I. Overview
Local ablation is one of the important tools for the treatment of liver tumors, including physical ablation and chemical ablation. Radiofrequency ablation (RFA) is one of the commonly used physical ablation treatment methods. Its principle is to apply electromagnetic heat energy generated by electromagnetic waves with frequency <30MHz (usually between 375-500kHz) to cause tissue coagulation and necrosis. The purpose of inactivating the tumor is achieved. There are three treatment routes: percutaneous, trans-laparoscopic and open surgery.
Percutaneous RFA is an ablative treatment for tumor under image guidance, which includes x-ray fluoroscopy, ultrasound, CT and MRI, etc. It has the advantages of minimally invasive, relatively safe, exact efficacy and repeatable, and is the preferred treatment for early-stage primary liver cancer that is not suitable for surgical resection or liver transplantation; for middle and late stage primary liver cancer and metastatic liver cancer that are not suitable for surgical resection, RFA is also a comprehensive treatment. RFA is also one of the comprehensive treatment methods for middle and advanced primary liver cancer and metastatic liver cancer not suitable for surgical resection. In addition, RFA can also be applied to the ablative treatment of benign solid tumors of the liver.
Although RFA for percutaneous liver tumors is a minimally invasive treatment technique, there are potential treatment risks and even serious complications that may endanger patients’ lives. In order to better standardize the operation technique to reduce complications and improve the therapeutic effect, the Interventional Radiology Group of the Chinese Medical Association has formulated this expert consensus to guide clinical practice.
Second, image guidance
X-ray fluoroscopy, ultrasound, CT and MRI can be used for the guidance and monitoring of percutaneous liver tumor RFA treatment, but ultrasound and CT are mostly used for guidance and monitoring.
1. X-ray fluoroscopic guidance: X-ray fluoroscopic guidance for puncture localization needs to be combined with preoperative arterial chemoembolization or arterial embolization (transeatheterarterialchemoembolization0rtranscatheterarterialembolization. TACE or TAE) to mark the tumor by iodized oil. The tumor is then treated with RFA. The disadvantage is that it is difficult to assess the ablation effect intraoperatively. The operator and the patient are exposed to a certain dose of x-ray radiation.
2. Ultrasound guidance: The advantages of ultrasound guidance are real-time guidance of puncture and simple operation; the approximate extent of tumor destruction can be assessed according to the transient hyperechoic area produced during ablation; ultrasonography can also immediately evaluate the inactivation of tumor. The disadvantage of ultrasound guidance is that there are blind areas in image guidance: the image quality is easily disturbed by bubble artifacts generated during the ablation process, which affects the ablation treatment at the next site. The application of ultrasound and CT or ultrasound and MRi image fusion technology can compensate the shortage of ultrasound guidance alone to a certain extent.
3. CT guidance: CT image with high density resolution can clearly show the needle path, the relationship between RF electrode needle and tumor and surrounding tissues, with precise positioning and no blind area; the approximate extent of tumor destruction can be evaluated according to the hypodense area produced by tissue necrosis after ablation, and well can be applied to evaluate tumor inactivation by enhancement scan. The disadvantage is that the puncture is somewhat blind, and the process of needle entry cannot be guided in real time, and repeated puncture and scanning are often required; in addition, the patient is exposed to a certain dose of x-ray radiation.
4. MRI guidance: The advantages of MRI guidance are high soft tissue contrast and spatial resolution, clear display of tumor location and relationship with surrounding tissues, accurate positioning; imaging in any plane, which is helpful to select the best needle path; no X-ray radiation; real-time monitoring of temperature field changes in the ablation area, and evaluation of the approximate extent of tumor destruction. The disadvantage of MRI guidance is that it requires magnetically compatible instruments and is relatively expensive.
In practice, the appropriate guidance method can be selected according to the specific situation, and multiple guidance methods can also be combined.
Radiofrequency electrode needle
At present, RF electrode needles can be divided into 2 types of unipolar and bipolar. Single or multiple electrode needles can be used to directly puncture into the tumor for single point or multi-point superimposed conformal RFA treatment.
1. Monopolar RF electrode needle: there is 1 active electrode with 1 or several circuit electrode plates at the same time. It includes different designs such as multi-tip extension type, cold circulation type and perfusion type.
(1) Multi-tip extension type RF electrode needle: has a thicker cannula needle. Multiple sub-electrode needles can be extended within it.
