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LITT, also known as laser ablation, can be characterized as thermal coagulation of the target tissue caused by conversion of the absorbed energy of the more or less prolonged laser photo-irradiation into heat [7]. In comparison with other thermal sources, lasers have definite advantages for the application of local hyperthermia in the management of brain diseases. RF energy cannot be accurately focused and creates excessive and irregular heating of the superficial tissues. Microwaves are associated with significant gradients of temperature, which may result in dangerous consequences, and have profound loss of tissue penetration at frequencies above 1,000 MHz. HIFU also has restricted thermal penetration. Use of a laser beam helps to avoid these drawbacks and limitations. Photo-irradiation applied with low power (0.5–5 W) during a sufficiently long exposure time (40–100 s) delivers homogeneously distributed energy, and induces local hyperthermia with easy spatial and temporal control. Moreover, in comparison to such techniques as cryodestruction or RF ablation, LITT produces a much faster effect and may create a sharper border of the affected area. Additionally, it is highly compatible with MRI, thus guidance with MR thermometry allows precise real-time monitoring during the procedure and direct visual feedback about 3-dimensional (3D) distribution of the induced thermal tissue damage, its size and its severity; this provides an opportunity to avoid injury to functionally important brain structures.

Induced effects of LITT are realized through several subsequent stages including transmission, absorption, and degradation of the laser photo-irradiation energy within the targeted tissue, and its conversion into heat, causing a local biological reaction [7, 8]. A simple and widely used mathematical algorithm for determination of the heating duration leading to thermal injury during LITT is based on the Arrhenius model of chemical reaction rates: t = A exp(E/R [T+273]), which reflects time (t) required to produce cell death at a constant temperature (T at °C) and contains two constants, namely activation energy (E) and pre-exponential factor (A). The latter parameters may vary in different biological tissues and have not been precisely defined in humans [9], but experimental studies have demonstrated that E is relatively large and consequently, t decreases very rapidly with increase of T.

Depending on the intensity of the laser beam and distance from the fiber tip the rise of temperature results in tissue destruction and protein denaturation. Heat diffusion strongly depends on local perfusion and spreads through a large volume of normal brain parenchyma [10]. In poorly vascularized low-grade gliomas (LGG), an efficient thermal diffusion reaches up to 15–20 mm from the laser fiber tip, while it is relatively lower in cases of highly vascularized high-grade gliomas (HGG) and other malignant neoplasms.