Oxygen saturation and perfusion changes during dermatological methylaminolaevulinate photodynamic therapy

Authors

  • J. Tyrrell,

    1. Clinical Photobiology, European Centre for Environment and Human Health, Peninsula Medical School, University of Exeter, Royal Cornwall Hospital, Truro TR1 3HD, U.K.
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  • C. Thorn,

    1. Diabetes and Vascular Medicine, Peninsula NIHR Clinical Research Facility and Peninsula Medical School, University of Exeter, Royal Devon and Exeter Hospital, Exeter EX2 5AX, U.K.
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  • A. Shore,

    1. Diabetes and Vascular Medicine, Peninsula NIHR Clinical Research Facility and Peninsula Medical School, University of Exeter, Royal Devon and Exeter Hospital, Exeter EX2 5AX, U.K.
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  • S. Campbell,

    1. Clinical Photobiology, European Centre for Environment and Human Health, Peninsula Medical School, University of Exeter, Royal Cornwall Hospital, Truro TR1 3HD, U.K.
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  • A. Curnow

    1. Clinical Photobiology, European Centre for Environment and Human Health, Peninsula Medical School, University of Exeter, Royal Cornwall Hospital, Truro TR1 3HD, U.K.
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  • Funding sources
    This work was kindly funded by the Duchy Health Charity.

  • Conflicts of interest
    None declared.

Alison Curnow.
E-mail: alison.curnow@pms.ac.uk

Summary

Background  Methylaminolaevulinate (MAL)-photodynamic therapy (PDT) is a successful topical treatment for a number of (pre)cancerous dermatological conditions. In combination, light of the appropriate wavelength, the photosensitizer protoporphyrin IX (PpIX) and tissue oxygen result in the production of singlet oxygen and reactive oxygen species inducing cell death.

Objectives  This study investigates real-time changes in localized tissue blood oxygen saturation and perfusion in conjunction with PpIX fluorescence monitoring for the first time during dermatological MAL-PDT.

Methods  Oxygen saturation, perfusion and PpIX fluorescence were monitored noninvasively utilizing optical reflectance spectroscopy, laser Doppler perfusion imaging and a fluorescence imaging system, respectively. Patients attending for standard dermatological MAL-PDT were recruited to this ethically approved study and monitored prior to, during and after light irradiation.

Results  Significant reductions in mean blood oxygen saturation (< 0·005) and PpIX fluorescence (< 0·001) were observed within the first minute of irradiation (4·75 J cm−2) while, in contrast, perfusion was observed to increase significantly (< 0·01) during treatment. The changes in oxygen saturation and PpIX fluorescence were positively correlated during the initial phase of treatment (r2 = 0·766).

Conclusions  Rapid reductions in the localized blood oxygen saturation have been observed for the first time to occur clinically within the initial minutes of light irradiation and positively correlate with the concurrent PpIX photobleaching. Furthermore, perfusion increases, suggesting that the microvasculature compensates for the PDT-induced oxygen depletion.

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