**2. Various energy sources of hyperthermia**

Various energy sources including laser, ultrasound, microwaves, and radiofrequency electric current are being investigated as minimally invasive, and potentially non-invasive therapies. There are two types of thermal ablation: radiofrequency (RFA) and microwave. Both are minimally invasive techniques that treat lesions by applying intense heat through a small probe inserted directly into the tumor. Hyperthermia can be either superficial, produced by a microwave generator, or regional, produced by a radiofrequency applicator with multiple antennas, which emanate a deep focalized heating, saving the skin, or interstitial heating. In all these systems the radiations are non-ionizing, in which the energy presents a heterogeneous distribution inside the tissues, depending on their thermal characteristics and on blood perfusion. Radiofrequency ablation (RFA) involves percutaneous or intra-operative insertion of an electrode into a lesion under ultrasonic or CT guidance. Radiofrequency energy is emitted through the electrode and generates heat, leading to coagulative necrosis of the tissue.
