**1. Introduction**

Laser interstitial thermal therapy (LITT) is a minimally invasive ablative technique that continues to gain popularity in a variety of domains of neurosurgery including neuro-oncology, epilepsy surgery, spine oncology and degenerative spine surgery, as well as chronic pain syndromes. In neuro-oncology, laser ablation is used for treatment of a variety of intracranial neoplasms but used most frequently for treatment of recurrent brain metastases and radiation necrosis, as well as treatment of recurrent and newly diagnosed, difficult to access gliomas and other deep-seated tumors. The procedure involves placing a laser catheter

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

under stereotactic guidance, and the size of the lesion produced as a result of laser ablation is monitored using MR thermography in real time. The minimal invasiveness of the procedure makes it a good choice in patients that cannot tolerate a large operation due to either burden of disease or poor performance status.

remission, whereas the other 50% had no response to elevated temperatures [15]. The threshold temperature at which irreversible damage occurs is different across species. While cell cycle arrest and increased cell death in rodent cell lines occurs at 43°C, in human cell lines

Laser Interstitial Thermal Therapy in Glioblastoma http://dx.doi.org/10.5772/intechopen.77078 189

The mechanism by which mild hyperthermia induces damage to cancer cells may involve activation of apoptosis pathways in a temperature dependent fashion, resulting in changes of expression of heat shock proteins such as HSP 27 and 72. The latter display antitumor properties by initiating immunologic response resulting in activation of natural killer cells directed

Laser interstitial therapy is an ablative technique that results in tissue destruction as a result of heating. Photons produced by the laser light are absorbed by the surrounding tissues causing excitation and release of excess energy as heat [18]. Once the critical thermal threshold is reached, protein denaturation and irreversible tissue coagulation ensues resulting in perma-

The first lasers that were attempted for tissue ablation were ruby-based [19]. The amount of energy and thus tissue damage produced by these lasers was difficult to control. In 1983, Bown et al. first described the use of the neodymium-doped yttrium aluminum garnet (Nd:YAG) laser for tissue ablation [20]. At present, two commercially available FDA-approved systems are available for use in neurosurgery in the United States: The NeuroBlate System (Monteris Medical, Plymouth, MN) and the Visualase Thermal Therapy System (Medtronic Inc., Minneapolis, MN). Laser ablation uses laser energy in the near-infrared range where the

main tissue interactions are heating and coagulation (as opposed to cutting for the CO<sup>2</sup>

Both commercial laser ablation systems use diode lasers—one at the Nd:YAG wavelength (1064 nm) and the other at 980 nm. Although there have been claims that one is superior to the other, these are not founded in fact [21]. Lasers in this near-infrared range only penetrate a few millimeters into brain tissue. This heat is then propagated by conduction to allow for

The wavelength of the laser light is what determines the efficiency of energy transfer to the tissues and, as a result, the volume of the lesion produced. Furthermore, the duration of tissue exposure to the laser light affects the amount of energy transferred and thus the amount of heating produced, with longer duration of exposure resulting in higher temperatures achieved in exposed tissues [22–24]. The design of the optical fiber and the laser catheter further affects the properties of the laser. Initially, lasers had to be used at very low power (1–5 W) to avoid excessive heating that results in tissue charring. Improvement in laser catheter design with the development of cooling mechanisms allowed use of higher power while still protecting nearby tissues. This also provides a non-stick catheter surface that allows the laser probe to glide easily through tissues. Current cooling systems employed in laser probe

, or a continuous flow of saline through a sheath

laser).

that threshold is at 41°C [16].

against tumor cells [17].

nent tissue damage.

**2.2. Principles of laser thermal therapy**

ablation radii that may extend up to 15–20 mm.

design use either cooled gas system with CO2

surrounding the optic fiber.

Glioblastoma is a diffuse primary brain neoplasm with poor prognosis. The invasive nature and malignant potential of this tumor make its treatment a challenge. The current standard of care management paradigm consists of a multidisciplinary approach by combining maximal safe tumor resection with subsequent chemotherapy and radiation [1]. Despite maximal treatment, survival rates of glioblastoma remain poor with median survival of 14–16 months. Recent evidence indicates, however, that the extent of resection of high-grade gliomas correlates with patient survival [2–6]. In a similar sense, laser ablation can provide effective tumor cytoreduction to maximize the effectiveness of adjuvant treatments. Furthermore, there is promising evidence that hyperthermia may have additional synergistic effects with radiation, as well as disrupt blood-brain barrier (BBB) and thus facilitate chemotherapy delivery to target tissues [7, 8].

The following chapter will focus on describing the principles of laser ablation and the equipment used to deliver laser energy to brain tumors, as well as discussing current evidence for the use of laser thermal therapy in management of high-grade gliomas.
