Ablative therapies

Ablative Therapies

Minimally invasive ablative procedures guided by imaging, utilizing needle-like applicators, encompass both thermal techniques (such as radiofrequency, microwave, laser, and cryoablation) and nonthermal methods (like chemical ablation and irreversible electroporation). These advanced treatments have garnered significant attention and widespread clinical acceptance, proving effective in addressing focal malignancies across various tumor types and tissues, including primary and secondary cancers in the liver, kidney, lung, and bone. Although focal therapies may have limitations in treating specific tumor sizes and types, researchers have demonstrated success by combining percutaneous procedures with other cancer treatment approaches like chemotherapy, radiation therapy, and transcatheter arterial therapy in various studies.

Type and Mechanism of Action:

Type	Example	Mechanism of action
Chemical	Ethanol, Acetic Acid	1. Destroys tissue by two primary mechanisms: (a) Immediate dehydration of the cytoplasm leads to protein denaturation and consequent coagulation necrosis (b) Necrosis of the vascular endothelium causes platelet aggregation resulting in vascular thrombosis and ischemic tissue necrosis
Thermal (HyperThermic)	Radiofrequency Ablation	1. Electrical current from the generator oscillates between electrodes (Interstitial and Dispersive electrodes) through ion channels present in most biologic tissues 2. Tissue are imperfect conductors of electricity (they have electrical impedance), so current flow leads to frictional agitation at the ionic level and heat generation, known as the Joule effect. 3. Ablative heating leads to tissue dehydration and water vaporization, which cause dramatic increases in circuit impedance.
Thermal (HyperThermic)	Microwave Ablation	1. Microwave heating is produced as a result of dielectric hysteresis (rotating dipoles), which differs from the Joule heating mechanism of RF ablation. 2. When electromagnetic energy is applied to tissue, some of the energy is used to force molecules with an intrinsic dipole moment (e.g., water) to continuously realign with the applied field. 3. This rotation of molecules represents an increase in kinetic energy and, hence, an elevation in local tissue temperatures.
Thermal	CryoAblation	Joule Thomson Effect - Argon and Helium gases are used (a) Freezing cycle - 10 minutes (each) - Faster freezing leads to formation of intracellular ice which causes direct damage to cell membrane and organelles. Slower freezing leads to formation of extracellular ice which changes osmolarity and leads to cell dehydration and cell death. (b) Thawing cycle - 8 minutes (each) Melting of extracellular ice decreases the osmolarity and leads to cell swelling and bursting of cell (c) Delayed phase - Apoptosis
Non-thermal injury	Irreversible electroporation	1. Utilizing high voltage (up to a maximum of 3,000 volts) with brief microsecond pulse durations (ranging from 70 to 90 microseconds) to initiate cell membrane permeability, consequently triggering a gradual and extended process of cellular demise. 2. Immune mediated cell death enables the efficient removal of cellular debris while causing minimal disruption to the surrounding essential tissue structures.

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