PDT uses a light source such as a laser combined with a light-sensitive drug (photosensitising agent) to destroy cancer cells. The light-sensitive drug makes cells more responsive to light.
For this procedure, the patient gets injected with the light-sensitive drug. The drug is attracted to cancer cells more than normal cells. The drug does not do anything until it is exposed to a special kind of light. When the light is directed at the area of the cancer, the drug is activated and the cancer cells are destroyed.
There are different types of these drugs and each drug is activated by a different wavelength of light. The wavelength determines how far the light can travel in the body. So, the doctors use different light-sensitive drugs and different wavelengths of light to treat different areas of the body with PDT.
How does PDT work?
PDT is a two step cancer treatment. First the patient is given an injection of the light-sensitive drug. The drug will be absorbed by the body's tissues over the next couple of days. The drug gets absorbed by cells all over the body, but stays in cancer cells longer than it does in normal cells.
The second step begins approximately 40 to 50 hours after the light sensitive drug injection. Light from a laser will be aimed at at the cancer cells by the doctor. This takes approximately 5 to 40 minutes depending on the amount of cancer the doctor wants to treat. For many patients the entire procedure takes under one hour. The light will activate the drug present within those cells and destroy them.
Because the light sensitive drug is absorbed more by cancer cells and the laser is directed only to the area that needs treatment, most of the healthy tissue surrounding the treated area will not be affected.
In addition to directly killing cancer cells, PDT appears to shrink or destroy tumors in two other ways. The light sensitive drug can damage the blood supply to the tumor, preventing the cancer from growing. And PDT may trigger the immune system to attack the cancer cells.
How PDT is used
Photodynamic Therapy (PDT) may be done as an outpatient procedure. PDT may also be repeated and may be used with other therapies, such as surgery, radiation, or chemotherapy.
So far, in the United States, the U.S. Food and Drug Administration (FDA) has approved the light sensitive agent called Photofrin®, as a cancer treatment for certain patients with esophageal cancer or non-small cell lung cancer. The FDA has also approved Photofrin®, for the treatment of precancerous lesions in patients with Barrett's esophagus.
Doctors are currently studying ways to improve PDT and treat other cancers with light. Research studies are evaluating the use of PDT for cancers of the brain, skin, prostate, cervix, liver, and peritoneal cavity. Other studies are focusing on the development of light sensitive drugs that are more powerful, more precise, and able to infiltrate tissue and treat deep or large tumors. Researchers are also investigating ways to improve lasers and the delivery of the light.
What are the side effects of PDT?
Photofrin makes the skin and eyes sensitive to light for approximately 4-6 weeks after treatment. Patients are instructed to avoid direct sunlight and bright indoor light for at least 6 weeks. Patients should be given specific instructions from their PDT team on light precautions.
PDT can cause burns, swelling, pain, and scarring in healthy tissue nearby the cancerous areas being treated. This should be minimal though because light sensitive drugs accumulate in cancer cells and the activating light is focused on the tumor. Other temporary side effects of PDT are related to the area that is treated. These can include coughing, trouble swallowing, stomach pain, painful breathing, or shortness of breath.
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