Quantification of esophageal tumor motion on cine-magnetic resonance imaging

Purpose To quantify the movement of esophageal tumors noninvasively on cine-magnetic resonance imaging (MRI) by use of a semiautomatic method to visualize tumor movement directly throughout multiple breathing cycles. Methods and Materials Thirty-six patients with esophageal tumors underwent MRI. Tumors were located in the upper (8), middle (7), and lower (21) esophagus. Cine-MR images were collected in the coronal and sagittal plane during 60 seconds at a rate of 2 Hz. An adaptive correlation filter was used to automatically track a previously marked reference point. Tumor movement was measured in the craniocaudal (CC), left-right (LR), and anteroposterior (AP) directions and its relationship along the longitudinal axis of the esophagus was investigated. Results Tumor registration within the individual images was typically done at a millisecond time scale. The mean (SD) peak-to-peak displacements in the CC, AP, and LR directions were 13.3 (5.2) mm, 4.9 (2.5) mm, and 2.7 (1.2) mm, respectively. The bandwidth to cover 95% of excursions from the mean position (c95) was also calculated to exclude outliers caused by sporadic movements. The mean (SD) c95 values were 10.1 (3.8) mm, 3.7 (1.9) mm, and 2.0 (0.9) mm in the CC, AP, and LR dimensions. The end-exhale phase provided a stable position in the respiratory cycle, compared with more variety in the end-inhale phase. Furthermore, lower tumors showed more movement than did higher tumors in the CC and AP directions. Conclusions Intrafraction tumor movement was highly variable between patients. Tumor position proved the most stable during the respiratory cycle in the end-exhale phase. A better understanding of tumor motion makes it possible to individualize radiation delivery strategies accordingly. Cine-MRI is a successful noninvasive modality to analyze motion for this purpose in the future.