The morphological changes in rat bladder after photodynamic therapy with 5‐aminolaevulinic acid‐induced protoporphyrin IX

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Abstract
Objective To assess the optimum light energy needed to induce only superficial bladder wall damage during photodynamic therapy (PDT) as a treatment for bladder cancer. Materials and methods The urinary bladder (with normal epithelium) of 64 female rats was treated with PDT using a continuous‐wave argon‐ion laser as an energy source and aminolaevulinic acid (ALA)‐induced protoporphyrin IX photosensitizer. Four hours after the intravenous administration of ALA (300 mg/kg) the bladders were intravesically exposed to light fluences of 20–80 J/cm2. The control rats received no ALA and were exposed to 20 J/cm2 light. After 1, 3, 7 and 21 days the animals were killed and the morphological changes in bladder wall analysed both macroscopically and using light and scanning electron microscopy. Results At the dose of ALA given, a fluence of 20–40 J/cm2 caused mainly superficial damage, whereas 80 J/cm2 produced full‐thickness injuries to the bladder wall. The maximum effect of PDT occurred after 1 and 3 days of irradiation. After 3 weeks of PDT the histology showed few full‐thickness injuries and only in those treated with 80 J/cm2 light. Conclusion These results indicate that PDT can be used to safely induce a selective superficial removal of bladder mucosa with no fibrotic effects on detrusor musculature, when optimum photosensitizing drug and fluences are used. These findings support the use of PDT in the therapy of superficial bladder cancer.