Lasers in Medical Science

, Volume 12, Issue 3, pp 182–199

Implicit and explicit dosimetry in photodynamic therapy: a New paradigm


  • B. C. Wilson
    • Ontario Cancer Institute
    • Department of Medical BiophysicsUniversity of Toronto
    • Ontario Laser and Lightwave Research Centre
  • M. S. Patterson
    • Hamilton Regional Cancer Center and Departments of Radiology and PhysicsMcMaster University
  • L. Lilge
    • Department of Medical BiophysicsUniversity of Toronto
    • Ontario Laser and Lightwave Research Centre
Review Article

DOI: 10.1007/BF02765099

Cite this article as:
Wilson, B.C., Patterson, M.S. & Lilge, L. Laser Med Sci (1997) 12: 182. doi:10.1007/BF02765099


Dosimetry for photodynamic therapy (PDT) is becoming increasingly complex as more factors are identified which may influence the effectiveness of a given treatment. The simple prescription of a PDT treatment in terms of the administered photosensitizer dose, the incident light and the drug-light time interval does not account for patient-to-patient variability in either the photosensitizer uptake, tissue optical properties or tissue oxygenation, nor for the interdependence of the photosensitizer-light-tissue factors. This interdependence is examined and the implications for developing adequate dosimetry for PDT are considered. The traditional dosimetric approach, measuring each dose factor independently, and termed here ‘explicit dosimetry’, may be contrasted with the recent trend to use photosensitizer photobleaching as an index of the effective delivered dose, termed here ‘implicit dosimetry’. The advantages and limitations of each approach are discussed, and the need to understand the degree to which the photobleaching mechanism is linked, or ‘coupled’, to the photosensitizing mechanism is analysed. Finally, the influence of the tissue-response endpoints on the optimal dosimetry methods is considered.

Key words

Photodynamic therapyDosimetryPhotobleachingTissue response
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Copyright information

© W.B. Saunders Company Ltd 1997