Complex Abdominal Organ Motion Assessed From Magnetic Resonance Imaging International Journal of Radiation Oncology, Biology, Physics POSTER VIEWING ABSTRACT| VOLUME 96, ISSUE 2, SUPPLEMENT , E696-E697, OCTOBER 01, 2016
Date
10/01/2016Abstract
Purpose/Objective(s)
Organ motion in the abdomen is complex due to the interplay of respiratory and bowel motion. An understanding of this complex motion is the first step in developing effective motion management strategies. 4DCT measures mostly respiratory motion and cannot fully evaluate the complex motions over time. We measure these motions by analyzing 2D (cine) and 3D MRI compared to 4DCT data acquired from pancreatic and liver cancer patients.
Materials/Methods
Motion for relevant organs, including pancreas, duodenum, stomach, bowels, liver, and kidneys, was measured within 2-45 mins, possible time durations for MRI simulation and image guided delivery. Motion was evaluated based on 2D (cine) and 3D MRI data from 10 randomly selected patients acquired while in their treatment immobilization devices. We used motion management strategies during MR simulation to minimize the effects of motion. Specifically, the T2 (∼15 mins prior to contrast injection) and DWI images were respiratory triggered at the end of expiration. The multiphase dynamic contrast enhanced (DCE), pre, and 5 min post contrast injection images were acquired. 4DCT (∼5 seconds) data was also analyzed for comparison. The vertebral body (VB) was also contoured and motion was analyzed to evaluate patient displacement. Organ motion was measured by calculating centroid displacements relative to T2 MRI.
Results
From 4DCT (∼1 breathing cycle) only provided us with respiratory amplitude motion extending up to 2 cm. From 2D MRI we found that additional motion was introduced in some breathing cycles, unrelated to respiratory motion, increasing the motion amplitude up to an additional 1 cm. From 3D MRI we analyzed motion related to physical displacement and other organ motion. We found the left-right (LR) motion of the VB to reach up to 2 cm and 1 cm in the anterior-posterior (AP) direction. Organ motion from T2 MR to precontrast (∼15-20 mins) was: 0.1 - 4 cm in LR, 0.1-2 cm in AP, and 0.1-3 cm in superior-inferior (SI) directions. Organ motion from precontrast to portal venous phase (∼5 mins) was measured up to 2 cm in any direction. Measured motion from portal venous phase to post contrast (∼2.5 mins) was up to 1 cm. The LR motion was the most irregular.
Conclusion
Abdominal organ motion is complex. Despite motion management strategies significant motion can occur. This is due to inconsistencies in the patient performing breath holds, resetting of the navigator gains used for respiratory triggering, and bulk patient motion occurring over the MR sim exam. Motion can be in any direction due to the interplay of respiratory, bowel, and stomach motion. Although patient imaging prior to treatment is done within 5 mins of treatment, additional motion can be present throughout a longer treatment. This large, complex, and variable motion should be managed by techniques such as real-time intrafractional motion tracking.
Author List
E.A. Omari Y. Song J. Christian E.S. Paulson B.A. Erickson A. LiAuthor
Beth A. Erickson MD Professor in the Radiation Oncology department at Medical College of WisconsinView Online
