Biophysical changes such as inflammation and necrosis occur immediately following PDT and may be used to
assess the treatment response to PDT treatment in-vivo. This study uses localized reflectance measurements to quantify
the scatter changes in tumor tissue occurring in response to verteporfin-based PDT treatment in xenograft pancreas
tumors. Nude mice were implanted with subcutaneous AsPC-1 pancreatic tumors cells in matrigel, and allowed to
establish solid tumors near 100mm3 volume. The mice were sensitized with 1mg/kg of the active component of
verteporfin (benzoporphryin derivative, BPD), one hour before light delivery. The optical irradiation was performed
using a 1 cm cylindrical interstitial diffusing tip fiber with 20J of red light (690nm). Tumor tissue was excised
progressively and imaged, from 1 day to 4 weeks, after PDT treatment. The tissue sections were stained and analyzed by
an expert veterinary pathologist, who provided information on tissue regions of interest. This information was correlated
with variations in scattering and absorption parameters elucidated from the spectral images and the degree of necrosis
and inflammation involvement was identified.
Areas of necrosis and dead cells exhibited the lowest average scatter irradiance signature (3.78 and 4.07
respectively) compared to areas of viable pancreatic tumor cells and areas of inflammation (5.81 and 7.19 respectively).
Bilirubin absorbance parameters also showed a lower absorbance value in necrotic tissue and areas of dead cells (0.05
and 0.1 respectively) compared to tissue areas for viable pancreatic tumor cells and areas of inflammation (0.28 and
0.35). These results demonstrate that localized reflectance spectroscopy is an imaging modality that can be used to
identify tissue features associated with PDT treatment (e.g. necrosis and inflammation) that can be correlated with
histopathologically-reviewed H&E stained slides. Further study of this technique may provide means for automated
discrimination of tissue features based on scatter and absorbance maps elucidated from reflectance spectral datasets and
provide a valuable tool for treatment response monitoring during PDT and enabling more effective treatment planning.
These results are relevant to verteporfin-based PDT trial for treatment pancreatic cancer in non-surgical
candidate cases (VERTPAC-1 University College London, PI Pereira), where individualized assessment of damage and
response could be beneficial, if this study is proven to be a well-controlled imaging tool.