Thermal Ablation Techniques- Overview

Introduction

Thermal ablation is a procedure for the eradication of tissue through the application of either excessive hyperthermia, characterized by raised tissue temperatures, or hypothermia, characterized by reduced tissue temperatures. The alteration in temperature is localized within a specific region, including the tumor.

What Is the Purpose of Thermal Ablation?

• The primary goal of thermal tumor ablation is closely related to that of surgical intervention, which is the complete eradication of the tumor together with a surrounding margin of healthy tissue.

• The process of surgical removal involves the physical excision of tissue, while thermal ablation entails the destruction of tissue followed by gradual absorption by the body for several months.

• Similar to surgical procedures, thermal ablation techniques can be executed through many approaches, such as open, laparoscopic (minimally invasive surgery), or endoscopic (a noninvasive procedure employed to examine an individual's gastrointestinal tract) methods.

• However, the noninvasive route is the most frequently employed method for thermal ablation. The selection of the technique is frequently influenced by various factors, including the specific characteristics of the tumor, its anatomical placement, the personal preference of the clinician, and the overall health status of the patient.

• While surgical procedures often involve visual inspection and histological assessment of the excised tumor and margins, percutaneous and noninvasive thermal ablation procedures rely solely on imaging guidance. The effectiveness of imaging plays a crucial role in various aspects of medical practice, including the directing of applicators into the target zone, monitoring and verifying treatments, and ensuring appropriate clinical follow-up.

What Are the Advantages of Thermal Ablation?

The advantages include the following:

• Thermal ablation is characterized by the quality of being efficient and prompt in completing nature, with a relatively brief duration of the process and subsequent swift recovery. Chemotherapy can be promptly recommenced in patients requiring this treatment. The duration of postoperative recovery with cryosurgery (a procedure that uses liquid nitrogen or argon gas to produce extremely cold temperatures to kill cancer cells and abnormal tissue) may potentially be shorter compared to that of open surgery.

• Thermal ablation is a more cost-effective alternative compared to other available treatment alternatives.

• Patients have the option of being discharged a few hours following the procedure. Typically, there is no need for overnight stays to manage discomfort.

• Due to the utilization of a minor incision by the medical practitioner to introduce the probe through the skin, the extent of harm caused to healthy tissue is minimized.

What Are the Risks Associated With Thermal Ablation?

The potential hazards or dangers associated with a particular activity include the following:

• Medical intervention that involves the penetration of the skin poses a potential risk of infection. The probability of acquiring an illness that necessitates antibiotic therapy seems to be lower. Additionally, there may be instances of bleeding as a consequence.

• Although physicians make efforts to minimize harm to adjacent tissues through the use of imaging guidance, normal structures can sustain injury. The potential adverse effects of ablation may include discomfort, inflammation of the treated organ, formation of abscesses, or the occurrence of infections, which can vary depending on the specific treatment location.

• There is a possibility of causing complications associated with the administration of procedure drugs, such as anesthesia.

• The process entails the potential exposure to X-ray radiation; the potential risks associated with radiation exposure are insignificant in comparison to the numerous advantages offered by the therapy.

• Patients may experience a condition known as "post-ablation syndrome," characterized by flu-like symptoms that manifest within a period of three to five days following the treatment and typically persist for approximately five days. The illness can last between two and three weeks.

How Does the Technique Function?

The medical practitioner will employ ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI) techniques to facilitate the precise placement of the probe within the tumor.

• Radiofrequency ablation (RFA) uses electrical currents within the spectrum of radiofrequency waves.

• Microwave ablation employs electromagnetic pulses within the microwave frequency spectrum. The transmission of energy through the probe induces thermal energy generation at its distal end.

• The application of heat has been found to effectively eradicate cancer cells and induce the closure of microvasculature, hence reducing the potential for hemorrhage. Over time, the deceased tumor cells are gradually substituted by scar tissue, which undergoes a size reduction.

• Cryoablation employs freezing temperatures to induce tissue destruction, encompassing the eradication of cancerous cells.

• Utilizing image guidance, the medical practitioner introduces a slender cryoprobe, like a wand, through the dermis and into the targeted tissue.

• One or more cryoprobes may be utilized. Either argon or nitrogen gas is introduced into a tube, which subsequently enters the cryoprobe. This process effectively reduces the temperature at the tumor site to extremely low levels. The exceedingly low temperatures induce cryoablation, resulting in the freezing and subsequent destruction of the tumor.

What Is the Process Employed in Implementing the Procedure?

1. Ablation is usually performed in an interventional radiology room or the operating room by a qualified interventional radiologist. A doctor can do outpatient thermal ablation. Some ablation techniques require overnight hospital observation.

2. Doctors and nurses monitor the heart rate, blood pressure, oxygen level, and pulse. A nurse or technologist will put an IV line into the hand or arm to provide a sedative.

3. Imaging will help doctors detect the tumor. A local anesthetic and sterile drape will be applied by the doctor. The region may burn or hurt before numbing.

4. In addition to local anesthesia, doctors may employ intravenous conscious sedation or general anesthesia. They will choose the best anesthesia for the initial examination of the patient.

5. The physician will use imaging to enter the needle through the skin and reach the tumor. The doctor will activate the probe to freeze or burn tumor cells as they may need to adjust the needle electrode or insert many needles into a huge tumor to ablate it. It will help remove tumor tissue.

6. Ablations take ten to 30 minutes, but numerous ablations take longer. The operation takes one to three hours. After the procedure, the doctor will withdraw the needle electrode and apply pressure to stop bleeding. A dressing will cover the skin opening as they need no stitches. The doctor or nurse will remove the IV line before discharge.

What Are the Limitations and Disadvantages Related to Thermal Ablation?

Thermal ablation has a limited ability to eradicate tumor tissue. This problem arises as a result of constraints associated with the existing equipment.

• The progression of technology is expected to enable the treatment of larger tumors. The ablation of microscopic tumors that are not detectable by medical imaging is not feasible. Tumors with dimensions below two to three millimeters (equivalent to approximately 1/10 inch) frequently elude detection using existing imaging techniques.

• The efficacy of cancer treatment may be limited in cases where the disease has metastasized to distant anatomical sites.

• Due to the limitations of current medical imaging techniques, physicians are currently only able to address tumors that are visually detectable on radiologic pictures.

• Consequently, the treatment of microscopic cancer remains unattainable within the existing medical framework.

Conclusion

Image-guided thermal tumor ablation continues to make inroads as a viable treatment option for many focal cancers. Ablation methods based on both heat and cold can be used, and there is no single optimal treatment for all clinical presentations. RF ablation has been the dominant energy for hyperthermic ablation to date but may be supplanted by microwave ablation in the coming years. Laser ablation offers MRI compatibility for precise thermal monitoring, while HIFU offers external energy delivery along with MRI compatibility. Cryoablation is used for many of the same tumors and is more visible than hyperthermic ablations on CT and ultrasound, but may not be suitable for some cancers because of a lack of coagulation. Despite several years’ worth of clinical experience, most ablation systems are in the first or perhaps second generation of development. As technologies for energy delivery continue to improve, expect to hear more about thermal tumor ablation.