MicroPET-CT evaluation of interstitial brachytherapy in pancreatic carcinoma xenografts

Abstract

Interstitial brachytherapy (IBT) has been introduced as treatment for unresectable pancreatic cancers to maximize local dose and minimize irradiation of surrounding normal tissue. MicroPET-CT systems provide excellent anatomic and molecular information. To use 18F-FDG micro-positron emission tomography (PET)/computed tomography (CT) to evaluate the therapeutic effect of (125)I interstitial brachytherapy on transplantation tumor of human pancreatic carcinoma in Balb/c-nu mice. Xenograft models were created by subcutaneous injection of Swl990 human pancreatic cancer cell suspensions into the immunodeficient Balb/c-nu mice. The study was randomly divided into three groups: control group (n = 6), empty seed implant group (n = 6), and (125)I seed implant group (n = 6), respectively. Before and 1 week after treatment, 18F-FDG microPET-CT scan was performed. In-vivo cell proliferation and apoptosis were monitored by thymidine kinase 1 (TK1) immunostaining and Dutp-biotin nick end labeling (TUNEL) assay. Our results showed that before treatment the SUVmax and SUVmean values among three groups had no significant statistical difference. One week after treatment the SUVmax and SUVmean in (125)I seed implant group were significantly lower than before, while for the empty seed group and control group there were no significant difference compared with before treatment. Immunohistochemical analysis of tumor tissue revealed significantly less TK1 positive cells in (125)I seed implant group than in empty seed group and control group. The index of apoptosis was slightly higher in (125)I seed implant group than in empty seed group and control group as evaluated by TUNEL assay. These results suggest that 18F-FDG microPET-CT may be useful as a non-invasive imaging modality to assess early response to (125)I seed brachytherapy in a pancreatic carcinoma Xenograft.