After more than 20 years of development, a large number of clinical studies have confirmed the advantages of percutaneous ablation therapy for hepatocellular carcinoma, such as precise efficacy, minimally invasive, simple operation, low cost, repeatability, and high quality of life after the procedure. Several recent prospective randomized controlled clinical studies have demonstrated that percutaneous ablation for early-stage HCC can achieve long-term survival comparable to that of surgical procedures. The newly published guidelines of the American College of Hepatology also clearly indicate that percutaneous ablation, together with partial liver resection and liver transplantation, can be used as a radical treatment for early-stage HCC.
Precision ablation therapy for hepatocellular carcinoma is a brand new concept, which is characterized by the use of various known advanced technical means to precisely control all aspects of ablation therapy, ultimately achieving complete destruction of the tumor with minimal damage to adjacent tissues.
1.Pre-operative planning
Compared with surgical resection, ablative treatment for liver cancer includes several different aspects, although it is relatively simple. Pre-operative planning is the most important part, which needs to take into account patient factors, tumor factors and imaging factors.
Patient factors: mainly include the underlying disease and liver function status, other factors include age, physical condition, compliance, etc.
Tumor factors include the degree of tumor progression, tumor location, relationship with surrounding key structures, and the presence of tumor envelope. Some scholars can use the relevant software to simulate the puncture path and needle deployment before the operation, so as to make an accurate preview of the ablation operation.
The image display factors mainly include the visibility and clarity of the lesion on the image.
Based on the above factors, the operator needs to decide the proposed anesthesia, patient position, image guidance method, the auxiliary means to be used, the choice of ablation means, and the needle deployment plan of ablation needle, etc. before the operation.
2.Intraoperative
Image-guided general gray-scale ultrasound is listed as the preferred image guidance method for percutaneous ablation treatment of liver cancer because of its easy operation, real-time, convenient movement, relatively low price and no radioactivity. Successful ablation can be achieved in most cases by using ordinary ultrasound instruments. However, there are some limitations of general ultrasound, which may not be applicable to some cases.
(1) There are “dead spots” in ultrasound examination, and some lesions located at the top of the diaphragm and the outer edge of the left liver cannot be displayed due to the influence of lung gas or intestinal gas; some lesions located at the lower edge of the rib cage cannot be displayed.
(2) Echo characteristics of the lesion: Some of the lesions appear as isoechoic on the ultrasound image and are not clearly demarcated from the surrounding tissues.
(3) Focal boundaries: Some HCC lesions showed infiltrative growth into the surrounding liver and the actual contour and size of the lesions were not known.
(4) Liver background: Most HCC is combined with cirrhosis and the lesions may be poorly demarcated from the surrounding tissues.
(5) When multiple lesions are present or when HCC coexists with cirrhotic nodules, it is not easy to identify the lesion to be treated.
(6) Some of the lesions are shown on CT or MRI but not on ultrasound.
(7) When the residual or locally progressive lesions are supplemented with ablation again after ablation therapy or TACE therapy, the residual cancer foci cannot be distinguished from necrotic tissue by ordinary ultrasound.
(8) In the case of multi-point ablation, it is difficult to accurately guide the next needle placement when the needle is placed again after the first ablation because the previous ablation produces a hyperechoic mass in the lesion area.
In view of the above possible problems, some thoughts are needed on the imaging guidance methods
(1) Ultrasonography guidance: Real-time ultrasonography can show the rich blood supply inside the surviving tumor tissue, and therefore can distinguish the tumor from the surrounding liver tissue and necrotic tissue. Ultrasonography is increasingly useful in preoperative planning and intraoperative guidance, and can be used to show the actual size and progression of the tumor, especially in cases where the lesion is not clearly visible or in cases where supplemental ablation requires differentiation between the cancerous and necrotic tissues.
(2) Fusion image guidance: Fusion image method, also known as virtual navigation technique. The CT, MRI or 3D ultrasound images are imported into the ultrasound instrument by DICOM, and the CT, MRI or 3D ultrasound tomographic images are matched with the real-time ultrasound images and the same cross-section is obtained with the help of magnetic field spatial position locator. With the help of fusion images, especially the enhanced CT or MRI images, it can not only display lesions that are difficult to be displayed by ordinary ultrasound, but also use the fusion images to make careful needle planning for larger tumors and improve the local treatment effect.
(3) Three-dimensional ultrasound guidance: Three-dimensional ultrasound can observe the area to be ablated from different angles, and at the same time can observe from the coronal plane which is not easily obtained by two-dimensional ultrasound, improving the confidence level of the operator. Three-dimensional ultrasound is particularly suitable for observing extendable electrode needles or for determining the position of the needle tip and the relationship between the electrode needle and the surrounding critical structures.
(4) Dual probe ultrasound guidance: Dual probe ultrasound guidance can display the images obtained from two different probes sweeping from different angles on the same screen, so that when one probe is used for guidance and monitoring, the other probe can be used to observe the ablation foci and the position of the ablation foci in relation to the surrounding structures from a different angle.
(5) Robotic system: The robotic system for image guidance is currently under development. The system mainly consists of three modules: ultrasound image navigation, puncture robot and spatial positioning device. Preoperatively, a 3D reconstruction of the liver tumor area is performed to simulate the puncture needle path and plan needle placement. Using the blood vessels in the liver to match the model with the patient entity, the position in the preoperative model can be transformed into the joint angle of the robot. Finally, the robot system is dragged to accurately deliver the puncture needle to the designated lesion location for microwave ablation.
