Performance evaluation of cylindrical fiber optic light diffusers for biomedical applications

Background and Objectives: Dosimetry for intracavity and interstitial light delivery requires next to the knowledge of tissue optical properties and models describing light propagation in tissue also exact knowledge of the spatial light source emission characteristics. However, the emission characteristics of cylindrical diffusers are often ill defined by the manufacturer, and not regularly determined by the end user, thus limiting the attainable dosimetry accuracy. Study Design/Materials and Methods: Commercial cylindrical diffusers, with active diffusive lengths of 12 cm and outer diameters of less than or equal to1 mm, were evaluated regarding their photometric emission characteristics. In addition to traditional tests of homogeneity such as light intensity emitted along the diffuser length and around its circumference (polar angle), azimuth emission was also measured. Results: It was demonstrated that the light emission distribution is specific to the diffuser manufacturer, and while good polar isotropy is often attained, azimuth isotropy can vary by more than a factor of 5. In hollow organs the latter can result in over treatment of tissue distal to the actual placement of the cylindrical diffusers. Conclusions: To enable light dosimetry and treatment planning for applications such as photodynamic therapy or interstitial laser hyperthermia or photocoagulation, standardization of emission properties reporting for optical fiber diffusers is required. (C) 2004 Wiley-Liss, Inc.