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Ablation for Interventional Radiologists: Modalities for Tumor Treatment under CT Guidance



Interventional radiology has advanced significantly in the field of tumor treatment, with interventional oncology (IO) becoming the so-called fourth pillar in cancer care. Ablation techniques are a cornerstone of IO, and favored for tumor treatment because they are an effective and minimally invasive option. Among the various modalities available, thermal ablation (including radiofrequency ablation, microwave ablation, and cryoablation) and irreversible electroporation (IRE) are commonly performed under CT guidance. In this article, we explore the key differences between these ablation techniques, discussing their fundamental principles, highlighting their advantages and limitations, and identifying their specific applications. Let’s get started!


Radiofrequency Ablation (RFA)


Radiofrequency Ablation (RFA) operates on the principle of using high-frequency alternating current to generate heat, which is carefully directed at the targeted tissue1. This method boasts precise and controlled tissue destruction, making it a common choice for cardiac and hepatic procedures. It is preferred for its ability to minimize harm to surrounding healthy tissue. However, it may require multiple sessions for complete ablation, possesses limited depth of penetration, and carries the risk of collateral thermal injury. RFA is typically effective within ablation zones ranging from 2-5 cm, although tissue conductivity, impedance, and blood perfusion (together known as a ‘heat sink effect’) can influence the impact, and the exact shape and size of the ablation zone can be unpredictable2.


RFA is preferred for its ability to minimize harm to surrounding healthy tissue.



Cryoablation


Cryoablation employs extreme cold, with temperatures ranging from -40°C to -85°C, to freeze and destroy targeted tissue. This technique offers several advantages, including being well tolerated under conscious sedation due to the anesthetic effect of tissue cooling3, precise control over the ablation zone, and the ability to perform it as an outpatient procedure4. If the tumor is near critical structures, such as major blood vessels, bile ducts, or the gastrointestinal tract, cryoablation becomes a preferred choice. Cryoablation's freezing effect creates a "safety zone" that helps protect adjacent organs from thermal injury during the procedure5.

Additionally, cryoablation allows for real-time visualization of the ablation zone due to the formation of an ice ball6. Careful placement of probes allows for the ablation zone to precisely match the shape of the lesion3. However, it demands specialized equipment, the availability of large quantities of gas (which can be expensive), and is a slower ablation process compared to RFA6. Furthermore, there is a potential for causing systemic inflammatory response syndrome and bleeding complications due to the absence of cautery effects7. Cryoablation is notably effective in treating renal cell carcinoma (RCC), hepatocellular carcinoma (HCC)8, fibroadenomas, prostate tumors, and bone cancers9.


Microwave Ablation


Microwave ablation harnesses the power of electromagnetic microwaves to generate heat through friction, resulting in the rapid destruction of targeted tissue10. Because microwave ablation primarily agitates water molecules, organs with high water content, such as the liver or kidney are particularly suitable for treatment11. This technique offers several advantages, such as shorter procedure times, good efficacy in treating liver and lung tumors, good depth of penetration, suitability for large tumors and those situated near many or large vessels, and comparable effectiveness to tumor resection in liver, lung, and kidney cases12. However, it does carry risks, including the potential for overheating adjacent tissues, and has limited suitability for smaller tumors.


Microwave ablation offers several advantages, such as shorter procedure times, good efficacy in treating liver and lung tumors, good depth of penetration, [and] suitability for large tumors...


Irreversible Electroporation

Irreversible Electroporation (IRE) operates on the principle of inducing electrical pulses that disrupt the homeostatic equilibrium of cells, ultimately leading to cell death. Multiple probes, usually between 2 to 6, are placed in parallel to create the desired ablation zone.


It is particularly well-suited for treating tumors located near large vessels and ducts13. IRE is especially effective in treating specific cases, including prostate cancer and unresectable advanced pancreatic cancer. IRE procedures require general anesthesia to ensure patient comfort during the intervention, which could cause complications or limit feasibility for certain patients. Due to the relatively recent identification of IRE as a tumor treatment modality, much is still unknown about the optimal use and limitations of IRE14.


Choosing the Right Technique

  • Depth and Size: Consider the depth and size of the target tissue. For superficial lesions or small tumors, techniques like cryoablation may be suitable. For deeper or larger targets, microwave or RFA might be more appropriate.

  • Precision: If precision and minimal damage to surrounding tissue are crucial, techniques like RFA and microwave ablation are preferred.

  • Patient Factors: Take into account the patient's overall health, comfort, and any contraindications to specific techniques.

  • Equipment and Expertise: Ensure that the necessary equipment and expertise are available for the chosen technique.

