MRI geometric distortion: Impact on tangential whole-breast IMRT

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• Accurate target delineation is crucial for effective radiotherapy.
• Magnetic resonance imaging (MRI) offers superior soft-tissue contrast for treatment planning.
• Geometric distortions in MRI can potentially compromise treatment accuracy.

Purpose of the Study:

• To evaluate the impact of MRI geometric distortions on whole-breast intensity-modulated radiotherapy (IMRT) planning.
• To assess the influence of residual system and patient-induced distortions on treatment dosimetry.
• To determine the clinical acceptability of MRI-based radiotherapy plans.

Main Methods:

• Retrospective analysis of 18 patients undergoing whole-breast radiotherapy with both CT and MRI data.
• Imaging distortion phantoms on 3T and 1T MRI systems to quantify residual system distortions.
• Simulating MRI-based planning by applying distortion maps to CT datasets.
• Generating and evaluating IMRT plans based on distorted and original CT data.

Main Results:

• Maximum residual systematic distortions measured were 7.9 mm (3T) and 11.9 mm (1T).
• Residual system distortions alone did not lead to clinically unacceptable plans.
• Combined MRI systematic and patient-induced distortions resulted in unacceptable dosimetry for 8 plans.

Conclusions:

• Residual MRI system distortions alone have a minimal impact on whole-breast IMRT dosimetry.
• The combination of MRI systematic and patient-related distortions can compromise treatment plan quality.
• Careful consideration of MRI distortions is necessary for MRI-only radiotherapy planning.