Although photodynamic therapy (PDT) is an established modality for cancer treatment, current dosimetric quantities, such as light fluence and PDT dose, do not account for the differences in PDT oxygen consumption for different fluence rates (). A macroscopic model was adopted to evaluate using calculated reacted singlet oxygen concentration () to predict Photofrin-PDT outcome in mice bearing radiation-induced fibrosarcoma tumors, as singlet oxygen is the primary cytotoxic species responsible for cell death in type II PDT. Using a combination of fluences (50, 135, 200, and ) and (50, 75, and ), tumor regrowth rate, , was determined for each condition. A tumor cure index, , was calculated based on the between PDT-treated groups and that of the control, . The measured Photofrin concentration and light dose for each mouse were used to calculate PDT dose and , while mean optical properties (, ) were used to calculate for all mice. CI was correlated to the fluence, PDT dose, and with , 0.79, and 0.93, respectively. These results suggest that serves as a better dosimetric quantity for predicting PDT outcome.