Gastrointestinal Motility-Induced Interplay in Pancreas Proton Therapy: Motion Simulation and Dosimetric Impact

Area of Science:

• Medical Physics
• Radiation Oncology
• Biomedical Engineering

Background:

• Gastrointestinal (GI) motility introduces motion uncertainties in pancreas pencil-beam scanning (PBS) proton therapy.
• Understanding the dosimetric impact of GI motion is crucial for accurate treatment planning.

Purpose of the Study:

• To simulate GI motility and quantify its dosimetric interplay effects in pancreas PBS.
• To assess the influence of fractionation and motion amplitude on target coverage and organ-at-risk (OAR) doses.

Main Methods:

• Developed a physiology-informed GI motion simulator for time-resolved motion modes (peristalsis, segmentation, HAPC).
• Integrated the simulator with a 4D dose accumulation tool for PBS delivery analysis.
• Studied seven pancreatic cancer patients, comparing MODERATE and MAX motion settings, and single-fraction vs. full-treatment deliveries.

Main Results:

• GI motility caused measurable interplay effects, degrading CTV D95% and increasing OAR doses.
• MAX motion resulted in larger dose differences and wider dose ranges compared to MODERATE motion.
• Conventional fractionation significantly reduced interplay effects, while hypofractionation offered only partial mitigation.

Conclusions:

• GI motility is a significant, geometry-dependent source of interplay in pancreas PBS.
• This study presents the first plan-specific replay of clinical PBS deliveries on motility-only anatomies.
• Fractionation is an effective strategy to mitigate GI motility-induced interplay effects in pancreas PBS.