Fluorescence detection of small gastrointestinal tumours: principles, technique, first clinical experience

Photodynamic therapy (PDT) is a form of cancer treatment based on the selec tive accumulation of a photosensitizer in neoplastic tissue. The fluorescen t properties of a photosensitizer permit diagnostic localization of primary tumours and/or metastasis. occult lesions are hard to detect and can easil y be missed during routine laparoscopy. Fluorescence observation offers add itional optical information and the ability to detect these occult tumours. Clinically, we used 5-aminolevulinic acid for peritoneal staining and tumo ur demarcation via tumour-specific fluorescence induced by protoporphyrin I X. For laparoscopic observations, a "D-Light" system was used; the conventi onal white light source was equipped with an optical blocking filter that t ransmits at the excitation wavelength (380-450 nm) and blocks all other par ts of the spectrum. With the aid of a suitable observation filter, the rele vant fluorescence was detectable. With the help of this fluorescence we inc reased the capacity to detect occult tumours, that were missed with white-l ight observation (9/26). In the gastrointestinal tract, we used a krypton l aser at 405 nm for PP IX fluorescence induction. Although there were high s ensitivity rates for neoplasms (81% peritoneal carcinomas, 60% gastric canc er), no exact histopathological statement could be achieved at because of f alse-positive fluorescence, mainly caused by inflammation (6/32). Current c linical goals and the future perspectives of photodynamic diagnostic are di scussed.