PHOTODYNAMIC THERAPY ON RAT URINARY-BLADDER WITH INTRAVESICAL INSTILLATION OF 5-AMINOLEVULINIC ACID - LIGHT DIFFUSION AND HISTOLOGICAL-CHANGES

Purpose: Photodynamic therapy (PDT) has the potential to treat extensi ve premalignant lesions and microinvasive tumors in the bladder, but i ts use has been hampered by the risk of detrusor muscle damage and pro longed skin photosensitivity. We have shown that the rat urothelium ca n be sensitized by selectively using a 10% solution of 5-aminolevulini c acid (ALA) at pH 5.5 administered intravesically. This paper evaluat es the photodynamic effects on sensitized bladders. Materials and Meth ods: The bladders of Wistar rats were instilled with ALA solutions of different concentrations at pH 5.5 and subsequently treated with laser light at 630 nm. Bladders were harvested 1 to 7 days after PDT for hi stological assessment. Results: Under optimum conditions (10% intralip id diffusion medium, light dose 50J) uniform urothelial necrosis was s een after 1 to 2 days; it healed in 7 days without damage to the under lying muscle layer although some increase in collagen was seen in the lamina propria. Overtreatment or poor light distribution resulted in m uscle necrosis and scarring. Conclusions: Selective urothelial necrosi s is possible with PDT using intravesical ALA. There is now sufficient data for pilot clinical trials to start photodynamic therapy for mana gement of superficial bladder cancer or carcinoma in situ.