Singlet oxygen dosimetry modeling for photodynamic therapy.

Area of Science:

• Biomedical Engineering
• Photodynamic Therapy
• Cancer Research

Background:

• Photodynamic therapy (PDT) is a key treatment for localized diseases, including cancer.
• Singlet oxygen (¹O₂) is the primary cytotoxic agent in PDT, making its concentration a critical dosimetry quantity.
• Accurate measurement of ¹O₂ concentration is essential for determining PDT treatment efficacy.

Purpose of the Study:

• To develop and validate a photodynamic therapy (PDT) dosimetry model for calculating singlet oxygen (¹O₂) concentration.
• To determine key photo-physiological parameters influencing ¹O₂ generation.
• To establish reacted ¹O₂ concentration as an explicit dosimetry quantity for PDT.

Main Methods:

• A PDT dosimetry model was implemented using the finite-element method (FEM) in COMSOL.
• The model integrates light transport diffusion equations and macroscopic kinetic equations for ¹O₂ generation.
• Five photo-physiological parameters were explicitly determined, and ¹O₂ concentration profiles were calculated iteratively using mice experimental data.

Main Results:

• The developed FEM model successfully predicted singlet oxygen (¹O₂) generation and concentration.
• Apparent reacted ¹O₂ concentration was obtained as an explicit PDT dosimetry quantity.
• Photo-physiological parameters and reacted ¹O₂ concentrations were determined for Photofrin and BPD Verteporfin sensitizers.

Conclusions:

• The validated PDT dosimetry model provides an accurate method for quantifying singlet oxygen (¹O₂) concentration.
• This approach enables precise PDT dosimetry, enhancing treatment efficacy and predictability.
• The model's ability to determine photo-physiological parameters offers insights into sensitizer performance.