(2) Cold circulation type RF electrode needle: there is a closed tube lumen inside the electrode needle, and the active end of the electrode needle can be cooled by injecting cooling saline etc. into the lumen to prevent charring of the tissue around the active end of the RF electrode needle. Cold circulation type RF electrode needle can be divided into single bundle type and three needle cluster type, the latter is larger than the former single point ablation volume.
(3) Perfusion type RF electrode needle: there are small holes at the tip of RF electrode needle, through which liquid (often saline) can be injected into the ablated tissue to prevent tissue charring and increase the ablation volume.
2. Bipolar radiofrequency electrode needle: It consists of 2 electrode needles (active electrode and circuit electrode respectively) or the tip of 1 electrode needle has both active electrode and circuit electrode, without circuit electrode plate. Patients with metal implants and pacemakers in the body should choose bipolar radiofrequency electrode needles.
IV. Indications and contraindications
1. Indications.
(1) Primary hepatocellular carcinoma: single tumor ≤5cm in diameter that is not suitable for surgical resection. (1) Primary hepatocellular carcinoma: single tumor ≤5cm in diameter not suitable for surgical resection, or multiple (3) tumors with maximum diameter ≤3cm, without vascular, bile duct and adjacent organ invasion and distant metastasis; single tumor >5cm in diameter not suitable for surgical resection, or multiple tumors with maximum diameter >3cm, RFA can be used as part of the radical or palliative comprehensive treatment, combined with TACE or TAE before RFA treatment is recommended; RFA can also be used for tumor control before liver transplantation RFA can also be used to control tumor growth before liver transplantation and for the treatment of intrahepatic recurrence and metastasis after transplantation.
(2) Metastatic liver cancer: If the primary lesion outside the liver can be effectively treated, RFA treatment for metastatic liver cancer can be performed. There is no consensus on the regulation of tumor size and number in ablation therapy. In most clinical trials, the maximum tumor diameter ≤ 5 cm and the number ≤ 5 are considered as indications for treatment.
(3) Hepatic hemangioma: if there are clinical symptoms and the tumor diameter is >5cm with obvious tendency to increase, RFA can be one of the treatment methods.
Contraindications: (1) diffuse lesions; (2) combined extrahepatic vascular and bile duct cancer emboli; (3) tumor invasion of cavernous organs; (4) liver function Child-Push grade C; (5) uncorrectable coagulation dysfunction; (6) patients in acute infection, especially biliary infection; (7) heart, lung, liver, kidney and other important organ failure; ( 8)Eastern Oncology Collaborativeoncologygroup (ECOG) physical status score H vice >2 (Table I); (9)patients during pregnancy.
Table 1ECOG physical status score criteria
V. Preoperative preparation
I. Equipment and materials: radiofrequency ablation therapy instrument, radiofrequency electrode needle, puncture frame or positioning navigation system, guidance needle (for CT or MRI guidance), etc. To ensure the image guidance equipment and RF ablation therapy instrument are in normal working condition. for MRl guidance, magnetic compatible equipment and consumables are required. General anesthesia should be equipped with ventilator and related equipment.
2. Routine examination: Patients need to receive routine blood, urine and stool, liver and kidney function, coagulation function, tumor markers, blood type examination and infection screening, electrocardiogram, X-ray chest X-ray, etc. within 2 weeks.
3. Imaging examination: Patients need to undergo liver ultrasound (ultrasonography if available), enhanced CT or enhanced MR examination within 2 weeks, and PET-CT examination is also feasible to observe tumor location, size, number, shape, relationship with large blood vessels, bile ducts and surrounding organs, and to guide the needle approach path. It is recommended that at least one of enhanced cT or enhanced MRI examination should be performed before surgery.
4. Pathological examination: In order to clarify the diagnosis, a puncture biopsy pathological examination of the lesion is recommended.
5. Develop ablation plan: Determine the appropriate guidance method, RF electrode needle type and model according to the patient’s condition and hospital conditions. Determine the puncture point, needle approach path and needle deployment plan.
6. Drug preparation: Prepare anesthesia, sedation, analgesia, antiemetic and antihemorrhagic drugs, emergency equipment and drugs before surgery.
7. Patient preparation: (1) the patient and family (delegate) sign the informed consent form for surgery; (2) no diet 4h before local anesthesia, no food 12h before general anesthesia, no water 4h before; (3) routine skin preparation in the operating area; (4) establish intravenous access.
