Light dosimetry for photodynamic therapy in the esophagus

Photodynamic therapy (PDT) is an efficient technique to treat superficial early cancers in the pharynx, esophagus, and tracheo-bronchial tree. However, the lack of selectivity of some of the clinically used photosensitizers can result in significant damage to the healthy tissue during the treatment. In the esophagus, this may lead to medical complications such as stenosis and fistula. Insufficient selectivity may be compensated to some extent by accurate light dosimetry. Here, we present an approach to safer and more efficient PDT by improved light dosimetry in the esophagus.

This includes the utilization of a suitable light distributor, the estimation of the radiant energy density in the tissue, and the knowledge of the esophagus morphology. The light distributor presently used in the clinic is described and several techniques to study light propagation in the esophageal wall have been investigated and are discussed. Thickness of different histological layers of the esophageal wall have been measured ex vivo and are presented.

Under these conditions and based on a simple model of the light distribution in the tissue, some basic and clinically useful notions of light dosimetry can be drawn. These notions, associated with measured value of tissue optical properties at the wavelengths of interest with the presently used photosensitizers, are discussed regarding the particular morphology of the esophageal wall. In particular, the importance of the illumination wavelength from the safety point of view is shown.

The proposed approach allows for improved safety and efficacy of PDT in the esophagus, particularly in the clinical tests of new photosensitizers.