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PDT Dose Dosimetry for Pleural Photodynamic Therapy

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Y Ong

Y Ong*, M Kim , R Penjweini , J Finlay , A Dimofte , T Zhu , University of Pennsylvania, Philadelphia, PA


WE-RAM1-GePD-TT-3 (Wednesday, August 2, 2017) 9:30 AM - 10:00 AM Room: Therapy ePoster Theater

Purpose: To determine delivered PDT dose at multiple sites in the thoracic cavity during pleural photodynamic therapy from light fluence rate and photosensitizers fluorescence acquire simultaneously using the same isotropic detectors.

Methods: Patients with pleural mesothelioma was administered with Photofrin (Pinnacle Biologics, Chicago, IL, USA) at a dose of 2mg/kg of body weight 24 hours before treatment. PDT treatment was performed with 632nm light to a total fluence of 60 J/cm2. Eight isotropic detectors were used to collect light fluence data during treatment from eight locations within the pleural cavity. Four of the eight isotropic detectors were connected to light dosimeters and CCD spectrometers (Exemplar, B&W Tek, Inc., Newark, DE, USA) using bifurcated optical fibers to record light fluence rates and sensitizer fluorescence spectra simultaneously. Fluorescence spectra were fitted to the basis spectra of Photofrin, laser and Fourier components using single value decomposition fitting. Optical properties correction was applied to Photofrin fluorescence SVD to correct for the heterogeneity of optical properties of the surrounding tissues. The absolute Photofrin concentration was quantified by comparing the corrected Photofrin SVD to a calibration curve obtained from phantom with known Photofrin concentrations. PDT dose delivered to target tissue was calculated by taking the product of delivered light dose and mean Photofrin concentration.

Results: From the results of 8 patients and 22 sites, we observed large variation in the mean Photofrin concentration (1.13 to 10.75 mg/kg) among different pleural tissues and among different patients and the uncertainty of the measurements was 9.5%. PDT doses can be different by 4.2 times intra-patients and 9.4 inter-patients. Since the total light fluence is the same in all sites, the difference is entirely due to heterogeneity in photosensitizer concentration.

Conclusion: PDT dose delivered during PDT treatment could serve as a useful predictor of treatment outcome.

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