Surrogate-driven deformable motion model for organ motion tracking in particle radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-guided Therapy

Background:

• Particle radiation therapy requires precise tumor targeting, which is challenged by respiratory motion.
• Current methods often use rigid alignment, limiting accuracy for dynamic treatments.

Purpose of the Study:

• To develop and test a novel tumor tracking method for particle radiation therapy.
• To provide daily respiratory dynamics using a motion model and external surrogate.
• To enable dynamic localization of anatomical structures for improved treatment adaptation.

Main Methods:

• A patient-specific breathing motion model was created using deformable image registration on 4D CT scans.
• The model was adapted for baseline anatomical variations.
• Intrafractional amplitude and phase parameters were derived from external surface displacement signals.

Main Results:

• The method achieved geometric accuracy of 0.6–1.7 mm for lung lesion localization across breathing phases.
• Tracking errors for organs at risk averaged below 1.3 mm.
• Median absolute variation in water equivalent path length (WEL) was within 1.9 mm-WEL for simulated particle beams.

Conclusions:

• The developed tumor tracking method shows feasibility for particle radiation therapy.
• It offers significant improvement over rigid alignment by enabling dynamic localization and WEL variation assessment.
• This approach supports particle beam range adaptation for more effective cancer treatment.