Laser light application and light monitoring for photodynamic therapy in hollow organs

Photodynamic therapy (PDT) of tumours in hollow organs requires light application devices which enable homogeneous illumination of the tissue surface in hollow organs. This paper presents two laser light application systems generating a homogeneous light distribution and one monitoring unit which detects variations in the applied laser light intensity during treatment. A cylindrical light diffuser has been developed for PDT of cylindrical organs (e.g. bronchus, oesophagus). This system guarantees a defined homogeneity of the laser light intensity. An exact positioning to a defined treatment area is possible. Adjacent tissue is prevented from laser light irradiation. A special lens system has been developed for the irradiation of flat surfaces (e.g. skin, carina, organ wall of the large bowel and the stomach). The illumination area is defined by the distance to the tissue and the large aperture. The size of the system allows for it to pass through the biopsy channel of conventional endoscopes. A monitoring device recently developed helps to detects of the fibre, changes in the medium around the fibre tip, and variations of the laser output power during laser treatment. All devices serve for evaluating an accurate light dosimetry in clinical PDT.