Full Abdominal Motion Interplay In Pencil Beam Scanning Proton Therapy: Integrating Respiratory and Gastrointestinal Dynamics
Abstract
Purpose
To implement a full abdominal motion model that combines respiration with gastrointestinal (GI) motility and quantify its interplay impact in pencil-beam scanning (PBS) proton therapy.
Methods
We compared full-motion (GI motility with respiratory superposition) against GI motility-only simulations in six abdominal cases (three pancreas and three liver). Respiratory deformation vector fields (DVFs) were derived from 4DCT via deformable registration. GI motility (peristalsis, rhythmic segmentation, and high-amplitude propagated contractions) was generated along stomach/duodenum/small-bowel centerlines using traveling/standing waveforms, with local radius modulations mapped to 3D DVFs via boundary-aware kernels. For full-motion modeling, the respiratory DVF and GI-DVF were composed at spot time to perform realistic 4D dose replay. Endpoints were interplay-induced deviance (Δ) vs static for clinical-target-volume (CTV) D95% and organ-at-risk (OAR) D2%, and distribution width (the width of CTV-D95% or OAR-D2% between two extreme scenarios). Both are reported as mean [min, max] (Gy) for single fraction (1-fx) and full course (30-fx) replay.
Results
Full-motion modeling produced larger interplay-induced dosimetric deviations and wider dose distributions than GI-only. For CTV D95% (1-fx), dose deviations Δ was −3.3 [−5.2, 0] Gy with full motion vs −1.4 [−4.4, 0.1] Gy for GI-only. The distribution width was likewise greater for full motion: 4.3 [0.3, 9.9] Gy vs GI-only: 1.8 [0.1, 7.0] Gy. The same results of larger mean shifts and wider spreads in full-motion were also observed across OAR D2% metrics in both pancreas and liver cases. Multiple fractions (full-fx) tightened deviations and narrowed widths in both models but did not fully restore static-like distributions.
Conclusion
A delivery-accurate, respiratory-plus-GI model shows that full abdominal motion produces stronger interplay than GI-only in abdominal PBS. These results support incorporating combined respiratory and GI dynamics in motion-robust planning and evaluation, and using distribution-aware endpoints (Δ and width) when assessing interplay risk.