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Title: SU-D-16A-07: Photobleaching Predicts Necrosis in Interstitial PDT

Purpose: Dosimetry for PDT has proven to be a challenge thus far, and for prediction of PDT outcome, a singlet oxygen model based on fundamental photophysical parameters has been developed. Previously, the photobleaching effect of photosensitizers was taken into account in the singlet oxygen explicit dosimetry model; here we report of direct measurements of photobleaching in the same model to assess the conditions under which implicit dosimetry using photobleaching can serve as an intermediate surrogate for PDT damage. Methods: Fluorescence spectra were measured interstitially in sensitized mouse tumors prior to after irradiation via a cylindrical diffuser. Photobleaching was determined by the relative decrease in fluorescence amplitude from the initial pre-treatment measurement. Spectra were analyzed by singular value decomposition to determine the photosensitizer concentration. Different photosensitizers were used to see the effect of photobleaching on PDT outcome and the impact of fluence on photobleaching. The drugs used were BPD (at two drug-light intervals), HPPH, and Photofrin. PDT outcome was determined by tumor necrosis radii measured upon sectioning and staining of treated tumors. Results: Post-PDT photosentizer concentrations were compared to initial pre-PDT photosensitizer concentrations, and the decrease was greater with a higher fluence measured during treatment. Furthermore, photobleaching and necrosis radius weremore » found to be positively correlated. The relationship between photobleaching and necrosis radius is sensitizer-dependent, however the differences among sensitizers can be understood in terms of their respective photophysical parameters. Conclusions: Photobleaching is predictive of PDT outcome, but a comprehensive singlet oxygen model, has the potential to further improve the prediction of PDT outcome and the understanding of implicit dosimetry.« less
Authors:
; ; ;  [1]
  1. University of Pennsylvania, Philadelphia, PA (United States)
Publication Date:
OSTI Identifier:
22333969
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 41; Journal Issue: 6; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; CONCENTRATION RATIO; DOSIMETRY; FLUORESCENCE; FLUORESCENCE SPECTROSCOPY; IRRADIATION; MICE; NECROSIS; NEOPLASMS; SENSITIZERS