Clinical Application of Photodynamic Therapy

摘要

Photodynamic therapy(PDT) is a new medical technology, the study on photodynamic therapy was in full swing in the past two decade. Scientists have made great progress in it. Photosensitizer,oxygen and light source play important role in photodynamic therapy.PDT is a light activated chemotherapy. A photon is adsorbed by a photosensitizer 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 cell begins to die.Photodynamic therapy allows selective treatment of localized cancer. PDT involves administration of a photosensitizer to the patients, followed by delivery of light to the cancerous region. The light activates the agent which kills the cancer cells. Without light,the agent is harmless.As a new therapy,photodynamic Therapy has great Advantage in treating cancers. 1. PDT avoids systemic treatment. The treatment occurs only where light is delivered, hence the patient does not undergo go needless systemic treatment when treating localized disease. Side-effects are avoided, from losing hair or suffering nausea to more serious complications. 2. PDT is selective. The photosensitizing agent will selectively accumulate in cancer cells and not in surrounding normal tissues.Hence ,there is selective targeting of the cancer and sparing of surrounding tissues.3. when surgery is not possible. PDT kills cancer cells but does not damage collagenous tissue structures,and normal cells will repopulate these structures. Hence,if a patient has cancer in a structure that cannot be removed surgically(eg. ,the upper bronchi of the lung) ,PDT can still treat the site. 4. PDT is repeatable. Unilke radiation therapy, PDT can be used again and again. Hence,it offers a means of longterm management of cancer even if complete cure is not attainable.