Predicting the daily gastrointestinal doses of stereotactic body radiation therapy for pancreatic cancer based on the shortest distance between the tumor and the gastrointestinal tract using daily computed tomography images

OBJECTIVES: We aimed to investigate whether daily computed tomography (CT) images could predict the daily gastroduodenal, small intestine, and large intestine doses of stereotactic body radiation therapy (SBRT) for pancreatic cancer based on the shortest distance between the gross tumor volume (GTV) and gastrointestinal (GI) tract. METHODS: Twelve patients with pancreatic cancer received SBRT of 40 Gy in five fractions. We recalculated the reference clinical SBRT plan (PLAN(ref)) using daily CT images and calculated the shortest distance from the GTV to each GI tract. The maximum dose delivered to 0.5 cc (D(0.5cc)) was evaluated for each planning at-risk volume of the GI tract. Spearman’s correlation test was used to determine the association between the daily change in the shortest distance (Δshortest distance) and the ratio of ΔD(0.5cc) dose to D(0.5cc) dose in PLAN(ref) (ΔD(0.5cc)/PLAN(ref)) for quantitative analysis. RESULTS: The median shortest distance in PLAN(ref) was 0 mm in the gastroduodenum (interquartile range, 0–2.7), 16.7 mm in the small intestine (10.0–23.7), and 16.7 mm in the large intestine (8.3–28.1 mm). The D(0.5cc) of PLAN(ref) in the gastroduodenum was >30 Gy in all patients, with 10 (83.3%) having the highest dose. A significant association was found between the Δshortest distance and ΔD(0.5cc)/ PLAN(ref) in the small or large intestine (p < 0.001) but not in the gastroduodenum (p = 0.404). CONCLUSIONS: The gastroduodenum had a higher D(0.5cc) and predicting the daily dose was difficult. Daily dose calculations of the GI tract are recommended for safe SBRT. ADVANCES IN KNOWLEDGE: This study aimed to predict the daily doses in SBRT for pancreatic cancer from the shortest distance between the GTV and the gastrointestinal tract. Daily changes in the shortest distance can predict the daily dose to the small or large intestines, but not to the gastroduodenum.