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Assessment of the Respiratory Motion Induced Inter-Sessional Liver Positional Variation Using Four-Dimensional MR

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Y Zhou

Y Zhou*, OL Wong , J Yuan , KY Cheung , SK Yu , Hong Kong Sanatorium & Hospital, Happy Valley, Hong Kong


MO-RAM-GePD-J(B)-4 (Monday, July 31, 2017) 9:30 AM - 10:00 AM Room: Joint Imaging-Therapy ePoster Lounge - B

Purpose: Respiratory motion compromises the outcome of abdomen radiotherapy. Owing to its superior soft-tissue contrast and non-ionizing radiation, 4-dimensional(4D) MR has been developed to characterize patient-specific respiratory motion for radiotherapy. The purpose of this study was to assess respiration induced liver positional variation and how such variation changed between sessions using 4D-MR.

Methods: Three healthy volunteers were recruited and each received 5 scans. Subjects were immobilized using a customized vacuum-bag in the supine position with arms up. Coronal MR images were acquired with a 1.5T MR-simulator under free breathing (HASTE, TR/TE=300/43ms, FOV=480x480mm, voxel size=2.5x2.5x4mm³, acquisition time=3.75sec, temporal resolution=3.3 fps). The respiratory profile was recorded using an external surrogate. 4D-MR data was retrospectively sorted into 10 respiratory phase bins. The region of interest(ROI) was set to the hepatic vessel. The range of the respiratory motion was defined as the displacement of the ROI centroid between end-exhalation and end-inhalation and was assessed in the left–right(LR) and superior–inferior(SI) directions. The inter-fractional positional variation was defined as the ROI positional difference with respect to the first session. Wilcoxon rank-sum test was used to compare the inter-fractional positional variations at end-inhalation with those at end-exhalation for each direction.

Results: The group means of respiratory motion were 0.27±1.11mm (range, -2.50–2.50mm) and 7.13±1.97mm (range, 0.00–22.50mm) in LR and SI directions, respectively. The group means of inter-fractional positional variation at all phases were 2.61±0.58mm (mean±SD) and 4.43±1.41mm in the LR and SI direction, respectively. The end-exhalation phase has the smallest inter-fraction positional variation in SI direction(-1.54±3.77mm). The inter-fractional positional variation at end-inhalation and end-exhalation in the LR and SI directions were not significantly different (LR:p=0.64, SI:p=0.45).

Conclusion: Our study indicated that the inter-fractional positional variation of the hepatic vessel under free breathing condition was smaller at end-exhalation than at end-inhalation, but the difference was not significant.

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