Four-channel PDT dose dosimetry for pleural photodynamic therapy

We have developed a four-channel PDT dose dosimetry system to simultaneously acquire light dosimetry and sensitizer fluorescence data from four sites in the thoracic cavity during pleural photodynamic therapy (PDT). Photosensitizer fluorescence emitted during PDT is of interest for the monitoring of local concentration of the photosensitizer and its photobleaching. However, the variation in tissue optical properties will cause the photosensitizer fluorescence to alter. Optical properties correction to the measured fluorescence is required for absolute quantification of photosensitizer concentration. In this study, we determine an empirical optical properties correction function using Monte Carlo (MC) simulations of fluorescence for a range of physiologically relevant tissue optical properties. Optical properties correction factors for Photofrin fluorescence were determined experimentally using the same empirical function to recover the Photofrin concentration from measured fluorescence during PDT. The results showed no photobleaching of Photofrin during the course of PDT. PDT doses delivered to multiple sites in the thoracic cavity of 4 patients were presented and showed that PDT dose can be different by 4.4 times intra-patients and 9.1 times inter-patients.