Do Uniform Fasting Instructions Lead to Reproducible Stomach Volumes in Patients Being Treated With Radiation to the Pancreas?

Abstract

This retrospective study determines if uniform fasting protocols successfully limit stomach volume variation and proximity to the planning target volume throughout radiation treatment. A total of 74 patients with cancer were instructed to fast for 2 hours before receiving stereotactic body radiation therapy to their pancreas. The entire stomach and the stomach near the planning target volume (stomach_3cm) were contoured at simulation and on each treatment image. Patients were grouped into 3 clusters based on their SD in stomach volume across treatments. The simulation stomach volume was used as a predictor of successful fasting using the Mann-Whitney U test. The relationship between the stomach volume and the stomach_3cm volume was calculated. Among 74 patients, 58% were classified as unsuccessful at fasting with a significantly larger SD than the successful cluster (P < .00001). The volume at simulation of the successful fasting cluster (183 cm³) was significantly different from the variable and unsuccessful clusters (255 cm³ and 238 cm³) (P < .001). The correlation coefficient of the stomach and stomach_3cm was 0.28 (R² = 0.08). Uniform fasting instructions did not result in reproducible stomach volumes during treatment for the majority of patients. Patients with a simulated stomach volume ≥200 cm³ are likely to demonstrate greater interfraction variability. The entire stomach volume during treatment did not correlate well with the stomach volume near the tumor. These findings suggest that under standardized fasting protocols, baseline stomach volume may help identify patients at a higher risk of gastric variability, and that additional strategies may be needed to improve reproducibility in selected patients.