The development of imaging equipment and technology has prolonged the doctor’s vision so that we can precisely see the internal structure of the human body without opening the human tissue through surgery; while the development of medical devices has prolonged the doctor’s hands so that we can accurately reach the lesion site for treatment without exposing the human tissue and organs. In the new century, minimally invasive interventional treatment of tumors under imaging guidance has been developing rapidly in the global medical field because of its unique advantages,
The main feature is to destroy the tumor in situ and protect the body to the maximum extent. Minimally invasive imaging-guided interventional therapy can be divided into two categories: vascular and non-vascular; the main components of vascular interventional therapy are local perfusion chemotherapy and embolization of tumors through selective intubation of blood vessels, while the main components of non-vascular intervention are ablation of tumors through percutaneous puncture and implantation of radioactive particles. Chemoablation is the direct injection of ablative agent into tumor by percutaneous puncture of tumor tissue under the guidance of imaging equipment to achieve in situ tumor inactivation. Chemoablation is suitable for primary and metastatic tumors in various parts of the body, such as benign and malignant tumors of adrenal gland, primary liver cancer with lack of blood supply, metastatic liver cancer, lung cancer, pelvic tumors, etc., or incomplete filling of iodine oil and lymph node metastasis in the lesion after TACE of liver cancer. Commonly used ablative agents include tumor cytotoxic agents (various chemotherapeutic drugs), protein coagulants, etc. 1.Tumor cytotoxic agent: The commonly used method is to inject chemotherapy drugs proportioned according to the cytological type of tumor and a small amount of iodized oil into the tumor or metastatic lymph nodes percutaneously, so that the anti-tumor drugs are released slowly and directly kill the tumor cells in the tumor, which improves the local chemotherapy concentration and reduces the toxic damage of chemotherapy drugs to the patient’s whole body. The disadvantage is that the precise dosage and release time of the drug in the tumor are not easy to grasp, and repeated injections are often required. Many scholars have attempted to prepare slow-release microsphere loads of various chemotherapeutic drugs for injection into the tumor under ultrasound, CT or MRI guidance.
This increases the release time and smoothness of the drug, and reduces the peak concentration of the drug in the blood and the number of doses compared with systemic dosing. Various ratios of drug slow release microspheres are still under research and development. 2, protein coagulant: commonly used are anhydrous ethanol, glacial acetic acid, etc.. Its principle is to make tumor cells coagulate, cytoplasm dehydration, tumor vascular epithelial cell necrosis, small blood vessel thrombosis to make tumor tissue ischemic necrosis. For smaller tumors, the anhydrous ethanol can easily diffuse and make the tumor necrosis more complete due to the uniformity of the tumor tissue structure, while for larger tumors, the diffusion of the ablative agent is limited due to the presence of mixed components and fibrous separation in the tumor. The diffusivity and permeability of glacial acetic acid are greater than that of anhydrous alcohol, which can accelerate coagulative necrosis by directly destroying cell membranes, and the histological changes after injection are faster, earlier, more obvious and complete than those of anhydrous alcohol. The basic principle of hot saline or thermal contrast agent is to inject into the tumor to rapidly increase the intra-tumor temperature to achieve ablation. Ohnishi used hot saline for experimental treatment in 1993 to obtain satisfactory tumor necrosis effect, and then domestic scholars reported satisfactory clinical effect, but the clinical application showed that the internal temperature of tumor was difficult to control and the necrosis was not uniform. Physical ablation is the process of necrosis of a tumor through cold or heat by puncturing the lesion under image guidance. Physical ablation is also divided into thermal ablation and cold ablation, and the commonly used thermal ablation methods are radiofrequency ablation, microwave ablation and laser ablation, etc. 1.Thermal ablation
ablation): Tumor cells are very sensitive to temperature and cannot tolerate temperature above 60℃, and above 70℃, they will all apoptosis. The internal temperature of whole body thermal therapy cannot exceed 40℃, so the therapeutic effect on tumor is limited. In situ inactivation of tumor can be achieved by generating high temperature inside the tumor through physics. Among the thermal ablation treatments, radiofrequency ablation (RFA) is the most popular treatment.
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Ablation (RFA) is the most widely used. Its basic principle is to introduce high frequency oscillating current into the tumor tissue through the ablation electrode, so that the ions and polarized molecules in the local tissue oscillate rapidly with the alternating direction of the current, resulting in frictional heat generation in the tissue. When the local temperature reaches 50℃, it lasts for 4-6 min.
