Photodynamic therapy (PDT) is a special light treatment that affects cells that are directly exposed. Photodynamic therapy has been approved by the FDA to treat certain dermatology and oncology conditions and has been also used experimentally to treat other diseases.
PDT involves a three-step process. First a photosensitizing drug is applied to the skin or given intravenously.
Next, time is allowed to pass so the drug can incubate, which helps allow the cells to become more receptive to the light. Finally, the cells are exposed to a laser light source, selected specifically for the type of condition the person has. This exposure activates the release of oxygen, which can destroy nearby cells.
When used as a cancer treatment, PDT not only kills cancer cells it “appears to shrink or destroy tumors in two other ways. The photosensitizer can damage blood vessels in the tumor, thereby preventing the cancer from receiving necessary nutrients. PDT also activates the immune system to attack the tumor cells.”(3)
In dermatology, PDT is used to treat actinic keratosis (AK), which is a pre-cancerous skin condition caused by sun damage and mycosis fungoides, a skin lymphoma.
The photosensitizing drugs used are Levulan or ALA, which is aminolevulinic acid, or MAL which is methyl aminolevulinate, which are applied directly to the skin areas to be treated. Blue laser light is the light source used to activate ALA and red laser light can be used for MAL treatments.
Off-label skin treatments using PDT “include the treatment of BCC (basal cell carcinoma), photoaging, acne vulgaris, and Bowen disease”, according to Medscape.
Using PDT for treatment of internal cancer can be more challenging. To reach some parts of the body, fiber optics must be used to expose cells to the laser light. For instance treatment of Barrett’s esophagus, which is a condition that may lead to esophageal cancer and endobronchial cancer, a type of non-small cell lung cancer, must both be treated using fiber optics passed through an endoscope to reach the cancer cells.
Porfimer sodium (Photofrin) is the photosensitizer used and is given intravenously. Two or three days after receiving the drug, red laser light is used to treat these types of cancers.
It is hoped that with further research that other cancers of the brain, prostate, cervix and organs in the abdominal cavity may be receptive to PDT.
PDT use has both pros and cons. The pros are these. It is less invasive than surgery, can be specifically targeted to a treatment area and repeated as necessarily with no long-term side effect if used properly. It is an alternative for those who can’t have other types of treatment, such as surgery or radiation therapy.
The limitation of its use is that it can only treat areas that light can reach at a 1/3 of an inch depth, so it is predominately used on skin or the lining of an organ.
Other side effects may include redness, swelling, burning, stinging and, for internal treatments, swelling could cause pain or trouble swallowing or breathing.
Afterwards, the person can remain sensitive to light for a long time afterwards so special precautions must be taken. Sensitivity to light can last 30 days with ALA or MAL and up to three months with Photofrin. People with certain blood diseases or who have allergies to porphyrins cannot receive PDT.
1. Photodynamic Therapy (PDT or Blue Light Therapy). MedicineNet.com.
2. Photodynamic Therapy for the Dermatologist. Medscape Reference.
Author: Jaggi Rao, MD, FRCPC.
3. Photodynamic Therapy for Cancer
4. Photodynamic Therapy. American Cancer Society. http://www.cancer.org/Treatment/TreatmentsandSideEffects/TreatmentTypes/...
Michele is an R.N. freelance writer with a special interest in woman’s healthcare and quality of care issues. Other articles by Michele are at www.helium.com/users/487540/show_articles
Edited by Jody Smith
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