2075 - Determining the Ideal Uptake Time for Gadoxetate Disodium-Enhanced Liver Tumor Delineation on a 0.35 T MR-Linac

02:30pm - 04:00pm PT

Hall F

Screen: 1

Presenter(s)

Eli Grant, - Department of Radiation Oncology, Lennar Foundation Comprehensive Cancer Center, City of Hope National Medical Center, Irvine, CA, Irvine, CA

E. Grant¹, A. Kassardjian², C. Shi³, H. Ai⁴, A. L. Schwer¹, J. Weng¹, C. J. Ladbury², A. Liu², T. M. Williams², P. Lee¹, and B. Maraghechi¹; ¹Department of Radiation Oncology, Orange County Lennar Foundation Cancer Hospital, Irvine, CA, ²Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, ³City of Hope Orange County, Irvine, CA, ⁴Department of Radiation Oncology, Lennar Foundation Comprehensive Cancer Center, City of Hope National Medical Center, Irvine, CA

Purpose/Objective(s): Accurate tumor delineation is crucial for effective MR-guided radiation therapy (MRgRT) in liver-directed treatments. Gadoxetate disodium is a paramagnetic contrast agent used in MRI liver imaging, and in this study, we explore its effectiveness in tumor delineation with respect to uptake time.

Materials/Methods: The thirteen patients used for this study are undergoing liver-directed MRgRT and are scanned on a 0.35 T MR-Linac before and after contrast injection. Scans were taken at 5-, 10-, 20-, and 30-minute time intervals post-injection. All the pre- and post-contrast images were analyzed by drawing three regions of interest (ROIs) held constant over each scan for a given patient in healthy tissue, lesion, and air. The contrast-to-noise ratio (CNR) was calculated for each scan based on mean pixel intensity and standard deviation within the ROI. The CNR values were then normalized and averaged over all patients’ scans at different times post-contrast to evaluate the effectiveness of Gadoxetate disodium in tumor delineation over time.

Results: CNR values increase over time with a peak value of 0.85 +/- 0.27 observed at 20 minutes post injection. At 30 minutes post-injection, the CNR decreased slightly with an average value of 0.70 +/- 0.32. Lesion enhancement was limited in two of the thirteen patients used in this study.

Conclusion: For most of the patients, Gadoxetate disodium provided effective liver tumor contrast enhancement with a maximum CNR at 20 minutes post-injection. Better visualization of the tumor not only improves target delineation for physician contouring but also increases tracking accuracy of the motion management during treatment. This can enable dose escalation and better normal tissue sparing. Knowing the optimum uptake time after injection also helps improve workflow efficiency by avoiding unnecessarily long patient wait times on the treatment couch.