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Photodynamic therapy (PDT) is a special form of phototherapy, a term which includes
all treatments which use light to induce reactions in the body which are of benefit
to patients.
PDT is a developing technique which can potentially destroy unwanted tissue,
whilst sparing normal tissue. First a drug called a photosensitiser
is administered to the patient, usually by injection. The photosensitiser alone is
harmless and has no effect on either healthy or abnormal tissue. However, when light (often from
a laser) is directed onto tissue containing the drug, the drug becomes activated and the tissue is
rapidly destroyed, but only precisely where the light has been directed. Thus, by careful
application of the light beam, the technique can be targeted selectively to the abnormal tissue.
Some of the drugs being developed also have the desirable property of concentrating in tumours
(and certain other kinds of proliferating tissue) relative to the surrounding healthy tissue, which
also helps in targeting. There is only one potentially adverse effect - some drugs can
result in skin photosensitivity, which means that patients must stay out of bright light for some
time following the administration of the drug.
PDT, using the drug Photofrin®, has now been approved as a therapy for, as yet, a limited number of
applications in various parts of the world including the UK and it is now clear that there are some
indications where PDT is at least as good as and possibly better than alternative treatments.
However it has to be emphasised that PDT is still largely an experimental therapy and is currently
only applicable to a very small range of patients. More research is needed to further develop and
assess PDT with different drugs in different clinical situations. Nevertheless there is growing
confidence that PDT will soon become an added weapon in the fight against cancer and other diseases.
The way that PDT works in patients in shown below:
A patient comes to the clinic with a tumour.
The photosensitiser is given by injection. |
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After time the photosensitiser concentrates in the tumour. |
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| The photosensitiser is activated by light. |
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The tumour is selectively destroyed. |
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