Ablation options
There are various ablation methods, including chemical ablation and thermal ablation. The former mainly includes anhydrous alcohol ablation, acetic acid ablation, high-temperature saline ablation, high-temperature distilled water ablation, and high-temperature carboplatin ablation, etc., while anhydrous alcohol ablation is the representative. The latter mainly has radiofrequency ablation, microwave ablation, laser ablation, cryoablation, high-intensity focused ultrasound ablation, etc., while radiofrequency ablation or microwave ablation is the main representative.
Even if the same is RF ablation, it also includes a variety of complex needles to choose from, commonly used are single needle electrode, cluster needle electrode, multi-head extendable electrode (including front extension type and side extension type), hollow cooling electrode, dual source electrode and so on. When selecting electrode needles, the ablation range and ablation pattern of various types of electrode needles, as well as the location of the lesion, patient compliance and other factors should be fully considered.
In addition to the commonly used PTC needle or special anhydrous alcohol needle, in recent years, there is a kind of puncture needle with multiple expandable sub-needles, which can extend three sub-needles after the puncture needle is unfolded, covering a diameter of 5 cm. there are four lateral holes at the tip of each sub-needle, so there are 12 lateral holes in total. After the injection of anhydrous alcohol, the alcohol can flow out from the 12 side holes, which makes the alcohol more evenly distributed in the tumor, and a single large dose can effectively treat tumors with an intact envelope of 3~5 cm in diameter.
Multiple ablation methods can be used in combination. The combination of radiofrequency ablation and anhydrous alcohol ablation can significantly increase the ablation range and is suitable for tumors with a diameter of 3 cm or more. In combination, anhydrous alcohol ablation is usually used first and then RF ablation is started. For some tumors that are close to dangerous areas (such as intestine, stomach, bile duct, gallbladder, liver gate, heart) or close to large blood vessels that may have heat sink effect resulting in incomplete ablation, anhydrous alcohol can be used on the side close to dangerous areas or large blood vessels, while radiofrequency ablation is used on the other side.
Adjuvant means
The application of various adjuvant means is also indispensable to expand the indications for ablation treatment of hepatocellular carcinoma and reduce postoperative complications.
(1) Artificial pleural fluid: artificial pleural fluid is injected into the thoracic cavity with saline or 5% glucose liquid by using artificial pneumoperitoneum needle to separate the bottom of the lung from the diaphragm and move the lung upward. With the sound window formed by the saline or glucose solution in the thoracic cavity, the lesion that was previously obscured by the lung gas due to its high position can be fully displayed on normal ultrasound, which improves the accuracy of RF ablation treatment. When the puncture route unavoidably passes through the chest cavity and may damage the lung tissue, the use of artificial pleural fluid to elevate the lung tissue can provide a new puncture route.
(2) Artificial ascites: artificial ascites is saline or 5% glucose solution injected into the abdominal cavity, and the injected dose can range from tens of milliliters to hundreds of milliliters. It is mainly used in the following situations: when the lesion is on the outer edge of the liver near the intestinal canal, the injection of artificial ascites can separate the intestinal canal from the liver to avoid damaging the intestinal canal during thermal ablation; when the lesion is located high near the top of the diaphragm, the injection of artificial ascites can clearly display the lesion that could not be clearly displayed; when the lesion is located near the liver surface, the artificial ascites can separate the liver peritoneum from the abdominal wall to avoid damaging the abdominal wall during thermal ablation.
(3) Preoperative TACE: Preoperative TACE can reduce the tumor load and necrosis of large part or part of the tumor in patients with medium to large liver cancer or multiple liver cancers. Generally, ablation therapy is performed within 5-7 days after TACE when liver function is basically normalized, which can achieve better local efficacy and multiply the effect with half the effort.
(4) Combined radioactive particle implantation: Radioactive particle implantation is more common with 125I. Particle implantation on one side of the lesion near the risk area or on the peripheral part of medium and large hepatocellular carcinoma after ablation can enhance the local curative effect of ablation therapy.
3.Postoperative efficacy assessment and follow-up
The necrotic tissue is not removed from the in situ after ablation, but the blood supply has been lost. Enhanced imaging technology can dynamically reflect the changes of blood supply in the ablation area, and is the main tool for judging the local efficacy and follow-up after ablation. The enhancement imaging technique used in the past is mainly enhanced CT or MRI, which is also the gold standard method to determine the local efficacy at this stage.
Ultrasonography: The imaging effect of ultrasonography is similar to that of enhanced CT or MRI, but it has the advantages of easy operation, rapidity, no allergy, no radioactivity, and relatively low price. A recent multicenter study also confirmed that ultrasonography has the same value as enhanced CT or MRI in evaluating the local efficacy of liver cancer after ablation. Therefore, this technique is recommended to be performed in hospitals that have the conditions.
Three-dimensional ultrasonography: ultrasonography also has some limitations when used to judge local efficacy. If there is residual or local progression of hepatocellular carcinoma after ablation, ultrasonography may show high enhancement, but the duration is only a few seconds, so if the lesion is large, it may not be too late to scan the area and the diagnosis may be missed. Three-dimensional ultrasonography can obtain images of the entire area of interest within seconds, and can be viewed from different angles after reconstruction processing. Therefore, 3D ultrasonography can theoretically improve the ability to determine local efficacy.
The concept of precise ablation of hepatocellular carcinoma is of great significance in guiding clinicians to change their concepts, strictly abide by the ablation operation specification and improve the ablation technology level. It is the direction that ablation technology must take after more than 20 years of development, and it is also bound to enable more liver cancer patients to benefit from this minimally invasive, efficacious and precise treatment.