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Photodynamic Therapy (PDT)

Photodynamic therapy (PDT) is a 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 PDT.

When should photodynamic therapy be used?

PDT is usually used to treat tumors on or just beneath the skin, or on the lining of internal organs or cavities. Areas of treatment include pre-skin-cancers, esophageal cancer, and non-small cell lung cancer.

The light needed to activate most photosensitizers cannot pass through more than about one-third of an inch of tissue (1 centimeter). For this reason, PDT is usually used to treat tumors on or just under the skin or on the lining of internal organs or cavities. PDT was less effective in treating large tumors, because the light cannot pass far into these tumors. Developments have been made with light sources that can be implanted and custom shaped to any given tumor, so deep seated tumors that could never be treated now can be treated.

According to the National Cancer Institute, clinical trials are being conducted to evaluate the use of PDT for cancers of the brain, skin, prostate, cervix and peritoneal cavity. Also under development are more powerful photosensitizers, ways to more specifically target cancer cells and improve the delivery of the activating light.

PDT is also used in dermatology for fractional laser skin resurfacing, for conditions such as acne, actinic keratosis, and photo aging. A photosensitizer, such as 5-Aminolevulinic acid (ALA) or Methylaminolevulinate (MAL) is used with a fractional laser.

What devices are used to treat this condition?

Almost any laser with the appropriate output wavelength can be used for PDT.

Description of treatment

In the first step of PDT 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.

The light used for PDT can come from a laser or other sources. 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.

PDT is usually performed as an outpatient procedure. PDT may also be repeated and may be used with other therapies, such as surgery, radiation therapy, or chemotherapy.

Success rates/potential complications

Photosensitizers tend to build up in tumors and the activating light is focused on the tumor. As a result, damage to healthy tissue is minimal. However, PDT can cause burns, swelling, pain, and scarring in nearby healthy tissue. Other side effects of PDT are related to the area that is treated. They can include coughing, trouble swallowing, stomach pain, painful breathing, or shortness of breath; these side effects are usually temporary.

What outcome should patients expect?

In addition to directly killing cancer cells, PDT 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 may activate the immune system to attack the tumor cells.

Updated March 3, 2016


PDT
Merrill A. Biel, MD, PhD talks about the different areas that photodynamic therapy treats.

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The American Society for Laser Medicine and Surgery is the world’s largest scientific organization dedicated to promoting research, education and high standards of clinical care in the field of medical laser applications. It provides a forum for the exchange of scientific information and participation in communicating the latest developments in laser medicine and surgery to clinicians, research investigators, government and regulatory agencies, and the public.

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