Photo Dynamic Therapy or Blue-Light therapy
Photodynamic Therapy (PDT) is the combination of light and light sensitive
agents (such as porphyrins) in an oxygen-rich environment. The treatment 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.
How does PDT work?
PDT works by direct injury to the target cells and tissues. This involves an
activated oxygen molecule that can injure or destroy nearby cells. By
preferentially attacking the active or abnormal cells, PDT combines a very high
success rate with good preservation of normal
significant risks for
Once the areas have healed following PDT, the areas are reexamined to see if
additional treatments or biopsies are needed.
PDT essentially has three steps:
- Application of photosensitizer drug
- Incubation period
- Light activation
PDT is currently used in a number of medical fields including
dermatology (skin), and
surgery. 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). 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
skin cancer, sun
damage, cosmetic skin improvement,
enlarged sebaceous glands,
(anti-aging), warts, hidradenitis suppurativa,
psoriasis, and many
other skin conditions. It is not used to remove
moles or birthmarks.
Photodynamic therapy (PDT) is recommended for the treatment of wet age-related
degeneration for individuals who have a confirmed diagnosis of
classic with no occult subfoveal choroidal neovascularisation (CNV)
(that is, whose lesions are composed of classic CNV with no evidence of an
occult component) and best-corrected visual acuity 6/60 or better. PDT should be
carried out only by retinal specialists with expertise in the use of this
How is PDT used to treat cancer?
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.
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. In addition, PDT may activate the
immune system to attack the tumor cells.
How is recovery?
Recovery is usually fairly easy and uneventful. Many patients have mild dryness
and a faint to mild sunburn of the treated area. A small percent of patients may
have moderate or marked discomfort and a harder recovery because of more
skin dryness, redness, or
Researchers continue to study ways to improve the effectiveness of PDT and
expand it to other cancers. Clinical trials (research studies) are under way to
evaluate the use of PDT for cancers of the brain, skin, prostate, cervix, and
peritoneal cavity (the space in the abdomen that contains the intestines,
stomach, and liver).
For more information on photodynamic therapy,