Lasers in Medical Science

, Volume 12, Issue 3, pp 182–199 | Cite as

Implicit and explicit dosimetry in photodynamic therapy: a New paradigm

  • B. C. Wilson
  • M. S. Patterson
  • L. Lilge
Review Article


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 therapy Dosimetry Photobleaching Tissue response 


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Copyright information

© W.B. Saunders Company Ltd 1997

Authors and Affiliations

  • B. C. Wilson
    • 1
    • 2
    • 3
  • M. S. Patterson
    • 4
  • L. Lilge
    • 2
    • 3
  1. 1.Ontario Cancer InstituteToronto, OntarioCanada
  2. 2.Department of Medical BiophysicsUniversity of TorontoToronto, OntarioCanada
  3. 3.Ontario Laser and Lightwave Research CentreToronto, OntarioCanada
  4. 4.Hamilton Regional Cancer Center and Departments of Radiology and PhysicsMcMaster UniversityHamilton,OntarioCanada

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