Photodynamic therapy (PDT) is a medical treatment that utilizes a photosensitizing molecule (frequently a drug that becomes activated by light exposure) and a light source to activate the applied drug. Very thin superficial skin cancers called actinic keratoses and certain other types of cancer cells can be eliminated this way. Acne can also be treated as well. 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. Occasionally, a photosensitizing molecule that is already part of the body can be activated. 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.
- application of photosensitizer drug
- incubation period
- light activation
Although first used in the early 1900s, PDT in the modern sense is a new, evolving science. Current PDT involves a variety of incubation times for different the light-sensitizing drugs and a variety of light sources depending on the target tissue. The basic premise of PDT is selective tissue destruction.
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.