Interstitial photodynamic therapy for malignant gliomas: the Munich experience

5-aminolevulinic acid (5-ALA) mediated interstitial photodynamic therapy (iPDT) is undergoing clinical trials for the treatment of malignant gliomas. 5-ALA iPDT is based on the creation of reactive oxygen species (ROS) via excitation of 5-ALA mediated protoporphyrin IX (PpIX) in the tumor cells and causing a phototoxic reaction. After iPDT local chemo-radiation is performed as adjuvant therapy. 16 newly diagnosed glioblastomas and 44 malignant glioma recurrences treated with 5-ALA iPDT in Munich were retrospectively analyzed for treatment outcome, spectral online monitoring and changes in the MRI. iPDT for newly diagnosed glioblastomas showed a median overall survival (OS) of 28 months, 16.4 months progression free survival (PFS), respectively. 43.8% patients with newly diagnosed glioblastoma experienced a long term PFS > 24 months. In addition, the methylation of the MGMT promotor showed to be a prognostic factor for prolonged survival (p=0.04). In case of recurrent malignant gliomas PFS after iPDT was 7.1 months with 25% >24 months survival after iPDT (17.9% PFS > 24 months). Analysis of spectral online monitoring showed that a measured decrease of the laser light transmission between the cylindrical diffuser fibers, used for the irradiation, can be associated with silent hemorrhages visible in terms of T1-hyperintensity in the MRI after iPDT. Overall 5-ALA iPDT is a promising tool for the treatment of glioblastomas and other malignant gliomas with prolonged survival and minimally invasive surgery.