Early therapy monitoring of 125 I seed interstitial implant in a pancreatic cancer xenograft by 18 F-FDG Micro-PET/CT

Abstract

Objective To investigate the application value of early evaluation and monitoring of 125I interstitial implantation in a pancreatic cancer xenograft. Methods Xenograft models were created by subcutaneous injection of Sw 1990 human pancreatic cancer cell suspensions into the right hind limbs of the immunodeficient BABL/c nude mice. The tumors size were about 8-10 mm after two weeks. The mice were randomly divided into 5 groups, including control group （ n = 4）, empty seed implantation group （ n = 4） and 125I implantation group （n = 4）. Before treatment and one week after treatment, 18F-FDG Micro-PET/ CT scan was performed and then maximum standardized uptake values （SUVmax）, mean standardized uptake values （SUV ）, tumor size and necrosis rate were measured. HE staining and TK1 immunohistochemistry examination were carried out in the paraffin-embedded sample. Results Before treatment the SUVx and SUV values of three groups did not reach statistical significance. One week after treatment the SUVmax and SUV values of three groups were 3.53 ± 1.20 and 0. 57 ± 0.26 vs. 3.83 ±2.13 and0.59 ± 0.24vs. 0.29± 0.23 and0.016 ±0.001, respectively, with a significant difference （F =7.62,P =0. 01 ; F = 10. 34, P =0. 005）. The SUVmax and SUV values of 125I implant group were significantly lower than empty seed implant group and control group and were significantly lower than before treatment. Before treatment, tumor necrosis rate of three groups were not significantly different. Immunohistochemical staining found the TK1 positive staining index of three groups were respectively（64. 25 ± 1.71 ） % , （62. 25 ± 2.22） % and （38.25 ± 1.71 ） % with statistically significant difference （F =233.67, P 〈 0. 001 ）. The TK1 positive staining index of 125I implant group was significantly lower than empty seed implant group and control group. The SUVmax values had some positive correlation with TK1 positive staining index （ r = 0. 85,P = 0. 001 ）. Conclusions is F-FDG Micro-PET/CT may be useful as a noninvasive imaging modality to assess early response to 125I seed brachytherapy in a pancreatic cancer xenograft. Key words: 125I seed; Brachytherapy; Pancreatic cancer; Micro-positron emission tomography and computed tomography （Micro-PET/CT） ; Computed tomography （CT） ; is Fluorine- fluorinedeoxyglucose （ is F-FDG ）