Fasting Alone Does Not Stabilize Stomach Volume During Pancreatic SBRT Journal: Practical Radiation Oncology | June 2026

• Pancreatic stereotactic body radiotherapy (SBRT) requires highly precise treatment because the pancreas lies immediately adjacent to radiosensitive organs such as the stomach and duodenum.
• Most centers instruct patients to fast before simulation and treatment, assuming that an empty stomach will reduce daily variation and improve treatment reproducibility.
• This study evaluated whether a standardized 2-hour fasting protocol actually produces consistent stomach volumes during pancreatic SBRT.
• Seventy-four patients undergoing pancreatic SBRT were analyzed with repeated imaging throughout treatment.
• The results showed that fasting instructions alone were insufficient for many patients.
• Approximately 58% of patients demonstrated substantial day-to-day stomach volume variability despite following identical fasting instructions.
• Patients with larger stomach volumes at simulation were more likely to show significant variation during treatment.
• A baseline stomach volume of approximately >200 cc identified patients at higher risk for inter-fraction variability.
• Surprisingly, total stomach volume correlated poorly with the volume of stomach located near the treatment target.
• This finding is clinically important because radiation toxicity depends primarily on the stomach immediately adjacent to the planning target volume rather than the total gastric volume. • Simply measuring overall stomach size may therefore be inadequate when assessing radiation risk.
• The study challenges the common assumption that uniform fasting instructions guarantee reproducible anatomy during pancreatic radiation therapy.
• Adaptive radiotherapy, image guidance, and individualized preparation strategies may remain necessary despite fasting protocols.
• Baseline simulation imaging may help identify patients who require more intensive motion management or adaptive planning.
• The findings are particularly relevant as pancreatic SBRT continues to expand and dose escalation strategies increasingly rely on precise organ-at-risk avoidance.

Bottom line: A standard 2-hour fasting protocol does not reliably produce consistent stomach volumes during pancreatic SBRT. Patients with larger baseline stomach volumes are particularly prone to day-to-day variability, highlighting the need for individualized image-guided and adaptive treatment strategies.