Intrafractional motion models based on principal components in Magnetic Resonance guided prostate radiotherapy

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image-Guided Therapy

Background:

• MR-Linac systems enable high-resolution imaging during radiotherapy.
• This facilitates the creation of individualized motion models for treatment fractions.
• Intrafractional motion modeling is crucial for precise dose delivery.

Purpose of the Study:

• To investigate the feasibility of a principal component analysis (PCA)-based intrafractional motion model for the male pelvic region.
• To assess the accuracy and components of such a model.

Main Methods:

• Utilized 4D-scans of nine healthy male volunteers covering the pelvic region.
• Performed deformable image registration with an optical flow algorithm.
• Applied PCA to displacement vector fields to construct and evaluate individual motion models.

Main Results:

• Accurate registration achieved with DICE overlap generally $$ 0.95.
• The first principal component explained 50% or more of the motion for all subjects.
• The model explained motion down to approximately 1 mm using 1-2 components, with subject-specific component variations.

Conclusions:

• An individualized intrafractional male pelvic motion model is feasible.
• The developed model demonstrated geometric accuracy of about 1 mm.
• PCA-based motion modeling shows promise for enhancing radiotherapy precision.