Photodynamic therapy (PDT) is a photochemistry based cytotoxic technique that imparts cellular damage via excitation of a photosensitizer with drug-specific wavelength of light. The dose at the treatment site for type II PDT is determined by three factors: photosensitizer (PS) concentration, oxygenation status and delivered light irradiance. Most of the FDA approved photosensitizers in their triplet-excited state generate cytotoxic species by reacting with the ground state oxygen that is available in the surrounding environment. Given the inter- and intra-subject variability in the uptake of the photosensitizer and the distribution of oxygen in the tumor, understanding the interplay between these dose parameters could aid in determining photodynamic therapy efficacy. Previously several studies have discussed the interplay between the dose parameters using shown point measurements and 2D imaging systems. Using various subcutaneous and orthotopic mouse models we will demonstrate the utility of a non-invasive non-ionizing photoacoustic imaging modality to determine efficacy and predict treatment response in Benzoporphyrin derivative (BPD) or Aminolevulinic acid (ALA) based PDT. We further compare the predictive capability of photoacoustic imaging with the more predominantly used fluorescence imaging and immunohistochemistry techniques.

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Srivalleesha Mallidi, Zhiming Mai, Amjad P. Khan, and Tayyaba Hasan, "Predicting photodynamic therapy efficacy with photoacoustic imaging (Conference Presentation)," Proc. SPIE 9694, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XXV, 96940A (Presented at SPIE BiOS: February 13, 2016; Published: 26 April 2016); https://doi.org/10.1117/12.2217889.4848635783001.