In vivo outcome study of BPD-mediated PDT using a macroscopic singlet oxygen model

Macroscopic modeling of the apparent reacted singlet oxygen concentration ([¹O₂]_rx) for use with photodynamic therapy (PDT) has been developed and studied for benzoporphryin derivative monoacid ring A (BPD), a common photosensitizer. The four photophysical parameters (ξ, σ, β, δ) and threshold singlet oxygen dose ([¹O₂]_rx,sh) have been investigated and determined using the RIF model of murine fibrosarcomas and interstitial treatment delivery. These parameters are examined and verified further by monitoring tumor growth post-PDT. BPD was administered at 1 mg/kg, and mice were treated 3 hours later with fluence rates ranging between 75 - 150 mW/cm² and total fluences of 100 - 350 J/cm². Treatment was delivered superficially using a collimated beam. Changes in tumor volume were tracked following treatment. The tumor growth rate was fitted for each treatment condition group and compared using dose metrics including total light dose, PDT dose, and reacted singlet oxygen. Initial data showing the correlation between outcomes and various dose metrics indicate that reacted singlet oxygen serves as a good dosimetric quantity for predicting PDT outcome.