Light delivery and light dosimetry for photodynamic therapy of bronchogenic carcinoma

Photodynamic tllel'apy (PDT) is a treatment modality for malignant (and benign) diseases that combines administration of a chemical compound (photosensitiser) and irradiation with (visible) light of the proper wavelength and fluence to induce tissue necrosis. The mechanisms by. which PDT induces cell death are not yet fully understood. The basic principle is that the iIIumination of the sensitiser causes excitation of the oxygen present in the tissue to the very reactive singlet state that induces damage to the tissue. The oxygen supply in the treated tissue is therefore of paramount importance for the final damage induced. Two types of damage are thought to be most important for the induced necrosis. Firstly, important (tumour)cell structures such as mitochondrial and cellular membranes are damaged with consequent direct cell death. Secondly, through damage of the endothelium of the blood vessels vascular stasis occurs which causes tissue damage as a secondary process.