Comparison between isotropic and nonisotropic dosimetry systems during intraperitoneal photodynamic therapy

Background and Objective: On-line monitoring of light fluence during intrap eritoneal photodynamic therapy (IP PDT) is crucial for safe light delivery. A flat photodiode-based dosimetry system is compared with an isotropic det ector-based system in patients undergoing IP PDT. Study Design/Materials and Methods: Flat photodiodes and spherical detector s were placed side by side in the abdomen, for simultaneous light dosimetry in 19 patients. Tissue phantom experiments were performed to provide a pre liminary estimate of the tissue optical properties of the peritoneum. Results: The conversion factor between systems for 630-nm light was found t o be 1.7 +/- 0.12. The mu(eff) of the tissues in the abdomen is estimated t o vary between 0.5 cm(-1) to 1.4 cm(-1) assuming a mu(s)' = 7 cm(-1). Conclusions: The measured conversion factor should allow for comparison of light fluences with future clinical protocols that use an isotropic-based d etector system. Differences in the optical properties of the underlying tis sues may contribute to the variability in light measurements. Lasers Surg. Med. 26:292-301, 2000. (C) 2000 Wiley-Liss, Inc.