Room: Exhibit Hall | Forum 5
Purpose: Understanding cardiac motion is critical to accurately assess and even to minimize heart dose during radiation therapy (RT) for thoracic and breast cancers. MRI-guided RT delivery allows acquisition of high resolution MRI, including 2D cine, prior to and during RT delivery, opens the door to manage cardiac motion. In this study, we evaluate cardiac motion based on cine-MRI.
Methods: A total of 13 cine-MRI sets acquired during RT simulation and selected fractions for 6 cancer patients were analyzed. For each patient, the cine-MRIs were acquired with free breathing with durations of 1.0-1.7 minute and ~550 ms acquisition time per slice, in sagittal and coronal planes which crossed near the center of the heart. Heart cross section was contoured in each image frame and its motion was measured in the time sequenced image set.
Results: The inferior border of the heart essentially moved along with diaphragm motion in the superior-inferior directions (10-15 mm across patients). However, the superior sections of the heart move relatively very little. Therefore the maximum superior-inferior centroid motion of the heart slices was found to be only ~2 mm. The anterior and posterior borders of the heart moved 7-15 mm and 5-10 mm respectively, with a maximal centroid motion of 8 mm. The left and right borders of the heart moved 7-10 mm and 5-20 mm respectively with a maximal centroid motion of ~12 mm.
Conclusion: The magnitude of cardiac motion is generally comparable to respiration motion. The cardiac motion in the superior-inferior direction is highly correlated to the breathing motion, especially for the inferior portion of the heart. However, cardiac motion along the sagittal and coronal planes is relatively independent of breathing motion and can be on the order of a centimeter.