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New balloon catheter system used for PDT in the human urinary bladder: accuracy of light distribution

Photodynamic therapy (PDT) may provide a new approach for treatment of patients with superficial transitional carcinoma and carcinoma in situ of the bladder. The light applicator for the bladder wall (Rusch) is constructed as a balloon catheter with two concentric balloons. A new PDT applicator (Rusch) was assessed for the homogeneity and accuracy of irradiation during PDT. In an in-vitro experiment with 17 freshly harvested porcine bladders the fluence rate was measured locally with isotropic detectors. The results were compared to the light fluence detected by the PDT applicator. The increase of the fluence rate (beta) inside the bladders due to back scattering ranged between 5.3 and 7.0 with an average of 6.2. Local variations of the fluence rate in the spherical bladders were also smaller than 15%. Therefore it is concluded, that a homogeneous and accurate irradiation during PDT is possible. Blood between the outer balloon and the bladder wall reduces the local fluence rate strongly and should to be avoided. Also larger air bubbles in the applicator can lead to an inhomogeneous light distribution. In regular application the presented new catheter system provides accurate and easy light dosimetry during PDT of the bladder. Attention had to be paid to a continuous flushing of the space between balloon and bladder wall in order to prevent the accumulation of urine and blood. To avoid a malfunction of the system and large errors in light dosimetry and application, it is advisable to monitor the measured light dosage and the shape of the balloon using ultrasonography during PDT.