Interplay-robust optimization for treating irregularly breathing lung patients with pencil beam scanning.

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Biology

Background:

• Pencil beam scanning enables precise tumor targeting but is sensitive to uncertainties.
• Robust optimization (RO) addresses density and setup uncertainties; 4D-RO (4DRO) manages motion but often excludes interplay effects.

Purpose of the Study:

• To evaluate Interplay-Robust Optimization (IPRO) for modeling interplay effects in lung cancer patients.
• To assess IPRO's efficacy with extended motion uncertainties, including breathing amplitude variations.

Main Methods:

• IPRO and a single-cycle variant (IPRO-1C) were tested on lung patient data using synthetic 4D CT (s4DCT) derived from 4D MRI.
• Patient motion scenarios were generated by combining breathing cycles with varying periods and amplitudes.
• IPRO and IPRO-1C were evaluated using 9, 25, and 49 scenarios.

Main Results:

• Both IPRO and IPRO-1C improved near-worst-case CTV D98 target coverage compared to 4DRO.
• IPRO with 49 scenarios achieved the largest OAR dose reductions (average 4.2% improvement).
• IPRO-1C with 9 scenarios offered significant OAR dose reduction (1.7%) with similar computational cost to 4DRO.

Conclusions:

• IPRO provides efficient mitigation of interplay effects, even with single-cycle motion data.
• This approach may reduce the need for real-time motion management, improving treatment efficiency and patient comfort.