Optimizing light dosimetry in photodynamic therapy of the bronchi by fluorescence spectroscopy

Under identical conditions (drug and light dose, timing), the results of photodynamic therapy (PDT) of carcinomas of the bronchi with tetra(meta-hydroxyphenyl)chlorin (mTHPC) show large variations between patients. Before patients underwent PDT treatment, the mTHPC level was measured in the lesion, the normal surrounding tissue and the oral cavity, with an apparatus based on fluorescence spectroscopy. The fluctuations in degree of tissue reaction and tumour destruction between patients could be explained by individual variations in the mTHPC level in the mucosa of the bronchi. The patients who showed the highest mTHPC fluorescence signal also had the strongest response to PDT. In addition, a correlation between the mTHPC level in the oral cavity and bronchial mucosa was found. It is concluded that PDT can be improved by measuring the mTHPC level in the bronchi or the oral cavity before treatment by fluorescence spectroscopy, and then by adjusting the light dose to be applied to the observed mTHPC level.