Rationale and Objectives
It was hypothesized that perfusion computed tomography (CT), blood flow (BF), blood volume (BV), and vascular permeability surface area (PS) product parameters would be predictive of therapeutic anticancer agent uptake in pancreatic cancer, facilitating image-guided interpretation of human treatments. The hypothesis was tested in an orthotopic rabbit model of pancreatic cancer, by establishing the model, imaging with endoscopic ultrasound (EUS) and contrast CT, and spatially comparing the perfusion maps to the ex vivo uptake values of the injected photosensitizer, verteporfin.
Materials and Methods
Nine New Zealand white rabbits underwent direct pancreas implantation of VX2 tumors, and CT perfusion or EUS was performed 10 days postimplantation. Verteporfin was injected during CT imaging, and the tissue was removed 1 hour postinjection for frozen tissue fluorescence scanning. Region-of-interest comparisons of CT data with ex vivo fluorescence and histopathologic staining were performed.
Results
Dynamic contrast-enhanced CT showed enhanced BF, BV, and PS in the tumor rim and decreased BF, BV, and PS in the tumor core. Significant correlations were found between ex vivo verteporfin concentration and each of BF, BV, and PS.
Conclusions
The efficacy of verteporfin delivery in tumors is estimated by perfusion CT, providing a noninvasive method of mapping photosensitizer dose.
The 5-year survival of pancreatic adenocarcinoma is approximately 3%, among the most dismal prognoses in all of oncology . Radical resection with or without adjuvant or neoadjuvant treatment is the only means of improving long-term survival but is only an option in approximately 25% of patients . For locally advanced and unresectable disease, a main focus of patient management is the preservation of an acceptable quality of life for as long as possible through palliative therapy . Treatments with minimal side effects that are able to provide some degree of tumor control are preferred in these cases, but options are currently limited. New therapeutic options—including photodynamic therapy (PDT) , radiofrequency ablation , tumor vaccines , and targeted nanoparticles —may be treatment options for unresectable pancreatic cancer, and the advance of suitable preclinical animal models will be critical to the development and implementation of each to accurately assess their efficacy before widespread clinical translation. For example, in a recent phase I/II study, verteporfin-based PDT was delivered to locally advanced pancreatic cancer . Although PDT was clearly able to induce a dose–dependent damage to the cancers, it was also noted that the treatment induced a necrotic volume that was inversely related to the observed contrast computed tomography (CT) enhancement . Beyond this, it is well known that drug permeability in cancer is directly related to perfusion in a number of cancer and drug combinations , and so, perfusion imaging is a reasonable way to diagnostically assess the penetration of therapeutics into the lesion. The goal of this study was to use a rabbit orthotopic model of cancer in the pancreas, and use it with conventional ultrasound and CT imaging to characterize the uptake and dose delivery of verteporfin to better understand the role of this type of imaging in human PDT treatments.
PDT is an alternative treatment for cancer, which uses the interaction of light and a photosensitizer, in the presence of oxygen, to produce singlet oxygen . The singlet oxygen causes direct cell death through necrosis , as well as indirect cell death by vascular damage–induced hypoxia. A major benefit of PDT is that it exerts its effect photochemically, rather than thermally; so, connective tissues such as collagen and elastin remain intact, preserving the mechanical integrity of the tissue . The photosensitizer drug, such as verteporfin used in this study, is most often delivered intravenously. Localized tissue necrosis can be produced by delivering light from a low-power laser directly to the tumor through a small diameter fiber . Because both drug delivery and light delivery affect the volume of tumor necrosis, dynamic CT imaging is proposed for planning and evaluating PDT treatment in pancreatic cancer.
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Materials and methods
Animal Experiment
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Image Acquisition
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Computed Tomography Analysis
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Ex Vivo Fluorescence Imaging and Histopathology
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Statistical Analysis
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Results
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Discussion
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Conclusions
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Acknowledgments
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