A hybrid 2D/4D-MRI methodology using simultaneous multislice imaging for radiotherapy guidance

Area of Science:

• Medical physics
• Radiotherapy technology
• Magnetic Resonance Imaging (MRI)

Background:

• Respiratory motion significantly impacts the accuracy of abdominothoracic radiotherapy.
• Effective motion management requires fast tumor imaging for multileaf collimator (MLC) tracking and full field-of-view imaging for 4D dose accumulation.

Purpose of the Study:

• To introduce and evaluate a hybrid 2D/4D-MRI methodology for simultaneous MLC tracking and 4D dose accumulation on a 1.5 T MR-linac.
• To enable precise tumor motion management and accurate dose delivery in radiotherapy.

Main Methods:

• Developed a hybrid 2D/4D-MRI technique using simultaneous multislice (SMS) accelerated MRI sequences.
• Acquired data in healthy volunteers and used an in-silico phantom for validation.
• Performed MLC tracking experiments with real-time SMS data reconstruction and dosimetry experiments using a 4D motion phantom.

Main Results:

• Achieved high correlation (0.996-0.998) for real-time motion estimation with low median errors (0.0-0.2 mm).
• Reduced system latency significantly using a prediction filter.
• Demonstrated accurate GTV coverage (97-101%) and dose agreement with reference delivery.

Conclusions:

• The hybrid 2D/4D-MRI methodology accurately extracts real-time motion for MLC tracking in abdominothoracic radiotherapy.
• The method simultaneously reconstructs 4D-MRIs for precise dose accumulation, improving treatment accuracy.