Light dosimetry calculations for esophageal photodynamic therapy using porfimer sodium

Background: Photodynamic therapy using porfimer sodium (Ps-PDT) is approved for use in patients with Barrett's high-grade dysplasia and esophageal carcinoma. Ps-PDT light dosimetry, however, is critically important to treatment outcomes since insufficient ablation results in residual dysplasia and carcinoma while excessive treatment results in stricture formation. Aim: The aim of this study was to model esophageal PDT with optical absorption and scattering coefficients derived from an ex-vivo porcine multilayer esophagus model. Methods: Optical coefficients were derived for the mucosal and muscle layers of normal pig esophagus. The mucosal layer (mucosa, muscularis mucosa and submucosa) was separated from the muscle layer. Diffuse reflectance and transmittance were measured with an integrating sphere spectrophotometer. Absorption and reduced scattering coefficients were determined with the inverse adding doubling method. Wavelength Tissue μ eff μ a μ s' (nm) type mm ^-1 mm ^-1 mm ^-1 630 mucosa 0.522 0.068 1.27 630 Muscle layer 0.521 0.109 0.722 630 Whole esophagus 0.482 0.061 1.21 Multilayer Monte Carlo simulation and single-layer mathematical dosimetry equations were employed to model esophageal PDT with the derived coefficients. Porfimer sodium addition was modeled with an increase in both absorption and scattering. Depth of injury, assumed to require a threshold light dose, was estimated for various light doses commonly used in clinical practice. Depth of injury was then compared to clinical outcomes reported in the literature for various light doses.