Interstitial photodynamic therapy (iPDT) is currently being investigated as a light-based treatment option for highly malignant brain tumours (glioblastomas/GBM). To obtain a sufficient irradiation of the tumour, quantitative knowledge about the light propagation in the tissue is required for the light dosimetry calculations underlying the clinical treatment planning. To individualize the light dosimetry calculations, the optical properties of the irradiated tissue need to be determined in-vivo. A novel approach for this purpose is based on the direction-resolved light detection within the tissue, using a rotating optical side-view probe. During measurement, the tissue is irradiated via a separate interstitially placed light applicator, and from the angular dependence of the recorded signal the optical tissue properties are calculated, based on a solution of the radiative transfer equation (RTE). Measurements were performed on liquid tissue phantoms and biological tissue samples. As a result, an over- and underestimation of the calculated optical absorption and scattering coefficients may arise in some situations, but the effective attenuation coefficient remains largely unaffected and corresponds well with literature values.
Thermography is used in many application areas like non-destructive testing, architecture or zoology. Approaches to use thermography for medical diagnostics are usually focused on the detection of tumors. The usefulness and specificity for this purpose has been debated. Nevertheless it seems reasonable to evaluate the applicability of thermography as a tool for determining temperature distributions on the surface of, e.g., light diffusers or biological tissue in the field of laser medicine. The assessment of tissue-heating in treatments like interstitial photodynamic therapy (iPDT) is of particular interest since additional tissue damage due to tissue heating is usually undesired and has thus to be avoided. Monte Carlo based simulations of the expected heat distribution in tissue are based on idealized setups. They usually omit certain characteristics of fibers, like inhomogeneities in a light diffuser or losses at components such as internal mirrors, that might potentially result in local hot spots and therefore in heating beyond an acceptable temperature. Experimental techniques based on thermocouples, or similar point-based temperature measurement devices, provide only a limited view of the temperature distribution inside or at the surface of the treated tissue. As a high resolution non-contact wide-field technique thermography although has some limitations. We present an evaluation of the usefulness of thermographic methods for recording the heat distribution on tissue and tissue phantom surfaces during laser treatment in an iPDT-like setup and compare the results with Monte Carlo based simulations.