Pilot study on light dosimetry variables for photodynamic therapy of Barrett's esophagus with high-grade dysplasia

Photodynamic therapy (PDT) is used to treat Barrett's esophagus with high-grade dysplasia and mucosal carcinoma. Outcomes are variable with some patients having persistent disease, whereas others develop strictures. The aims of this study were (a) to compare porfimer sodium tissue uptake, light dose, and esophageal thickness with clinical outcomes and (b) to determine the selectivity of porfimer sodium uptake in diseased and normal epithelium.

Forty-eight hours after porfimer sodium infusion, patients underwent mucosal biopsy for quantification of the porfimer sodium. Laser light was delivered at 48 hours and again 24 or 48 hours later. Porfimer sodium was extracted from the biopsy samples and quantified using fluorescence spectroscopy. The enhanced photodynamic dose was determined as [porfimer sodium content * light dose/esophageal thickness]. PDT efficacy was determined 6 to 8 weeks later based on persistence or complete ablation of dysplasia or carcinoma.

Mean porfimer sodium content of 6.2 mg/kg (range, 2.6-11.2 mg/kg) and mean total light dose of 278 J/cm (range, 225-360 J/cm) resulted in a complete treatment. Mean porfimer sodium tissue content of 3.9 mg/kg (range, 2.1-8.1 mg/kg) and mean total light dose of 268 J/cm (range, 250-350 J/cm) resulted in an incomplete treatment. The total esophageal thickness (range, 1.7-6.0 mm) and enhanced photodynamic dose were correlated with treatment outcome.

Esophageal thickness is the strongest predictor of treatment outcome. The porfimer sodium content of Barrett's and normal tissue is not significantly different. "Photodynamic dose" for esophageal PDT should incorporate the esophageal thickness.