Interstitial photodynamic therapy of nonresectable malignant glioma recurrences using 5-aminolevulinic acid induced protoporphyrin IX

Background and Objective: Limited knowledge of the light and temperature distribution within the target volume in combination with non-selective accumulation of the applied photosensitizers (PS) has hampered the clinical relevance of interstitial photodynamic therapy (iPDT) for treatment of malignant glioma patients. The current pilot study focused on the development and the clinical implementation of an accurate and reproducible irradiation scheme for iPDT using 5-aminolevulinic acid (5-ALA) induced protoporphyrin IX (PPIX) as a selectively working PS. Study Design/Materials and Methods: Monte Carlo simulations of fluence rate and heat transport simulations were performed using the optical properties of normal brain tissue infiltrated by tumor cells (absorption coefficient mu(a) = 0.2 cm(-1), reduced scattering coefficient: mu'(s) = 20 cm(-1)). A modified 3-D treatment-planning software was used to calculate both, the treatment-volume and the exact position of the light diffusers within the lesion. The feasibility and the risk of iPDT were tested in 10 patients with small and circumscribed recurrent malignant gliomas. Results: The optimum distance between the implanted light diffusers was determined to be 9 mm with regard to both fluence rate and temperature distribution. For this distance a temperature increase above 42 degrees C was not expected to occur. Up to six cylindrical light diffusers were stereotactically implanted to achieve a complete irradiation of the tumor volume, which was possible in every single patient (mean tumor volume: 5.9 cm(3)). The total applied light fluence was between 4,320 J and 11,520 J. Side effectsof iPDT were not observed. Median survival was 15 months. Conclusion: 5-ALA iPDT in combination with a 3-D treatment-planning (which was based on optical and thermal simulations) is a safe and feasible treatment modality. The clinical impact of these findings deserves further prospective evaluation.