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Photodynamic Therapy

Photodynamic therapy is a method of treating cancer. It is administered using a special drug and a specific type of light. When photosensitizers are exposed to a specific wavelength of light, they produce a form of oxygen that kills nearby cells. This form of therapy is usually used to treat tumors on or just under the skin or on the lining of internal organs or cavities rather than cases where the cancer has spread.

What Is Photodynamic Therapy?

Photodynamic therapy (PDT) is a type of treatment that uses a drug, called a photosensitizer or photosensitizing agent, and a particular type of light. When photosensitizers are exposed to a specific wavelength of light, they produce a form of oxygen that kills nearby cells.
Each photosensitizer is activated by light of a specific wavelength. This wavelength determines how far the light can travel into the body. Thus, doctors use specific photosensitizers and wavelengths of light to treat different areas of the body with photodynamic therapy.

How Does It Work?

In the first step of photodynamic therapy for cancer treatment, a photosensitizing agent is injected into the bloodstream. The agent is absorbed by cells all over the body, but stays in cancer cells longer than it does in normal cells. Approximately 24 to 72 hours after injection, when most of the agent has left normal cells but remains in cancer cells, the tumor is exposed to light. The photosensitizer in the tumor absorbs the light and produces an active form of oxygen that destroys nearby cancer cells.
In addition to directly killing cancer cells, photodynamic therapy 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. In addition, this form of therapy may activate the immune system to attack the tumor cells.
The light used for photodynamic therapy can come from a laser or other sources of light. Laser light can be directed through fiber-optic cables (thin fibers that transmit light) to deliver light to areas inside the body. For example, a fiber-optic cable can be inserted through an endoscope (a thin, lighted tube used to look at tissues inside the body) into the lungs or esophagus to treat cancer in these organs. Other light sources include light-emitting diodes (LEDs), which may be used for surface tumors, such as skin cancer.
Photodynamic therapy is usually performed as an outpatient procedure. It may also be repeated and used with other therapies, such as surgery, radiation, or chemotherapy.
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