Photodynamic therapy (PDT) is a medical treatment that uses a drug that becomes activated by light exposure (a photosensitizing drug) and a light source to activate the applied drug. The result is an activated oxygen molecule that can destroy nearby cells for example precancerous cells and certain types of cancer cells.
It is currently used in a number of medical fields including oncology (cancer), dermatology (skin), and cosmetic surgery and it can easily be performed in a physician's office or outpatient setting. Most skin PDT is performed only by specially trained dermatologists and their medical staff.
Other physicians, including oncologists, family physicians, internal medicine doctors, plastic surgeons, or ear, nose, and throat (ENT) surgeons and their medical staff who are trained, may also perform photodynamic therapy.
PDT has three steps:
- First, the photosensitizer liquid or cream is applied topically to the whole area being treated (such as the entire face, scalp, back of the hands, scalp, chest, back, etc.).
- The medication is allowed to air dry for a few minutes, and then the patient must wait 30-60 minutes for the incubation time, but some areas such as chest, back, and particularly forearms and legs require longer incubation times of two to 18 hours for better results.
- After the proper incubation time, in the light-source room medication is being activated with a specific wavelength light source. The patient may feel warmth, tingling, heat, or burning but a fan can be used to help cool off during the treatment. After treatment area is washed off and sunscreen applied. Instructions are given on how to care for the skin at home.
FDA-approved photosensitizers include Photofrin (porfimer sodium) which is used intravenously for internal cancers, and Levulan (5-aminolevulinic acid or ALA), and Metvix (methyl aminolevulinate [MAOP]) are applied topically for skin therapy. More drugs may become available in the near future.
PDT light sources include laser, intense pulsed light, light-emitting diodes (LEDs), blue light, red light, and many other visible lights (including natural sunlight). Photosensitizer drugs may become activated by one or several types of light and the optimal light depends on the ideal wavelength for the particular drug used and the target tissue.
The light source needs to be directly applied to the target tissue for a specific amount of time so for surface skin treatments (face, scalp, arms, etc.), the light is easily directly applied to the area of the skin where the photosensitizer drug has been applied, but for internal cancers, delivering the light to the desired area is more challenging.
The light may be delivered into the body cavity or area being treated through small fiber-optic cables –for example, the endoscopes (a thin, lighted, elongated tube that is inserted into a body space) are used to deliver the light into the lungs, stomach, or bladder.
PDT causes only a temporary sensitivity to light, including natural sunlight and some indoor lights and this resolves with time, depending on both the photosensitizer drug and dosage used but after PDT light avoidance is generally required.
Proper protection, including long sleeves and sunglasses, may be required after porfimer given intravenously for about six weeks after treatment. Topically applied aminolevulinic acid or methyl aminolevulinate may cause skin sensitivity only on the treatment areas for approximately 24-72 hours and these do not usually cause sensitivity on other body parts other than where the drug was directly applied.
Depending on the area being treated and the recommended incubation time, different numbers of treatment sessions spaced four to six weeks apart may be required to achieve the desired improvement and reduction in lesions. On average, a series of two to three treatments are performed.
