Optimization of the Diameter of a Radial Irradiation Device for Photodynamic Therapy in the Esophagus

Photodynamic therapy (PDT) is a local therapeutic technique based on the photosensitization of lesions using a dye prior to light-induced tissue destruction. PDT of intraepithelial neoplasia in Barrett's esophagus, or of early squamous-cell carcinoma of the esophagus, requires light application devices that allow homogeneous and well-defined illumination of the tissue surface. Such devices must be large enough to induce complete unfolding of the esophagus in spite of esophageal motility and elasticity. The aim of this study was therefore to determine the optimal diameter of a cylindrical illumination device for PDT in this organ. The study included nine patients (aged 49-72 years) who underwent panendoscopy. Flexible transparent hollow tubes with diameters ranging from 13 to 19 mm were successively introduced into the esophagus, and the esophageal wall was viewed from the inside through the tube using a flexible small-diameter endoscope. The number of folds was counted. Observations of the upper, middle, and lower thirds of the esophagus were recorded. The radial location of the folds was also recorded, and defined as follows: anterior wall (up), posterior wall (down), side walls (right, left). No significant difference in the number of folds between the lower and middle parts of the esophagus was noticed. However, the upper third had significantly fewer folds (about 30 %) than the other two parts. For diameters above 17 mm, this difference was less dramatic. The number of such folds was shown to decrease with the increasing diameter of the device. It appears that 18 mm or more is the optimal diameter for a fixed-geometry cylindrical photodynamic therapy irradiating device for the patient category considered in this study. It was also observed that most folds were located on the side walls of the esophagus.