Photodynamic Therapy
(PDT or Blue Light Therapy)
Medical Author: Nili N. Alai, MD, FAAD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR
What is photodynamic therapy?
Photodynamic therapy (PDT) is a medical treatment that uses a photosensitizing drug (a drug that becomes activated by light exposure) and a light source to activate the applied drug. The result is an activated oxygen molecule that can destroy nearby cells.
Precancerous cells and certain types of cancer cells can be treated this way. The
procedure is easily performed in a physician's office or outpatient setting.
PDT essentially has three steps. First, a light-sensitizing liquid, cream, or
intravenous drug (photosensitizer) is applied or administered. Second, there is
an incubation period of minutes to days. Finally, the target tissue is then
exposed to a specific wavelength of light that then activates the
photosensitizing medication.
Steps:
- application of photosensitizer drug
- incubation period
- light activation
Although first used in the early 1900s, PDT in the modern sense is a fairly
new, evolving science. Current PDT involves a variety of incubation times for
the light-sensitizing drug and a variety of light sources depending on the
target tissue. The basic premise of PDT is selective tissue destruction.
Although the photosensitizer may be absorbed all over by many cells, atypical or
cancerous cells take up more of the drug and retain the drug for a longer duration
than normal tissues.
At present, the primary limitation of available PDT techniques is the depth
of penetration of the light and ability to target cells within at most 1/3 of an
inch (approximately 1 cm) of the light source. Therefore, tumors or atypical
growths must be close to the surface of the skin or treatment surface for PDT to
work.
PDT is currently used in a number of
medical fields including oncology (cancer), dermatology (skin), and cosmetic
surgery.
In oncology, it is FDA approved for non-small cell lung cancer, esophageal
cancer, and precancerous changes of Barrett's esophagus. Its use is also being
further investigated through clinical trials in general oncology for conditions
including cancers of the cervix (mouth of uterus), prostate gland, brain, and
peritoneal cavity (the abdominal space that contains the stomach, liver, and
internal organs).
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| Levulan stick (photosensitizer medication) |
In dermatology, PDT with the photosensitizer Levulan Kerastick® (20% delta-aminolevulinic
acid HCl) is used for the treatment of pre-skin cancers called actinic keratosis
(AK). The initial approval was specifically for normal (non-hyperkeratotic)
actinic keratosis of the face and scalp with a specified 14- to 18-hour drug
incubation time, and 1,000 seconds (16 minutes and 40 seconds) of activation by
a blue light source. PDT is also used for acne, rosacea, skin cancer, sun
damage, cosmetic skin improvement, oily skin, enlarged sebaceous glands,
wrinkles, rejuvenation (anti-aging), warts, hidradenitis suppurativa, psoriasis,
and many other skin conditions. It is not used to remove moles or birthmarks.
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| Application of Levulan to the face |
Next: What photosensitizer drugs are available? »
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