Refining photochemical dose–response modeling in single-fraction Photofrin-PDT using [ROS]X and MSOLD correlation

Photodynamic therapy (PDT) efficacy is governed by singlet oxygen generation, which depends on light delivery, photosensitizer concentration, and tissue oxygenation. Conventional fluence-based dosimetry does not explicitly account for these interacting factors and often exhibits variability in treatment response. In this study, we examine the relationship between modeled reacted singlet oxygen dose and long-term tumor control in a murine Photofrin-mediated PDT model under standardized illumination conditions. Tumors were treated using a 630nm continuous-wave laser at a fixed fluence rate of 150mW/cm², with total fluence varied by adjusting treatment time to produce four treatment groups (≈180–337J/cm²). Group-averaged reacted singlet oxygen dose ([ROS]ₓ) was estimated using the ROSED photochemical model incorporating measured photosensitizer concentration and tumor oxygenation. Local control rate (LCR) was assessed using Kaplan–Meier analysis. In a subset of animals, multispectral singlet oxygen luminescence detection (MSOLD) was performed to directly measure singlet oxygen emission during PDT. A monotonic increase in LCR was observed with increasing group-averaged [ROS]ₓ, while fluence alone showed greater variability. MSOLD measurements confirmed singlet oxygen generation across all treatment groups. Although instantaneous MSOLD signals exhibited substantial temporal variability, cumulative MSOLD signals increased approximately linearly with illumination time and showed group-dependent differences consistent with modeled photochemical dose. These results support the use of photochemical dose metrics incorporating physiological parameters as a more biologically relevant descriptor of PDT response than fluence alone and establish a refined single-fraction baseline for future PDT dosimetry studies.