How to avoid local side effects of bladder Photodynamic Therapy: The impact of fluence rate
Résumé
Purpose: To avoid irritative bladder symptoms following bladder photodynamic therapy such as urgency, frequency and pain, which are associated with inflammation and destruction of normal urothelium. Material and Methods: Rats bearing orthotopic bladder tumors were instilled with hexyl-aminolevulinate and illuminated with red light at high (100 mW/cm²) or low (15 mW/cm²) fluence rate. Cystectomy specimens 48 hours after treatment were subjected to anatomopathological examination and evaluation of inflammatory reaction and apoptosis. In vivo photobleaching was assessed during illumination at both fluence rates. Results: All superficial tumors were eradicated, irrespective of the light dose and fluence rate. High fluence rates induced necrosis with inflammatory reaction and absence of normal urothelium. Low fluence rates did not provoke inflammation and resulted in apoptotic cell death, with preservation of urothelial integrity. This can be attributed to the faster photobleaching of the photosensitizer in normal urothelium at low fluence rates. Conclusions: Bladder photodynamic therapy at low fluence rate minimizes side effects without hampering therapeutic efficacy.