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Quantitative Perfusion Measurement in Rectal Cancer Using Three Different Pharmacokinetic Models: Implications for Prospective Study Design

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K Nie

K Nie1, T Mao2 , L Shi2 , N Yue1 , S Jabbour1 , S Kim1 , X Hu2 , L Qian2 , X Sun2 , T Niu2* , (1) Rutgers-Cancer Institute of New Jersey, Rutgers-Robert Wood Johnson Medical, New Brunswick, NJ, USA (2) Sir Run Run Shaw Hospital, Institute of Translational Medicine, Zhejiang University, Hangzhou, Zhejiang, China


SU-F-R-34 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:To compare three different pharmacokinetic models for analysis of dynamic-contrast-enhanced (DCE)-CT data with respect to different acquisition times and location of region of interest.

Methods:Eight rectal cancer patients with pre-treatment DCE-CTs were included. The dynamic sequence started 4-10seconds(s) after the injection of contrast agent. The scan included a 110s acquisition with intervals of 40x1s+15x3s+4x6s. An experienced oncologist outlined the tumor region. Hotspots with top-5%-enhancement were also identified. Pharmacokinetic analysis was performed using three different models: deconvolution method, Patlak model, and modified Toft’s model. Perfusion parameters as blood flow (BF), blood volume (BV), mean transit time (MTT), permeability-surface-area-product (PS), volume transfer constant (Ktrans), and flux rate constant (Kep), were compared with respect to different acquisition times of 45s, 65s, 85s and 105s. Both hotspot and whole-volume variances were also assessed. The differences were compared using the Wilcoxon matched-pairs test and Bland-Altman plots.

Results:Moderate correlation was observed for various perfusion parameters (r=0.56-0.72, p<0.0001) but the Wilcoxon test revealed a significant difference among the three models (P < .001). Significant differences in PS were noted between acquisitions of 45s versus longer time of 85s or 105s (p<0.05) using Patlak but not with the deconvolution method. In addition, measurements varied substantially between whole-volume vs. hotspot analysis.

Conclusion:The radiation dose of DCE-CT was on average 1.5 times of an abdomen/pelvic CT, which is not insubstantial. To take the DCE-CT forward as a biomarker in oncology, prospective studies should be carefully designed with the optimal image acquisition and analysis technique. Our study suggested that: (1) different kinetic models are not interchangeable; (2) a 45s acquisition might not be sufficient for reliable permeability measurement in rectal cancer using Patlak model, but might be achievable using deconvolution method; and (3) local variations existed inside the tumor, and both whole-volume-averaged and local-heterogeneity analysis is recommended for future quantitative studies.

Funding Support, Disclosures, and Conflict of Interest: This work is supported by the National High-tech R&D program for Young Scientists by the Ministry of Science and Technology of China (Grant No. 2015AA020917), Natural Science Foundation of China (NSFC Grant No. 81201091).

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