On-line fluorescence of human tissues after oral administration of 5-aminolevulinic acid.

It is important to have a frame of reference for the timing of photodynamic therapy (PDT) using 5-aminolevulinic acid (ALA) so that PDT can occur when the tissue levels of protoporphyrin IX (PP) are at a maximum. This study describes a non-invasive fluorescence technique for detecting tissue PP levels after systemic ALA administration in patients with gastrointestinal cancer. The data suggest that the intensity of tumor surface fluorescence correlates with the tumor PP concentration. Spectrophotofluorometric measurements of skin and buccal mucosa also offer an easily acquired and rapid means for determining changes in plasma concentrations of PP. A number of potential variables, including blood flow, affect the intensity of fluorescence. We report that fluorescence measurements in situ are best adapted to the measurement of changes in the porphyrin levels in tissues rather than the absolute concentrations.

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