C6 Interstitial Photodynamic Therapy

Interstitial photodynamic therapy based on the photosensitizer protoporphyrin IX (PpIX), induced by administration of 5-aminolevulinic acid (5-ALA iPDT), is an emerging treatment approach for malignant gliomas. After minimally invasive introduction of light applicators, laser light is delivered into the tumor region. The laser light activates the photosensitizer PpIX that selectively accumulates in the tumor cells. By interaction of the activated photosensitizer with intracellular oxgen, reactive oxygen species (ROS) are generated that destroy the tumor, cells while healthy tissue is largely preserved.

For treatment individualization and optimization, knowledge about light and effect distribution within the tissue is important, i.e. about optical tissue properties, photosensitizer concentration, and changes thereof during treatment. For this purpose, online monitoring procedures are established and further developed, to assess the distribution of laser light and photosensitizer fluorescence within the tissue. The obtained optical signals are analysed on the basis of MRI and compared to Monte Carlo simulations of light distribution in tissue (see figure for example).

In addition, medical imaging data of the brain are analysed with respect to suitable surrogate markers for the estimation of optical tissue properties and with respect to signatures for iPDT-induced changes. Comparing with treatment outcome, a relation to treatment light delivery is investigated.