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Photodynamic therapy (PDT), sometimes called photochemotherapy, is a form of phototherapy using nontoxic light-sensitive compounds that are exposed selectively to light, whereupon they become toxic to targeted malignant and other diseased cells (phototoxicity). PDT has proven ability to kill microbial cells, including bacteria, fungi and viruses. PDT is popularly used in treating acne. It is used clinically to treat a wide range of medical conditions, including wet age-related macular degeneration and malignant cancers,〔 〕 and is recognised as a treatment strategy which is both minimally invasive and minimally toxic. Most modern PDT applications involve three key components:〔 a photosensitizer, a light source and tissue oxygen. The combination of these three components leads to the chemical destruction of any tissues which have both selectively taken up the photosensitizer and have been locally exposed to light. The wavelength of the light source needs to be appropriate for exciting the photosensitizer to produce reactive oxygen species. These reactive oxygen species generated through PDT are free radicals (Type I PDT) generated through electron abstraction or transfer from a substrate molecule and highly reactive state of oxygen known as singlet oxygen (Type II PDT). In understanding the mechanism of PDT it is important to distinguish it from other light-based and laser therapies such as laser wound healing and rejuvenation, or intense pulsed light hair removal, which do not require a photosensitizer. ==Procedure== In order to achieve the selective destruction of the target area using PDT while leaving normal tissues untouched, either the photosensitizer can be applied locally to the target area, or photosensitive targets can be locally excited with light. For instance, in the treatment of skin conditions, including acne, psoriasis, and also skin cancers, the photosensitizer can be applied topically and locally excited by a light source. In the local treatment of internal tissues and cancers, after photosensitizers have been administered intravenously, light can be delivered to the target area using endoscopes and fiber optic catheters (see figure). Photosensitizers can also target many viral and microbial species, including HIV and MRSA.〔 〕 Using PDT, pathogens present in samples of blood and bone marrow can be decontaminated before the samples are used further for transfusions or transplants.〔 〕 PDT can also eradicate a wide variety of pathogens of the skin and of the oral cavities. Given the seriousness that drug resistant pathogens have now become, there is increasing research into PDT as a new antimicrobial therapy.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「photodynamic therapy」の詳細全文を読む スポンサード リンク
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