Online image guided tumour tracking with scanned proton beams: a comprehensive simulation study

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Therapy

Background:

• Accurate 3D tumour motion and density information are vital for scanned particle beam therapy.
• Previous work established a model-based method for predicting deformable motions from sparse surrogate data.

Purpose of the Study:

• To investigate the effectiveness of tumour tracking for scanned proton beam therapy.
• To evaluate the impact of 're-tracking' on reducing residual motion uncertainties.
• To compare 2D, 2D deformable, and 3D beam tracking strategies.

Main Methods:

• Simulated 4DCTs derived from 4DMRI datasets were used for three liver motion cases (10-20 mm).
• Inter-breath-cycle motion variability was incorporated into simulations.
• Three beam tracking strategies (2D, 2D deformable, 3D) and three-times re-tracking were applied.

Main Results:

• Without tracking, significant interplay effects were observed (CTV D5-95: 34.9-79.4%).
• Tracking reduced interplay effects (D5-95: 15.1-29.1%), with 3D tracking showing slight advantages.
• Three-times re-tracking further reduced D5-95 (to 13.0-13.8% for 20 mm motion) and mitigated 'hot spots' from inverse interplay effects.

Conclusions:

• For motions >10 mm, tracking alone is insufficient and can increase normal tissue dose.
• Three-times re-tracking substantially enhances all tracking methods.
• 3D re-tracking offers advantages over 2D re-tracking only in the largest motion scenarios.