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Photodynamic
therapy (PDT)
is a type of cancer treatment based on the premise that single-celled
organisms, if first treated with certain photosensitive drugs, will die when
exposed to light at a particular frequency. PDT destroys cancerous cells by
using this fixed frequency light to activate photosensitizing drugs which have
accumulated in body tissues.
In PDT, a photosensitizing drug is administered intravenously. Within a
specific time frame (usually a matter of days), the drug selectively
concentrates in diseased cells, while rapidly being eliminated from normal
cells. The treated cancer cells are then exposed to a laser light chosen for
its ability to activate the photosensitizing agent. This laser light is
delivered to the cancer site, (in the case of mesothelioma, the pleura),
through a fiberoptic device that allows the laser light to be manipulated by
the physician. As the agent in the treated cells absorbs the light, an active
form of oxygen destroys the surrounding cancer cells. The light exposure must
be carefully timed, so that it occurs when most of the photosensitizing drug
has left the healthy cells, but is still present in cancerous ones.
The major side effect of PDT is skin sensitivity. Patients undergoing this type
of therapy are usually advised to avoid direct and even indirect sunlight for
at least six weeks. Other side effects may include nausea, vomiting, a metallic
taste in the mouth, and eye sensitivity to light. These symptoms may sometimes
come as a result of the injection of the photosensitizing agent.
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