VI. Operation steps
1. Anesthesia: The most commonly used method is local anesthesia at the puncture point combined with intraoperative intravenous sedation and analgesia. The advantages of this anesthesia method are simple operation, small risk, and good intraoperative patient cooperation. For children, patients who cannot cooperate intraoperatively, expected long operation time, and tumors located in pain-sensitive areas, general anesthesia is used. Pre-anesthesia assessment can refer to the grading criteria of American Society of Anesthesiologists (ASA) (Table 2), and only patients with ≤ grade III can be treated with RFA, and patients’ vital signs and oxygen saturation can be monitored intraoperatively.
2. Preoperative localization: preoperative image localization was performed to select the best treatment position and needle path. The needle path must pass through part of the liver tissue, avoiding large vessels, bile ducts and important organs, and marking the puncture point.
3. RFA treatment: The surgical area is routinely disinfected, toweled, and the puncture site is locally anesthetized. Under image guidance, the RF electrode needle is punctured along the needle path to the ablation target area. cT and MRI guidance, the RF electrode needle can be punctured under the guidance of the needle or directly, and the needle should be advanced in steps. Adjust the puncture angle and depth according to the pre-ablation target, and fix the RF electrode needle after scanning to confirm that the active end of the RF electrode needle reaches the pre-ablation target. And record the angle and depth of the RF electrode needle to avoid the displacement of the RF electrode needle during the procedure.
During RFA, the treatment parameters are set according to the type of RF ablation therapy instrument, the type of RF electrode needle, the size of tumor and its relationship with the surrounding tissue structure. Ultrasound guidance should ablate the tumor in deeper parts first and then in shallower parts. To ensure the effect of tumor ablation treatment, the ablation range should include the tumor and the peritumor 0.5-1.0 cm liver tissue to obtain the ablation margin. Specifically.
(1) Small tumor: for tumor number ≤ 3 and diameter < 3cm, single completion of RFA treatment.
(2) Medium tumors: tumors with diameters of 3-5 cm, single multi-point superimposed to complete RFA treatment.
(3) Large tumors: for tumors >5cm in diameter, it is recommended to apply TACE or TAE treatment one before RFA. For RFA treatment of large tumors, multi-point superimposed conformal ablation therapy is used. According to the tumor condition and combined with the patient’s liver function and physical condition, the treatment plan can be developed, and the ablation treatment can be completed in a single time or in several times.
(4) Tumors adjacent to gallbladder, gastrointestinal tract and diaphragm: In the selection of guidance mode, try to choose the guidance mode with clear tumor display. Firstly ablate the tumors adjacent to important organs, and also combine chemical ablation for this part of tumors, and take certain protective measures to avoid thermal damage to adjacent organs if necessary.
(5) Tumors protruding from the surface of the liver: For tumors in this area, direct puncture should be avoided, and the needle path needs to pass through the liver tissue to reach the tumor. Preoperative TACE or TAE treatment is recommended, and direct puncture of the tumor can be performed after dense iodinated oil deposition in the tumor.
(6) Hepatic caudate lobe tumor: avoid important organs such as inferior vena cava, portal vein, major bile ducts and gastrointestinal tract, and puncture to the tumor through the right or left hepatic approach.
4. Post-treatment treatment: The approximate extent of tumor destruction is assessed according to the transient hyperechoic area shown by ultrasound, hypointense area shown by CT and temperature field shown by MR during tumor ablation; ultrasonography, enhanced cT and enhanced MRI examination are also feasible for assessment. After confirming that the ablation area reaches the pre-ablation range, withdraw the RF electrode needle and perform needle ablation at the same time, and confirm whether there are complications such as bleeding and pneumothorax in parallel with the imaging examination.
5. Precautions during the treatment.
(1) Perform breathing and breath-holding training for patients before puncture to ensure that the needle path is relatively consistent with the relationship between the tumor location.
(2) The puncture path should pass through part of the liver tissue and avoid direct puncture of the tumor as much as possible.
(3) The puncture should be accurately positioned to avoid multiple punctures leading to tumor implantation, adjacent tissue damage or tumor rupture and bleeding.
(4) If the RF electrode needle has been punctured into the tumor but needs to be adjusted, it should be adjusted after in situ ablation to avoid tumor implantation.
(5) For multiple tumors RFA, if the RF electrode needle needs to leave the liver envelope and re-puncture the position. Needle ablation must be performed.
VII. Postoperative treatment
After surgery, cover the puncture site with sterile gauze, 24h cardiac monitoring, if necessary, extend the monitoring time. After ablation treatment of tumors adjacent to the gastrointestinal tract, the fasting time should be extended according to the situation. Routine blood, liver and kidney function, and routine urine examination should be performed within 3 d after surgery. Rehydration, liver protection and symptomatic treatment according to the situation.