Assessment of biophysical tumor response to PDT in pancreatic cancer using localized reflectance spectroscopy

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 100mm(3) 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.