ONLINE MEASUREMENT AND MODEL BASED DOSIMETRY OF PDT

Massachusetts General Hospital, Boston MA

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Abstract

APPLICANT'S DESCRIPTION: (Provided by Applicant) Photodynamic therapy dosimetry is largely based upon empirical dose escalation trials without much attention paid to the individual variations between patients. This study uses basic laboratory measurements and modeling studies to design and develop fundamentally new dosimetry instrumentation which directly measures the pertinent parameters for optimal PDT treatment outcome. Specifically, we will develop (I) accurate in vivo photosensitizer concentration measurement via micro-probing the fluorescence, (ii) quantitative PS imaging, (iii) methods for measuring the PS aggregation fraction by combining fluorescence and acoustic optical spectroscopy, and (iv) a co-localized blood flow and oxygen tension measurement system for micro- sampling of tissue before and after PDT. By designing our instruments based upon modeling studies together with basic microscopic measurements on tumor tissue, we are able to design new system combinations which have optimal signal to noise ratio, and sample the bulk tissue in a manner where the signal is readily interpreted. Secondly, by confirming that these measurements are directly correlated to measurable treatment outcomes, we demonstrate their utility. Lastly, by demonstrating that the inter-animal variability in tumor regrowth can be minimized, we demonstrate that these online dosimetry tools can improve the efficacy of treatment. The animal-tumor model used in this study will be the LNCaP prostate tumor grown subcutaneously in SCID mice, to match the program emphasis on epithelial disease. Similarly the photo- sensitizers are chosen match the program emphasis on using clinically approved molecules, with a particular focus on benzoporphyrin derivative (BPD) and aminolevulinic acid-induced protoporphyrin-IX (ALA-PPIX). A central theme in this project is to examine how the time-scale of the treatment affects the localization of photosensitizer and the resulting site of photodynamic action, and thereby the deposited dose. Both tumor regrowth assay and pathology endpoints will be used to determine which dosimetry tools are useful for which PS, and under which irradiation conditions they should be used for the optimal effect.