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Photodynamic Therapy

Biomedical Spectroscopy

  1. Beate Röder

Published Online: 15 SEP 2006

DOI: 10.1002/9780470027318.a0115

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Röder, B. 2006. Photodynamic Therapy. Encyclopedia of Analytical Chemistry. .

Author Information

  1. Humboldt-University Berlin, Institute of Physics, Berlin, Germany

Publication History

  1. Published Online: 15 SEP 2006


Photodynamic therapy (PDT) is an effective treatment of different types of cancer, virus infections, skin diseases and others using photosensitizers (PSs) which are nontoxic in the dark but become phototoxic following activation by low energy light. The PS is applied topically or systemically and should be selectively accumulated in the target tissue. The molecular mechanism of the therapy is the photodynamic effect: following light absorption energy is transferred from the PS to molecular oxygen generating singlet molecular oxygen (1O2) which causes direct or indirect photodamage of the target tissue.

In clinical therapy with first generation PSs like Photofrin® typically fluences of around 100 J cm−2 of red light are used. The light doses vary in dependence on the treated disease. Using PSs of second generation with very strong absorption in the red region like the very efficient m-tetrahydroxyphenylchlorin (m-THPC), smaller fluences, typically around 10 J cm−2, are required. According to the different optical properties and the efficiency of selective accumulation of PS in the target tissue, the drug doses vary from 1–5 mg (first generation PS) to 0.1 mg (second generation PS) per kilogram body weight.

PDT is a very efficient method for the treatment of minor diseases, blood cancer, inoperable diseases like some types of bladder, brain or lung cancer, and breast carcinoma metastases. The side effects are less than in the case of chemo- or radiotherapy. The most common side effect is skin photosensitization. The strength of this effect depends on the PS used and also on the patients' skin type. Most of the new second generation PSs cause no or only weak skin phototoxicity. The therapeutic radius is limited by the penetration depth of the used light (in the order of some millimeters to centimeters). The method will not be very successful for the treatment of large solid tumors.