflexia causing cardiac arrhythmia and cardiac arrest, we should pay great attention to it, and we had one case, which was rescued in time and turned to safety. If the radiofrequency treatment is not done properly, it can cause tumor implantation and metastasis through the needle tract [13]. The complications reported in the literature include fever, infection, skin electrode burns, liver function impairment, and perforation due to gastrointestinal injury. With the application of more advanced positioning and monitoring devices such as fluoroscopic CT, MR or acoustic microbubble contrast-enhanced ultrasound systems, improvements in treatment electrodes such as saline-enhanced umbrella electrodes, bipolar saline-enhanced electrodes, improved needle deployment methods and puncture techniques, overcome the disadvantages of incomplete ablation due to incomplete necrosis of larger tumors and lower actual temperature at the tumor foci than the designed treatment temperature. RFA alone or in combination with surgical resection, liver transplantation, TACE, PEI, chemotherapy, etc. is expected to achieve better efficacy in the treatment of liver cancer.