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14 April 2014 Recovery of optical properties from interstitial spectroscopy for photodynamic therapy treatment planning
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Knowledge of optical properties is required to determine light dose in photodynamic therapy. We have designed an interstitial optical probe, consisting of six helically arranged side-firing fibers enclosed in a 1.1 mm diameter encapsulant, that can be used to determine these values. White light is delivered by one fiber and detected by the others. Based on a Monte Carlo (MC) model of the probe, the absorption (μa) and reduced scattering (μs') coefficients of the sample are determined. Recovery was verified in tissue-simulating phantoms containing MnTPPS or intact human erythrocytes as absorbers and Intralipid as scatterer. Mean errors in recovery of μa and μs' were 9% and 19%, respectively. In phantoms containing erythrocytes, hemoglobin oxygen saturation was recovered with mean error of 12%. Using the MC model, we mapped the volumes sampled by particular spectroscopy fibers. For μa = 0.1 cm-1 and μs' = 20cm-1, 49% of photon packets detected at the fiber adjacent to the source sampled a radius further than 5 mm from the probe, while 24% of photon packets sampled further than 7.5 mm. When μs' was reduced to 10 cm-1, 54% of photon packets traversed a radius greater than 5 mm from the probe and 29% sampled further than 7.5 mm. Changing the value of μa to 0.2 cm-1 did not have an effect on the sampled volume. We also provide a new probe design that aims to improve upon the accuracy of the current probe by incorporating a wider range of source-detector separations.
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Timothy M. Baran, Michael C. Fenn, and Thomas H. Foster "Recovery of optical properties from interstitial spectroscopy for photodynamic therapy treatment planning", Proc. SPIE 8931, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XXIII, 89310K (14 April 2014);

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