Stability of the fluorescence measurement of Foscan (R) in the normal human oral cavity as an indicator of its content in early cancers of the esophagus and the bronchi

Photodynamic therapy (PDT) with Foscan(R) (mTHPC) is used to cure early can cers of the esophagus or the tracheobronchial tree. However, fixed PDT para meters (drug dose, light dose, etc.) do not permit an accurate prediction o f the tissue damage. Large interpatient fluctuations in tissue drug level, at the time of light application, suggest that the light dose must be adjus ted to the drug dose shortly before the PDT, This drug dose can be measured endoscopically by light-induced fluorescence spectroscopy, but this measur ement is inconvenient and somewhat difficult. A better test site, yielding comparable information, is needed, The oral cavity seems ideal. However, it first had to be established to what extent the estimation of the drug dose was dependent upon the location of the measurement and the pressure applie d to the probe. These measurements prove to be not only correlated to simil ar measurements in the esophagus or the bronchi but also more consistent an d less sensitive to the location and the applied pressure. The buccal mucos a is therefore recommended as a test site for measuring the Foscan(R) fluor escence signal at the time of PDT in the esophagus or the bronchi, This mea surement is accurate enough for use in light-dose adjustment.