Initial clinical experience with a radiation oncology dedicated open 1.0T MR-simulation

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• Magnetic Resonance Simulation (MR-SIM) offers potential advantages for radiotherapy treatment planning.
• Comprehensive characterization and quality assurance (QA) are essential for clinical implementation of MR-SIM.

Purpose of the Study:

• To describe the experience with 1.0T MR-SIM, including its characterization, QA program, and features crucial for treatment planning.
• To evaluate the accuracy, image quality, and clinical applicability of MR-SIM, particularly for 4D MRI and ultrashort echo time Dixon (UTE/Dixon) imaging.

Main Methods:

• Developed staffing, safety, and patient screening protocols.
• Utilized an external laser positioning system (ELPS) and MR-compatible couchtop.
• Performed spatial and volumetric analyses comparing CT-SIM and MR-SIM using a stereotactic QA phantom.
• Assessed magnetic field inhomogeneity, 2D and 3D geometric distortion, and ELPS impact on image quality.
• Evaluated combined UTE/Dixon sequences and implemented amplitude-triggered 4D MRI using a motion phantom and a patient.

Main Results:

• MR-SIM demonstrated high volumetric accuracy (<2% difference) and spatial precision (<0.2 mm landmark distance) compared to CT-SIM.
• Magnetic field inhomogeneity was minimal (<2 ppm), and geometric distortion was within acceptable limits, though increasing with distance from isocenter.
• UTE/Dixon sequences enabled bone and air detectability, while 4D MRI achieved acceptable image quality in approximately 7 minutes for patient scans.

Conclusions:

• The 1.0T MR-SIM system was successfully integrated into the clinical workflow with robust QA procedures.
• The study confirmed the clinical applicability of 4D MRI and UTE imaging for single-modality treatment planning using MR-SIM.
• Further characterization of geometric distortion at greater distances from isocenter is recommended.