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  • Standard products such as StockerYale's line lights and area lights have been combined, with and without modifications, to build illumination solutions for PDT and other dermatological applications.

Photodynamic Therapy (PDT)

Photodynamic Therapy (PDT) is a rapidly growing area of medical treatment. The diseases that can be successfully treated by PDT include skin cancer, brain tumors, tumors under the surface of the skin, and tumors located on the lining of internal organs. PDT is less invasive than other therapies and often produces a better cosmetic outcome, with little or no scarring.

Photodynamic Therapy involves the use of light-activated dyes (photosensitizers) that localize in target cells (e.g. in tumors) but not in normal, healthy cells. Photosensitizers utilize energy from treatment light to produce a cytotoxic oxygen species which kills cancerous or diseased cells. This toxic oxygen species is not a radical but is actually an excited state of oxygen. The excited state is more reactive than usual oxygen, and the atoms are in a different quantum spin state than is normally the case.

Several photosensitizer agents (either FDA-approved or currently under study) have been identified for use in PDT. Typically, these substances are injected intravenously into the diseased area. A few hours after injection, the photosensitizer has selectively accumulated in the tumor region. Because blood and melanin are relatively absorptive in the shorter visible wavelengths, it is preferable to use infrared light. Therefore, the ideal photosensitizer has an absorbance peak in the infrared part of the spectrum. This ensures that light used in the treatment is able to penetrate maximally through healthy tissue to arrive at the tumor.

Light-emitting diodes (LEDs) are considered an appropriate light source for PDT. LEDs have a relatively narrow bandwidth (usually 20 to 30 nm), and are available in a wide range of wavelengths, including the near infrared (NIR) and infrared (IR) -- from 650 nm to 950 nm. The flexibility provided by chip-on-board techniques makes it possible to fabricate customized LED illuminators for various PDT applications.

In more established Photodynamic Therapy treatments, such as skin cancer therapy, the diseased zone is exposed to an LED area light for a precisely calculated exposure time. In newer or more experimental areas of treatment, miniature LED arrays are actually implanted into tissue, or are placed on catheters and are moved through the body. In some procedures, LED dice are fixed to a flexible, compact substrate.

Because of their inherent compactness, LED illumination techniques often prove to be highly amenable to an effective solution. They also can turn out to be less expensive than laser-based approachs. The coherence and extreme monochromaticity of lasers are not necessary in this particular field of applications.

Moreover, since PDT does not require short sub-microsecond pulses, the rapid response of lasers is not necessary.

Variations on Photodyanmic Therapy and other dermatological applications for LEDs merit mention here. These include treatments for acne, psoriasis and scarring. Moreover, NASA has been experimenting with the use of LED light for healing wounds during space missions. (See for instance the article by Whelan et al, ''The NASA Light-Emitting Diode Medical Program -- Progress in Space Flight and Terrestrial Applications,'' NASA Marshall Space Flight Center.)