A feasibility study of singlet oxygen explicit dosmietry (SOED) of PDT by intercomparison with a singlet oxygen luminescence dosimetry (SOLD) system

Abstract

An explicit dosimetry model has been developed to calculate the apparent reacted ¹<i>O</i>₂ concentration ([¹<i>O</i>₂]_rx) in an <i>in-vivo</i> model. In the model, a macroscopic quantity, <i>g</i>, is introduced to account for oxygen perfusion to the medium during PDT. In this study, the SOED model is extended for PDT treatment in phantom conditions where vasculature is not present; the oxygen perfusion is achieved through the air-phantom interface instead. The solution of the SOED model is obtained by solving the coupled photochemical rate equations incorporating oxygen perfusion through the air-liquid interface. Experiments were performed for two photosensitizers (PS), Rose Bengal (RB) and Photofrin (PH), in solution, using SOED and SOLD measurements to determine both the instantaneous [¹O₂] as well as cumulative [¹O₂]_rx concentrations, where [¹O₂] <i>_rx</i> = (1/<i>τ</i>_Δ) · ∫[¹O₂]<i>dt</i>. The PS concentrations varied between 10 and 100 mM for RB and ~200 mM for Photofrin. The resulting magnitudes of [¹O₂] were compared between SOED and SOLD.