MRI-guided mid-position liver radiotherapy: Validation of image processing and registration steps

Area of Science:

• Medical Imaging
• Radiation Oncology
• Image Registration

Background:

• Liver SBRT requires precise targeting.
• MRI-guided radiotherapy offers improved soft-tissue visualization.
• A mid-position (midP) workflow can optimize MRI-guided liver SBRT.

Purpose of the Study:

• To propose and validate a novel mid-position (midP) workflow for MRI-guided liver SBRT.
• To assess the generation and registration of midP-MRI and midP-CT images.
• To evaluate different registration methods for daily MRI-guidance.

Main Methods:

• Generated simulation midP-MRI from 4D-MRI using deformable image registration.
• Warped planning midP-CT to midP-MRI anatomy.
• Evaluated three daily MRI-guidance registration methods: 4D rigid, 3D rigid midP-MRI, and 3D deformable midP-MRI.
• Assessed image quality based on acquisition time and registration accuracy using DDM and the full circle method.

Main Results:

• Deformable registration precision for midP-MRI generation was 1.5 mm (median DDM) within the liver.
• MidP-MRI image quality was robust across different acquisition dynamics (5.2% RMS difference).
• Deformable CT-MRI registration error was 1.8 mm (median), and daily MRI-MRI registration was submillimeter.

Conclusions:

• The proposed midP workflow is feasible for MRI-guided liver SBRT.
• High precision was demonstrated across all image processing and registration steps.
• This workflow supports accurate and reliable liver SBRT delivery using MRI guidance.