In vivo spectroscopic evaluation of human tissue optical properties and hemodynamics during HPPH-mediated photodynamic therapy of pleural malignancies.

Abstract

Dosimetry for photodynamic therapy is dependent on multiple parameters. Critically, in vivo tissue optical properties and hemodynamics must be determined carefully to calculate the total delivered light dose. Spectroscopic analysis of diffuse reflectance measurements of tissues taken during a clinical trial of 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a-mediated photodynamic therapy for pleural malignancies. Diffuse reflectance measurements were taken immediately before and after photodynamic therapy. Measurements were analyzed with a nonlinearly constrained multiwavelength, multi-distance algorithm to extract tissue optical properties, tissue oxygen saturation, StO2, and total hemoglobin concentration (THC). A total of 25 patients were measured, 23 of which produced reliable fits for optical property extraction. For all tissue types, StO2 ranged through [24, 100]% and [22, 97]% for pre-photodynamic therapy (PDT) and post-PDT conditions, respectively. Mean THC ranged through [ 69,152 ] μM and [ 48,111 ] μM, for pre-PDT and post-PDT, respectively. Absorption coefficients, μa, ranged through [ 0.024 , 3.5 ] cm - 1 and [ 0.039 , 3 ] cm - 1 for pre-PDT and post-PDT conditions, respectively. Reduced scattering coefficients, μs', ranged through [ 1.4 , 73.4 ] cm - 1 and [ 1.2 , 64 ] cm - 1 for pre-PDT and post-PDT conditions, respectively. There were similar pre- and post-PDT tissue optical properties and hemodynamics. The high variability in each parameter for all tissue types emphasizes the importance of these measurements for accurate PDT dosimetry.