SU‐E‐T‐215: Tissue Optical Properties Determination in PDT Treated Head & Neck Patients Using a Balloon Diffusing Light Source

Abstract

Purpose: The main objective of this study was to determine the optical properties (scattering and absorption coefficients) in vivo by interstitial measurements using a light detection device made for this purpose. Methods: Patients were enrolled in a phase I dose escalation study of photodynamic therapy for the treatment of pre‐malignant tumors and superficial microinvasive disease of the head and neck. Patients were given the photosensitizer Levulan orally followed by the administration of red light (629–635 nm) to the tumor from a laser to a dose of 50–200 J/cm2. Because of technical challenges, some of the patients were not able to be treated using the classic microlens fiber and instead used a translucent diffusing balloon catheter to deliver the light. Measurements were performed using a light detection device before and after light treatment delivery. The detector is scanned along the length of the light source containing catheter. Scans are done with the device placed on the treatment area and on the normal oral cavity tissue. Optical properties of both the normal and diseased tissue before and after the light treatment were obtained and compared to those measured with a fiber‐optic probe. The fiber‐optic based probe was placed on the tissue surface, and white light was delivered to the tumor surface by one of its source fibers. The diffusely reflected white light was collected by a spectrograph and analyzed to determine the absorption and scattering spectra of the tissue. Results: A theory based on light source on semi‐infinite medium has been developed to interpret the measured data. Results from both methods were compared for accuracy. This model was also validated by measurements performed in tissue‐simulating. Conclusions: We developed a model for quick and accurate determination of tissue optical properties in semi‐infinite medium, which is theoretically suitable for determination of optical properties head and neck PDT. Conclusions: