(PDT, photoradiation therapy, phototherapy, photochemotherapy) 1. a treatment for some types of superficial cancers. A light-sensitive agent (porfimer sodium [Photofrin] or temoporfin [Foscan]) is injected into the bloodstream and remains in cancer cells for a longer time than in normal cells. Exposure to laser radiation produces an active form of oxygen that destroys the treated cancer cells. The laser radiation can be directed through a fibreoptic bronchoscope into the airways, through a gastroscope into the oesophagus, or through a cystoscope into the bladder. PDT causes minimal damage to healthy tissue, but as it cannot pass through more than about 3 cm of tissue, it is restricted to treating tumours on or just under the skin or on the lining of internal organs. Photodynamic therapy makes the skin and eyes sensitive to light for six weeks or more after treatment. 2. a treatment for wet age-related *macular degeneration that involves the intravenous injection of a light-sensitive agent (verteporfin, Visudyne) which passes to the abnormal leaking blood vessels in the retina. The agent is activated when a cold laser light is directed at the macula, sealing the abnormal vessels and thus preventing further leakage and macular damage. The effect is to limit visual loss and stabilize vision.... photodynamic therapy
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