Modeling intra-fractional abdominal configuration changes using breathing motion-corrected radial MRI

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• Abdominal organ motion introduces geometric uncertainties in gastrointestinal radiotherapy.
• Investigating slow, drifting organ motion is essential for improving treatment accuracy.

Purpose of the Study:

• To investigate slow drifting motion of gastrointestinal organs.
• To quantify geometric uncertainties introduced by this motion.
• To develop patient-specific motion models for radiotherapy planning.

Main Methods:

• Utilized 3D radial MRI sequences (20-min scan length) to capture slow organ motion.
• Applied multi-temporal resolution image reconstruction to remove breathing and cyclic GI motion.
• Employed B-spline deformable registration and principal component analysis (PCA) for motion analysis and modeling.

Main Results:

• Averaged motion velocities for small bowel, colon, duodenum, and stomach ranged from 0.6 to 2.0 mm/min.
• Average Hausdorff distances for organs at risk (OARs) ranged from 4.6 to 5.6 mm.
• A margin >4.5 mm was needed for >55% OAR occupancy probability; margin estimates were stable across time windows.

Conclusions:

• Slow drifting motion of GI organs is significant and impacts radiotherapy geometric uncertainties.
• These uncertainties must be accounted for in radiotherapy planning and delivery.
• Patient-specific motion models can aid in managing these uncertainties.