KEY POINTS
- This simulation study used clinical pencil-beam scanning proton plans from seven patients with pancreatic adenocarcinoma. Six received conventionally fractionated treatment (45–59.4 Gy in 25–33 fractions), while one received 30 Gy in 5 fractions.
- A physiology-informed model simulated peristalsis, rhythmic segmentation, and high-amplitude propagated contractions in the stomach, duodenum, and small bowel. Dynamic spot delivery was replayed using Monte Carlo dose calculation under moderate and maximum motion conditions.
- With maximum motion during one fraction, mean clinical target volume D95% changed by −1.34%, ranging from −5.52% to +0.08% relative to the static plan. The mean target-dose range across motion scenarios was 5.38%, reaching 12.94% in one patient.
- Maximum single-fraction motion produced organ-at-risk D2% ranges of 6.90% for the duodenum, 8.47% for the stomach, and 6.74% for the small bowel; the maximum individual small-bowel range reached 25.57%. Mean dose changes were smaller, indicating that upper-tail excursions rather than averages carried the largest effect.
- Full-course accumulation narrowed target and organ-at-risk dose ranges, particularly with 25–33 fractions, whereas the 5-fraction simulation showed only partial averaging. Respiration, daily gas or filling changes, patient-specific motility, physical delivery measurements, toxicity, and clinical outcomes were not evaluated.
CLINICAL TAKEAWAY
Gastrointestinal motility may be relevant when a proton beam’s distal fall-off lies close to mobile stomach or bowel, particularly in hypofractionated pancreatic treatments. The findings support attention to beam geometry and distributional organ-at-risk dose excursions, but this small simulation study is technically relevant rather than practice-changing.
SOURCE
International Journal of Radiation Oncology, Biology, Physics