Photodynamic Therapy (PDT) was primarily called Photo radiation Therapy (PRT), Photochemical Therapy (PCT). It is a promising novel therapeutic method for diagnosis and treatment of many tumors, utilizing a photosensitizer, visible light and oxygen to produce singlet oxygen and other reactive oxygen species. Photons are absorbed by a photosensitive drug which moves the drug into an excited state. The excited drug can then pass its energy to oxygen to create a chemical radical called "singlet oxygen". Singlet oxygen attacks cellular structures by oxidation. Such oxidative damage might be oxidation of cell membranes or proteins. When the accumulation of oxidative damage exceeds a threshold level, the tumor cells begin to die.

Advantages of PDT over Conventional Treatments of Cancer

Treatment with PDT consists of a four-step process:

Stage 1  Intravenous injection (I.V.) or topical application of a photosensitising agent.

Stage2   Permit time for systemic porphyrins (I.V. injection) to be cleared from normal tissues and be preferentially retained by rapidly growing tissues (e.g., cancer or psoriasis), or for topical porphyrins to be absorbed by the skin before illumination with a certain wavelength laser light within a period of time. If necessary, take a second light application.

Stage3   To develop the cytotoxic effect of the pharmaceutical, the non-thermal laser illumination activates the photosensitizer in a targeted fashion within the tissue to be treated．The subsequent phototoxic reactions result in the locally restricted death of the tumor cells. The light application is performed either from outside or endoscopically via optical fibers.

Stage 4   The necrotic target tissue is destroyed and eliminated after a certain period of time.