Photodynamic therapy for esophageal lesions: Selectivity depends on wavelength, power, and light dose

Background. Photodynamic therapy with 5-aminolevulinic acid-induced photose nsitization could selectively eliminate esophageal epithelial lesions. This study aimed at optimizing laser parameters for 5-aminolevulinic acid photo dynamic therapy of the normal rat esophagus. Methods. Sixty rats received 200 mg/kg 5-aminolevulinic acid orally and wer e illuminated 3 hours later with either 633 or 532 nm light (n = 30 for eac h group) through an endoesophageal balloon catheter. Rats received either 8 .3 or 25 J/cm diffuser, applied with a 33, 100, or 300 mW/cm diffuser. Duri ng illumination, tissue fluorescence measurements and light dosimetry were done. Rats were sacrificed at 48 hours after photodynamic therapy. Results. During illumination, protoporphyrin IX fluorescence declined faste r when a higher power output was used. Fluence rate at the esophageal surfa ce was highest for 633-nm light. At 532 nm, light caused less damage to the epithelium and muscle than 633-nm light. Illumination with 33 mW resulted in selective epithelial ablation, whereas illumination with 300 mW caused m uscle damage with minor epithelial damage. Conclusions. The assumed selective epithelial damage of 5-aminolevulinic ac id photodynamic therapy in the esophagus largely depends on the combination of wavelength, power, and light dose applied. Most selective epithelial da mage was found when low-power 633-nm light was used. (C) 1999 by The Societ y of Thoracic Surgeons.