Intravoxel Incoherent Motion (IVIM) Magnetic Resonance Imaging (MRI) for Assessment of Treatment Response in Pancreatic Cancer

Abstract

Intravoxel Incoherent Motion (IVIM) Magnetic Resonance Imaging (MRI) is an emergent technique used to quantify diffusion and perfusion without the use of contrast agent. Our objective was to evaluate changes in IVIM parameters pre- and post-Radiation Therapy (RT) / chemotherapy in Pancreatic Ductal Adenocarcinoma (PDAC) patients to correlate these parameters and their changes with tumor radiation response. Pre- and post-treatment IVIM scans were acquired from 12 patients (median age: 70 [41-83]) with PDAC treated with RT (median: 98 [39-116] Gy BED) and chemotherapy. CA19-9 was used as a surrogate of radiation response and its validity was confirmed using the Kaplan-Meier method and the log-rank test. The Diffusion Weighted Images (DWI) were acquired on a 3T MRI scanner using a free-breathing, spin echo-based echo-planar imaging (SE-EPI) sequence with six b-values (0, 30, 60, 100, 600, 1000 s/mm2). Tumors were segmented using Dynamic Contrast Enhanced (DCE) MRI and registered to the DWI images. A voxel-wise, bi-exponential, IVIM model was fitted to the DWI images to derive the perfusion fraction (f), diffusion coefficient (D), and pseudo-diffusion coefficient (D*) distributions inside the tumor. IVIM parameter distributions were described using histogram analysis by extracting the median, standard deviation, skew, kurtosis, and percentiles (5, 10, 25, 75, 90, 95). Statistical comparisons between pre- and post-RT images were performed using the nonparametric permutation test for small sample sizes. Kaplan-Meier analysis of pre- and post-RT showed significantly reduced survival (p = 0.04) in patients who had a CA19-9 increase (n = 6) compared to those who decreased or stayed the same (n = 6). The median f showed a significant increase (p = 0.03) in patients who experienced a decrease in CA19-9 while D showed a significant decrease (p = 0.03). Among the calculated histogram percentiles, both the 5th and 10th percentile in the f distribution showed a near-significant increase (p = 0.06) when CA19-9 decreased while the 95th of the D distribution showed a near-significant decrease (p = 0.06). In patients who experienced an increase in CA19-9, a near-significant change (p = 0.06) in the skew (decrease) and kurtosis (increase) of the f distribution was observed. D* showed no significant correlations across all testing. Both f and D exhibited significant changes in PDAC patients undergoing RT and chemotherapy, reflecting changes in tumor response to treatment. The findings warrant further investigation to utilize IVIM in characterizing treatment response in PDAC patients.