Diffusion-Weighted and Dynamic Contrast-Enhanced MRI Derived Imaging Metrics for Stereotactic Body Radiotherapy of Pancreatic Ductal Adenocarcinoma: Preliminary Findings

We aimed to assess longitudinal changes in quantitative imaging metric values obtained from diffusion-weighted (DW-) and dynamic contrast-enhanced magnetic resonance imaging (DCE)-MRI at pre-treatment (TX [0]), immediately after the first fraction of stereotactic body radiotherapy (D1-TX[1]), and 6 weeks post-TX (Post-TX[2]) in patients with pancreatic ductal adenocarcinoma. Ten enrolled patients (n = 10) underwent DW and DCE-MRI examinations on a 3.0 T scanner. The apparent diffusion coefficient, ADC (mm(2)/s), was derived from DW imaging data using a monoexponential model. The tissue relaxation rate, R-1t, time-course data were fitted with a shutter-speed model, which provides estimates of the volume transfer constant, K-trans (min(-1)), extravascular extracellular volume fraction, v(e), and mean lifetime of intracellular water protons, tau(i) (seconds). Wilcoxon rank-sum test compared the mean values, standard deviation, skewness, kurtosis, and relative percentage (r, %) changes (Delta) in ADC, K-trans, v(e), and tau(i) values between the magnetic resonance examinations. rADC(Delta 2-0) values were significantly greater than rADC(Delta 1-0) values (P = .009). rK(trans) Delta(2-0) values were significantly lower than rK(trans) Delta(1-0) values (P = .048). rv(e Delta 2-1) and rv(e Delta 2-0) values were significantly different (P = .016). r tau(i Delta 2-1) values were significantly lower than r tau(i Delta 2-0) values (P = .008). For group comparison, the pre-TX mean and kurtosis of ADC (P = .18 and P = .14), skewness and kurtosis of K-trans values (P = .14 for both) showed a leaning toward significant difference between patients who experienced local control (n = 2) and failed early (n = 4). DW- and DCE-MRI-derived quantitative metrics could be useful biomarkers to evaluate longitudinal changes to stereotactic body radiotherapy in patients with pancreatic ductal adenocarcinoma.