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What is photodynamic therapy (PDT)?
Photodynamic therapy(PDT) is a medical treatment that uses a photosensitizing drug ( a drug that becomes activated by light exposure) and a light source to activate the applied drug. The result is an activated oxygen molecule that can destroy nearby cells. Very thin superficial skin cancers called actinic keratoses and certain other types of cancer cells can be eliminated this way. The procedure is easily performed in a physician’s office or outpatient setting.
PDT essentially has three steps. first, a light-sensitizing liquid, cream, or intravenous drug(photosensitizer) is applied or administered. Second, there is an incubation period of minutes to days. finally, the target tissue is then exposed to a specific wavelength of light that then activates the photosensitizing medication.
How does photodynamic therapy work?
PDT works by direct injury to the target cells and tissues. This involves an antivated oxygen molecule that can injure or destroy nearby cells. Because the normal skin barrier is not present at the sites of the actinic keratoses, it is preferentially absorbed there and activated by light. The, the activated oxygen destroys the adjacent abnormal tissue. Once the areas have healed following PDT, the areas are reexamined to see if additional treatments or biopsies are needed.
With traditional cryosurgery (freezing with liquid nitrogen), only the visible actinic keratoses can be treated. Since many actinic keratoses are ofter not evident, this PDT allows for treatment of an entire area of sun damage simultaneously, but retreatments may be necessary.
What phtosensitizer drugs are available?
FDA-approved photosensitizers include Photofrin (porfimer sodium), Levulan (5-aminolevulinic acid or ALA), and Metvix (methyl aminolevulinate [MAOP]). More drugs may become available in the near future. Photofrin is used intravenously for internal cancers while Levulan and Metvix are applied topically for skin therapy.