Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_7_3181 - Initial Feasibility of a Prospective Study Investigating the use of Multiparametric MR Imaging including Intravoxel Incoherent Motion (IVIM) and MR Elastography (MRE) to identify changes after Liver-directed SBRT

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Initial Feasibility of a Prospective Study Investigating the use of Multiparametric MR Imaging including Intravoxel Incoherent Motion (IVIM) and MR Elastography (MRE) to identify changes after Liver-directed SBRT
C. Chipko1, B. Lewis2, E. C. Fields1, A. Vera2, S. Kim2, and T. H. Kim2; 1VCU Massey Cancer Center, Richmond, VA, 2Virginia Commonwealth University, Richmond, VA

Purpose/Objective(s): Rates of liver SBRT are increasing given high rates of local control and low risks of toxicity. However, image registration between CT simulation and diagnostic MRI remains a significant challenge given large variances in breathing motion. Additionally, fibrotic changes versus recurrent or persistent disease is often indistinguishable on post-SBRT images. This study aims to use advanced MRI techniques including intravoxel incoherent motion (IVIM) and MR elastrography (MRE) with an elegant MR-safe motion management system to improve tumor targeting and evaluation of SBRT response.

Materials/Methods: In this prospective pilot study, we are enrolling patients with localized liver tumors amenable to liver-directed SBRT. We obtain Multiparametric (mp) MRI’s with novel techniques including IVIM and MRE, which take into account micro-capillary perfusion and stiffness of tissues, as well as traditional T1 and T2 weighted imaging. Images are performed within 1 month of starting SBRT and again within 3 months of completion. These patients are compared to a cohort undergoing only standard T1 and T2 weighted (T1w and T2w) imaging with standard DWI (ADC). We compare T1w and T2w intensity, and ADC with b-values 0 and 1000 (indicating the degree of diffusion weighting) of the GTV pre- and post-SBRT to those seen with novel mpMRI techniques.

Results: Initial comparisons were made between 2 patients with mpMRIs and 2 patients who underwent conventional T1w, T2w, and DWI MRI’s pre- and post-SBRT. Patients in the mpMRI cohort performed breathing motion control with AV guidance and had less diaphragmatic excursion on image co-registration compared to the conventional group. In both patients undergoing IVIM and MRE, values obtained pre- and post-SBRT were consistent with the directionality of changes seen on standard T2w and ADC, indicating the reliability of these techniques. Within the GTV contour, 50% (2/4) patients had a decrease in mean T2w intensity and mean ADC value while 50% (2/4) patients experienced an increase in mean T2w intensity and ADC values. The two patients with a decrease in post-SBRT values had underlying cirrhosis, while the two patients who had increased post-SBRT values had healthy liver parenchyma. Additionally, MRE values changes were directionally consistent with conventional metrics in cirrhotic and non-cirrhotic patients. Of note, post-SBRT T2w and ADC changes correlate with lower radiation isodose lines (20-30Gy) in 50% of the patients, indicating microstructural changes may occur at lower doses than previously described.

Conclusion: Multiparametric MRI using IVIM and MRE sequences is feasible and consistent with conventional MRI sequences and adds additional information to the level of the micro-capillary and tissue stiffness. With increasing demand for liver-directed therapies, these techniques will allow for the development of MR-based early detection methods for both SBRT response and resistance which appear to differ between cirrhotic and healthy livers.

Author Disclosure: C. Chipko: None. B. Lewis: None. E.C. Fields: None. A. Vera: None. S. Kim: Partnership; Medical Tool and Technology, LLC. President; Korean Medical Physicists in North America. T. Kim: None.

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TU_7_3181 - Initial Feasibility of a Prospective Study Investigating the use of Multiparametric MR Imaging including Intravoxel Incoherent Motion (IVIM) and MR Elastography (MRE) to identify changes after Liver-directed SBRT



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