Photodynamic therapy and laser-based diagnostic studies of malignant tumours

Sammanfattning: Two non-thermal regimens of light interaction with biological tissue, that are in a natural way connected, are discussed in the present thesis. These are photodynamic therapy (PDT) for the treatment of malignant tumours and laser-induced fluorescence (LIF) for tissue characterization. In PDT, a photochemical reaction is induced by non-ionizing electromagnetic irradiation in tissue where photosensitizing agents and oxygen are present. Instead of using pre-formed photosensitizers for intravenous administration, a new way of sensitization was exploited. A porphyrin precursor, (delta)-aminolevulinic acid (ALA) was utilized for the induction of protoporphyrin IX (PpIX). Photodynamic therapy was used in the treatment of non-melanoma malignant skin tumours, mainly basal cell carcinomas (BCCs). A randomized, clinical trial was conducted in the treatment of BCCs, where PDT was compared to cryosurgery. Laser-induced fluorescence (LIF) can be applied for non-invasive, real time spectroscopic tissue characterization. Laser light is used for fluorescence excitation. The fluorescence signal in pre-malignant and malignant tissue exhibits some characteristics that deviate from those of normal tissue. In addition, the contrast can be increased by employing fluorescent tumour markers. Laser-induced fluorescence measurements were performed in malignancies of the skin and benign, pre-malignant and malignant lesions in the head-and-neck region. Again, ALA-induced PpIX was used. The build-up and the photodegradation of PpIX were also studied. Another non-invasive, real time method for tissue diagnostics is laser-Doppler imaging (LDI), for detection of the blood perfusion in superficial tissue. In the present work, the modality was used in connection with ALA-PDT of non-melanoma malignant skin tumours, for identifying lesions, characterize the vascular effects induced by the PDT and follow the healing process after treatment.