Of particular interest in this growing field of minimally invasive ablation therapies are the thermal ablation methods.
Heat has been known for a long time to be a potent way to destroy tissues as burns testifies everyday. It suffice to raise the temperature within a tissue above a lethal threshold (>60°C) to ensure cellular death within seconds in the target tissue through coagulation. The physical means to raise the temperature within a tissue are numerous and several thermal ablation techniques have been developed, tested and evaluated.
Radio Frequency Ablation
The most widely used thermal ablation technique is based on the insertion in the tumor of a needle like applicator. The applicator is connected to a RF current generator and the return circuit is usually made of a ground pad attached to the leg of the patient. It is called radiofrequency ablation (RFA) and is commonly used in the case of liver, lung and bone tumors. The heating is produced by the displacement of the ions around the tip of the applicator needle.
Focused Ultrasound Ablation
Ultrasound ablation also called Focused Ultrasound Surgery (FUS) or High Intensity Focused Ultrasound (HIFU) is probably one of the most promising technique due to its totally non invasive nature. The principle is rather simple: a powerful ultrasound generating device called a transducer, located outside of the patient, body focuses ultrasound at the tumor location to rapidly raise the temperature at the focal point above the lethal threshold.
Laser is also used as an energy source to heat tissues. An optic fiber with a diffuser tip is inserted in the tumor and the infrared laser raises the temperature around the diffuser. Laser ablation was historically the first to be widely used but suffers from a limited range of heating away from the optic fiber which limit its use to very small tumors.
Microwave applied with small needle like antennas can also be used to heat a target tissue. Use of this technique has so far been rather limited partly due to the availability of microwave ablation devices.