Interstitial laser irradiation of cerebral gliomas – Neurobiological background , technique and typical results

Background: The most common type of primary brain tumors are gliomas. For patients unsuitable for open microsurgery having been treated by radiochemotherapy, laser irradiation has proven to be an alternative palliative option. From summer 1997 until winter 2006 we performed about 60 laser-interstitial thermotherapy (LITT) treatments, starting with patients with large recurrent tumors who had no other therapeutic option. In the present article we report about the neurobiological background, the technique and our experience with LITT of cerebral gliomas. Materials and method: For laser irradiation we used a specially designed light guide (LITT standard applicator; Trumpf Medizintechnik, Umkirch, Germany). The tip of this light guide is a special optical diffuser which is characterized by a homogeneous spherical or ellipsoid emission profile. The light guide was introduced into an appropriate protective sheath (Somatex, Teltow, Germany). For the laser light source, we used a continuous wave 1064-nm Nd:YAG laser (mediLas fibertom 4060 N; Dornier MedTech, Weßling, Germany). Laser irradiation was performed under general anesthesia in a 0.5 T open configuration magnetic resonance (MR) system (Signa SP; General Electric, Milwaukee, WI, USA). Usually, the tip of the light guide was positioned in the center of the tumor using the built-in localization system (Flashpoint 3000; IGT, Boulder, CO, USA) in combination, where appropriate, with a specially designed navigation system (LocaliteTM, Bonn, Germany). The position of the light guide was then controlled using multiplanar reconstructions of T1-weighted sequences. For near real-time control, temperature monitoring was performed using an experimental software package based on the temperature-dependent shift of the MR signal. Laser irradiation was ceased when the temperature monitoring revealed a steady state temperature profile within the heated tissue. Since 2008 we have used traditional stereotactic targeting and methionine positron emission tomography/computed tomography (MET-PET/CT) instead of the ‘open’ MR system for planning and follow-up in LITT of brain tumors. Results: We started the LITT treatment of gliomas in the early 1990s (benign gliomas in eloquent regions/not suitable for surgery). In 1997 we started to treat patients with recurrent gliobastomas/anaplastic gliomas. All of these patients had an increased survival in comparison to the natural course of recurrent glioblastomas. There were no procedure-related deaths or permanent neurological deficits. Two factors seem to be important for the overall success of the LITT procedure: 1) an early enrollment in the LITT therapy after diagnosis of a tumor recurrence, and 2) a corresponding smaller tumor mass at the beginning of the therapy. Conclusion: Cytoreduction by laser irradiation seems to be a promising option for patients suffering from gliomas.