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Photodynamic actinometry using microspheres: concept, development and responsivity.

Stuart K Bisland1, James W Austin, Daniel P Hubert

  • 1Princess Margaret Hospital, Ontario Cancer Institute, Toronto, Canada. sbisland@uhnres.uotoronto.ca

Photochemistry and Photobiology
|May 13, 2004
PubMed
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This study introduces novel fluorescent microspheres for precise photodynamic therapy (PDT) dosimetry. These microspheres accurately measure light dose and reactive oxygen species (ROS) generation in situ, crucial for advancing PDT treatments.

Area of Science:

  • Biomedical Engineering
  • Photochemistry
  • Materials Science

Background:

  • Photodynamic therapy (PDT) efficacy depends on precise dosimetry of light and reactive oxygen species (ROS) generation.
  • Current methods lack high-resolution, localized, in situ measurements critical for in vivo PDT development.
  • Accurate dosimetry is essential for optimizing PDT protocols and ensuring treatment effectiveness.

Purpose of the Study:

  • To develop a novel, fluorescent-based actinometer microsphere system for spatially resolved dosimetry in PDT.
  • To enable in situ measurement of total fluence and ROS production with high resolution.
  • To provide a tool for investigational PDT development and clinical dosimetry applications.

Main Methods:

  • Alginate-poly-L-lysine-alginate microspheres (80-200 microm) were fabricated using ionotropic gelation.

Related Experiment Videos

  • Microspheres incorporated two dyes: ADS680WS (inside) and Rhodophyta-phycoerythrin (RPE) (outside).
  • RPE's responsivity to ROS was tested using chemical (potassium perchromate) and photochemical induction; singlet oxygen confirmed via phosphorescence.

    • Main Results:

    • RPE fluorescence decrease correlated with increased perchromate concentration or PDT fluence, confirming ROS detection.
    • Photodegradation of RPE was independent of pH (6.5-8) and inhibitable by sodium azide; RPE showed no photobleaching alone.
    • ADS fluorescence decrease correlated directly with radiant exposure (600-750 nm), independent of irradiance.

    Conclusions:

    • Actinometer microspheres offer a high spatial resolution method for measuring delivered PDT dose in model systems.
    • This system can provide crucial dosimetric information for investigational PDT and clinical extracorporeal PDT applications.
    • The microsphere system enables accurate in situ quantification of fluence and ROS generation for PDT optimization.