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When the temperature exceeds 70℃, the cells die immediately; when the temperature reaches 100℃, the cell membrane is dissolved, the intercellular water evaporates, and the tissue disintegrates and carbonizes. The ablation area of tumor is spherical or oval, and the maximum diameter of ablation at one time can be up to 55 mm at the current multi-needle ablation electrode. Radiofrequency thermal ablation as a minimally invasive treatment technology has been widely used in the treatment of liver, kidney, prostate and other substantial organ tumors, and has achieved ideal efficacy. 2.Cryoablation: The recent cryotherapy device argon helium knife is using Joule-Thomson effect, using room temperature high pressure argon gas cooling, the lowest temperature at the tip part can reach -185℃, high pressure helium gas rewarming, the temperature can reach 70℃. Tumor necrosis is accelerated by cycles such as freeze-retemperature. The commonly used probe is an ultra-fine probe with a diameter of 1.47 mm, which allows cryoablation of larger lesions through a combination of multiple needles. The principle of cryogenic freezing is the formation of ice crystals within the interstitial cell. Changes in electrolytes and osmotic pressure inside and outside the cell lead to cell dehydration, damage to the cell membrane, which in turn leads to intracellular ice crystal formation and cell degeneration and necrosis. The intima and basement membranes of microarteries and microvenules swell and break during cryoablation, which leads to extensive thrombosis within the local microcirculation upon rewarming, further aggravating tissue hypoxia and promoting tissue necrosis. Cryoablation is currently the best treatment for larger tumors (>3 cm in diameter).
It has no toxic side effects and the long-term follow-up results prove that the survival rate is high. 3.Laser ablation: This technique is performed through a 0.4 mm diameter fiber in the lesion.
Laser ablation: This technique is performed by a 0.4 mm diameter optical fiber that emits/scatters laser light in the lesion and transforms it into heat energy, causing coagulation and necrosis of tumor cells without damaging the surrounding tissues. The laser energy can cause spherical coagulation necrosis around the laser beam. The size of laser ablation is not only related to its energy accumulation, but also depends on the blood supply of the tumor and the vasodilatory response of the surrounding normal tissues. The efficacy of LITT treatment depends on the precise position of the laser probe and the temperature change of the local tumor tissue. Ultrasound, CT, magnetic resonance imaging (MRI), CT-PET and other imaging methods can monitor the range of action of LITT. In recent years, MRI is multi-planar oriented and can show temperature changes and coagulation necrosis, which makes the operation process more precise. Due to equipment limitations, this technique has not been widely carried out. Radioactive particle implantation is an advanced minimally invasive treatment method for malignant tumors, which is a kind of brachytherapy. It is a new technology of minimally invasive in vivo radiotherapy for malignant tumors, which fully combines advanced image guidance equipment and in vivo brachytherapy technology. The clinical efficacy of low-energy radiation seed source is derived from the interaction between the excited ion stream and the tissue organ, thus irradiating the tumor site at close range. DNA is the key target of radiation action on cells, and radiation irradiation causes DNA strand breakage, which makes tumor cells lose the ability to reproduce. Studies have shown that during the tumor growth process, the late stage of DNA synthesis and mitotic phase in the reproductive cycle are the most sensitive to radiation, while the cells in the quiescent phase are the least sensitive to radiation. In vitro radiotherapy can only treat cells in a small part of the tumor reproduction cycle in short time. Although the energy of radiation produced by implanting radioactive particles between tumor tissues is not large, it can continuously act on tumor cells and kill tumor stem cells uninterruptedly, and after sufficient dose and half-life, it can make all tumor cells lose their reproduction ability and achieve complete treatment effect. Preferred application of various technologies in tumor treatment Various ablation methods have different advantages and disadvantages, and one ablation method should never be used to treat all tumors in clinical work. For example, physical ablation of enlarged lymph nodes in retroperitoneal, pelvic or mediastinal metastases is very difficult and risky due to the complex structure and close arrangement of adjacent lesions, while chemical ablation is easy to implement and can achieve better efficacy, but physical ablation is significantly more efficient than chemical ablation in substantial organs. In cases of cirrhosis combined with hepatocellular carcinoma, if the patient’s platelet and coagulation indexes are low, thermal ablation with good hemostatic effect should be chosen as much as possible. In the ablation of non-substantial organ tumors such as lung cancer and bone metastases, cryoablation is well tolerated by patients and the scope of ablation can be easily controlled, etc. Ar-He knife cold ablation should be chosen. When the tumor is large, poorly defined and invades adjacent structures, radioactive particle implantation should be chosen. As an excellent imaging-guided minimally invasive therapist, he/she should master at least 4 kinds of local tumor treatment techniques in order to choose the best method or combination of treatment methods in minimally invasive tumor treatment flexibly. Image-guided minimally invasive percutaneous interventional techniques have shown impressive application prospects for the treatment of malignant tumors, and their combined application can improve the cure rate and long-term survival rate of tumors. The principles of choosing local minimally invasive treatment methods for tumors are: economical, minimally invasive, safe and efficient.