Laser Ablation vs Open Resection for Deep-Seated Tumors

Abstract

Laser interstitial thermal therapy (LITT) is a minimally invasive treatment modality for brain tumors that was first introduced by Bown1 in 1983 and has been revisited and refined as a result of technological advancements since the end of the last century.2,3 The main limitations of this surgical technique (the inability to monitor or predict the extent of ablation, the inability to shape the ablation to conform to the tumor contour, and the lack of a cooling system) have been resolved. LITT is a US Food and Drug Administration–cleared treatment option that can be used to treat recurrent glioblastoma4 and is emerging as a surgical option for upfront treatment of selected patients with malignant glioma and as a treatment for brain metastatic diseases that have failed stereotactic radiosurgery (SRS).5-7 Thermal damage is the basic biological effect of LITT. Laser energy is absorbed by the surrounding tissue, causing excitation and release of thermal energy.8-11 Ultimately, a cascade of events results in cell breakdown and coagulative necrosis of the target tissue. As we move toward a more individualized approach in cancer care based on the biomolecular profile of different types of tumors, we as neurosurgeons should offer surgical options individualized for each group of patients on the basis of their clinical history, performance status, and tumor characteristics (size, location) and the complication profile of different surgical approaches. In a debate at the 2015 Congress of Neurological Surgeons Annual Meeting in New Orleans, Louisiana, we presented the case for laser ablation of deep (ie, >2 cm from the surface of the hemispheres) brain tumors. Besides an introductory background to LITT, the evidence supporting use of LITT in this setting, the inability to use cortical or subcortical mapping, and the potential limitation of tissue sampling for molecular analysis compared with craniotomy were addressed. BACKGROUND OF LITT FOR BRAIN TUMORS As described previously, the major biological effect of LITT is thermal damage.12 Laser photons are emitted and absorbed by surrounding tissue, causing excitation and release of thermal energy, which is transformed to heat and distributed to surrounding tissue through the process of convection and conduction.8-12 The degree of heat penetration into surrounding tissue is determined by the properties of the tissue itself, which determines the extent of thermal ablation.13 Studies have shown that water and hemoglobin content are the main determinants of laser absorption by tissues.14 In addition, the greatest degree of tissue penetration, up to 10 mm, is observed with laser radiation with wavelengths in the near-infrared part of the spectrum.14 The impact on viable tissue is not, however, just a matter of the temperature to which it has been heated; rather, it is the relationship between temperature and time that determines the biologic effect. The Arrhenius equation allows calculation of the probability of cell injury, the type of calculation that computers can do nearly instantaneously. The cascade of cellular events after LITT includes enzyme induction, denaturation of proteins, cellular membrane breakdown, coagulation necrosis, and blood vessel sclerosis.14 It is important to mention that rapid increases in temperature can result in tissue carbonization,15 which prevents adequate laser absorption. Also noteworthy is the fact that overheating will cause tissue vaporization, which could lead to increased intracranial pressure.16 The goal with LITT is to achieve coagulation necrosis of the target volume without provoking carbonization or vaporization of the treated area while preventing injury to surrounding healthy brain. The literature describes 3 zones of particular histological changes around the laser probe during LITT.15 The first zone is the area closest to the tip of the probe and represents the area of greatest tissue damage because of the highest degree of energy absorption.15 Coagu