Dr. Cole is board certified in dermatology. He obtained his BA degree in bacteriology, his MA degree in microbiology, and his MD at the University of California, Los Angeles. He trained in dermatology at the University of Oregon, where he completed his residency.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
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. Very thin superficial skin cancers called actinic keratoses and certain other types of cancer cells can be eliminated 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. Then light energy is applied selectively to the appropriate tissue.
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 dermatology, PDT with the photosensitizer Levulan Kerastick® (20% delta-aminolevulinic acid HCl) is used for the treatment of very early, thin skin cancers called actinic keratoses (AK). The initial approval was specifically for the treatment of actinic keratosis of the face and scalp with a combination of an application of the photosensitizer followed by a timed exposure to a special 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.
Porfimer sodium makes the skin and eyes sensitive to light for approximately 6 weeks after treatment. Thus, patients are advised to avoid direct sunlight and bright indoor light for at least 6 weeks.
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.
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