WE-G-BRD-02: Dynamic Contrast Enhanced (DCE) MRI for Response Assessment of Inoperable Lung Tumors for Patients Undergoing SBRT Treatment

Authors


Abstract

Purpose:

To investigate the changes in T1 perfusion coefficients derived from analysis of Dynamic contrast enhanced (DCE) MRI of lung cancer patients undergoing SBRT.

Methods:

3D DCE-MRI scans utilizing fast-field echo sequences were used in this prospective IRB-approved study of lung cancer patients undergoing SBRT during simulation, 1h after first fraction (8 Gy), after 5 fractions (40 Gy) and 4 weeks after treatment. The scan acquisition parameters were TR/TE = 3.6/1.6 ms, flip angle= 12°, voxel size = 2.7×2.7×5 mm3, 3.2 sec temporal resolution with 60 dynamics. The modified Toft's model was used to perform a voxel-by-voxel fit of the perfusion coefficients Ktrans and Kep using the Levenberg-Marquardt algorithm. Initial area under the time-concentration curve (IAUC) was evaluated at 30, 60, 90 and 180 seconds. The GTV was drawn on each coronal volume after deformable registration to the pre-treatment anatomical MRI. Changes in Ktrans, Kep and IAUC's were evaluated to assess tumor response to SBRT.

Results:

All time points of the first patient were analyzed. The median Ktrans values of the tumor ROI were 0.76, 0.53, 0.89, 0.28 min−1 at pre-treatment, after 8 Gy, immediately and 4 weeks post-treatment. The median Kep values were 1.47, 1.27, 1.01, and 0.90 min−1 respectively. Both Ktrans and Kep histogram distributions shifted towards lower values 4 weeks post-treatment. After normalizing IAUC values to tumor volumes, median IAUC30 values were 0.032, 0.022, 0.05 and 0.026 mol.s/L and median IAUC180 values were 0.25, 0.26, 0.43 and 0.52 mol.s/L respectively.

Conclusion:

Decreased Ktrans values from pre-treatment to 4 weeks post-treatment signifies decreased microvessel density and permeability. The decreased Kep values indicate a shallower slope in the delayed phase of the kinetic curve. Both distribution shifts towards lower values signify reduced contrast perfusion, implying reduced tumor perfusion. Both quantities are indicative of tumor response to SBRT treatment.

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