Evaluation of Intrafractional Anatomical Variations During Liver Magnetic Resonance-guided Adaptive Radiation Therapy...

Area of Science:

• Medical Physics
• Radiation Oncology
• Medical Imaging

Background:

• Liver magnetic resonance-guided adaptive radiation therapy (MRgART) requires precise tumor targeting.
• Intrafractional anatomical variations can impact treatment accuracy.
• Abdominal compression (AC) is used to reduce respiratory motion during liver treatments.

Purpose of the Study:

• To quantify intrafractional anatomical variations during liver MRgART under AC.
• To investigate the utility of optical flow calculations for assessing tumor motion.
• To analyze motion patterns based on tumor location within the liver.

Main Methods:

• Analysis of 387,566 slices from 145 cine MRI series in 27 patients undergoing liver MRgART with AC.
• Application of Farnebäck optical flow calculations to determine superior-inferior (SI) motion and root-mean-square error (RMSE).
• Classification of motion parameters (SI, RMSE) in coronal and sagittal planes by tumor location (Couinaud segments).

Main Results:

• Median SI motion ranges were 6.1 mm (coronal) and 8.1 mm (sagittal).
• Segments VI + VII exhibited the largest motion ranges (SI_coronal: 6.5 mm, SI_sagittal: 10.6 mm) and RMSE values.
• Dorsally located tumors showed significant sliding motion, contributing to observed differences.

Conclusions:

• Optical flow analysis underestimated SI motion in the coronal plane compared to the sagittal plane.
• Monitoring tumor motion in the sagittal plane is crucial due to liver sliding.
• Individualized treatment margins based on tumor location are recommended for liver MRgART.