  • Navigation: Enhance the efficacy and speed of the procedure by choosing a navigation solution that will deliver the antenna directly to the target and keep it there during a long ablation. Systems with low overhead and the ability to hold probes in place, like the Cube Navigation System, are especially advantageous.

Each of these ablation techniques—Radiofrequency Ablation (RFA), Cryoablation, Microwave Ablation, and Irreversible Electroporation (IRE)—offers unique advantages and has specific applications in medical procedures, particularly in the treatment of tumors. The choice of technique depends on factors such as the location and size of the tumor, the patient's overall health, and the expertise of the medical team. Understanding the principles, advantages, and limitations of these techniques is crucial for informed decision-making in the field of medical ablation. Always check guidelines issued by recognized radiology and IO societies for specifics on which ablation modality is appropriate for the patient.


A navigation solution which supports each of these ablation modalities is critical to achieving accurate antenna placement, allowing the user to maximize the therapeutic effect while minimizing damage to healthy surrounding tissues.


Perhaps most importantly, a navigation solution which supports each of these ablation modalities is critical to achieving accurate antenna placement, allowing the user to maximize the therapeutic effect while minimizing damage to healthy surrounding tissues. The Cube Navigation System, compatible with ablation antennas of all types (10-20G), ensures that interventional radiologists have the flexibility to choose the most suitable ablation modality for each patient and tumor scenario. With the ability to hold the antenna securely in place during the procedure, maintaining the desired position and ensuring consistent energy delivery is easy, contributing to the success of the ablation therapy.




References

1. McDermott S, Gervais DA. Radiofrequency ablation of liver tumors. Semin Intervent Radiol. 2013;30(1):49-55. doi:10.1055/S-0033-1333653

2. Ablation Modalities in Interventional Oncology - Endovascular Today. Accessed September 26, 2023. https://evtoday.com/articles/2021-oct/ablation-modalities-in-interventional-oncology

3. Moschovaki-Zeiger O. Cryoablation of a soft tissue metastasis . Highlights in IR. Published online February 2023.

4. Niu LZ, Li JL, Xu KC. Percutaneous Cryoablation for Liver Cancer. J Clin Transl Hepatol. 2014;2(3):182. doi:10.14218/JCTH.2014.00017

5. Cryosurgical effects on growing vessels - PubMed. Accessed September 26, 2023. https://pubmed.ncbi.nlm.nih.gov/10399979/

6. Erinjeri JP, Clark TWI. Cryoablation: Mechanism of action and devices. Journal of Vascular and Interventional Radiology. 2010;21(SUPPL. 8). doi:10.1016/J.JVIR.2009.12.403

7. Chapman WC, Debelak JP, Blackwell TS, et al. Hepatic cryoablation-induced acute lung injury: Pulmonary hemodynamic and permeability effects in a sheep model. Archives of Surgery. 2000;135(6):667-673. doi:10.1001/ARCHSURG.135.6.667

8. Song KD. Percutaneous cryoablation for hepatocellular carcinoma. Clin Mol Hepatol. 2016;22(4):509-515. doi:10.3350/CMH.2016.0079

9. Jennings JW, Prologo JD, Garnon J, et al. Cryoablation for palliation of painful bone metastases: The motion multicenter study. Radiol Imaging Cancer. 2021;3(2). doi:10.1148/RYCAN.2021200101

10. Vogl TJ, Nour-Eldin NEA, Hammerstingl RM, Panahi B, Naguib NNN. Microwave Ablation (MWA): Basics, Technique and Results in Primary and Metastatic Liver Neoplasms - Review Article. RoFo Fortschritte auf dem Gebiet der Rontgenstrahlen und der Bildgebenden Verfahren. 2017;189(11):1055-1066. doi:10.1055/S-0043-117410

11. Knavel EM, Brace CL. Tumor Ablation: Common Modalities and General Practices. Tech Vasc Interv Radiol. 2013;16(4):192. doi:10.1053/J.TVIR.2013.08.002

12. Hernández JI, Cepeda MFJ, Valdés F, Guerrero GD. Microwave ablation: State-of-the-art review. Onco Targets Ther. 2015;8:1627-1632. doi:10.2147/OTT.S81734

13. Aycock KN, Davalos R V. Irreversible Electroporation: Background, Theory, and Review of Recent Developments in Clinical Oncology. Bioelectricity. 2019;1(4):214-234. doi:10.1089/BIOE.2019.0029

14. Ong S, Leonardo M, Chengodu T, Bagguley D, Lawrentschuk N. Irreversible electroporation for prostate cancer. Life. 2021;11(6). doi:10.3390/LIFE11060490

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