Photodynamic Therapy (PDT)

Photodynamic therapy (PDT) is a treatment that uses light to damage cancerous or abnormal tissues. PDT requires a light source, such as a laser, combined with a drug that makes the tissues light-sensitive, which is known as a "photosensitizer." When the light and photosensitizer are combined, oxygen-free radicals that are able to destroy cancer cells are released. Photosensitizers are taken up in greater amounts by cancer cells than normal cells.

A photosensitizing drug is given to the patient by mouth, by an intravenous (IV) line, or topically (specifically to treat skin lesions) a few hours to days prior to the light exposure. The drug is not activated until it is exposed to a particular wavelength of light. When the light is directed at the area of the cancer, the photosensitizer is activated and the cancer cells are destroyed. This wavelength determines how far the light can travel into the body. PDT is generally not used to treat large tumors, because the light cannot reach the necessary depth to treat those tumors. Different photosensitizers are activated by different wavelengths of light. Depending on the area of the body to be treated, there are different photosensitizing drugs and different wavelengths of light that can be used.

What does PDT treat?

PDT is used to treat: 

• Obstruction caused by esophageal cancer or non-small-cell lung cancer (NSCLC). 
• Micro invasive endobronchial NSCLC when surgery or radiotherapy can not be used. 
• Barrett's Esophagus and high-grade dysplasia. 
• Actinic keratosis. 
• Age-related macular degeneration.

How does PDT work?

PDT is a multistep treatment process. First, the photosensitizer is administered to the patient. The drug takes a certain amount of time to be absorbed by the body. Exactly how much time is needed depends on the type of photosensitizer that is used, but typically takes a few days. The drug gets absorbed by cells all over the body but it stays in cancer cells longer than normal cells. Second, the provider directs a laser light source at the cancer cells. The amount of time that the laser is used will vary from patient to patient, according to the amount of disease present. In the presence of light from the laser, the photosensitizer will act on and damage the cancer cells. Since the photosensitizing drug is retained longer in the cancer cells, the cancer cells sustain more damage than the healthy cells that have already cleared the drug.

In PDT, cell death occurs in multiple ways. There can be direct damage to cells via interaction between oxygen and the cancer cells. There are also indirect effects, including damage to blood vessels that supply the tumor, both during the treatment and after the treatment is over. Damage to the tumor blood supply during or after PDT will deprive tumor cells of oxygen/nutrients, thereby enhancing responses. Finally, PDT also stimulates your immune system to attack the cancer cells.

PDT is often done as an outpatient procedure, depending on the site that is to be treated. PDT may also be repeated and may be done with other treatments, such as surgery, radiation, or chemotherapy.

What are the side effects of PDT?

Photosensitizers make the body sensitive to light. Your provider will tell you how long you should avoid light exposure. You will be given light precautions, such as avoiding direct sunlight and bright indoor light for a period of time. If light precautions are not followed, you could sustain burns, swelling, and pain. Other side effects of PDT are related to the area that is treated and can include coughing, trouble swallowing, stomach pain, painful breathing, swelling, and/or shortness of breath.