Dosimetric effect of the intestinal gas of online adaptive stereotactic body radiotherapy on target and critical organs without online electron density correction for pancreatic cancer.

Objective: This study aimed to assess the dosimetric effect of intestinal gas of stereotactic magnetic resonance (MR)-guided adaptive radiation therapy (SMART) on target and critical organs for pancreatic cancer without online electron density correction (EDC).
Methods: Thirty pancreatic cancer patients who underwent online SMART were selected for this study. The treatment time of each stage and the total treatment time were recorded and analyzed. The concerned dose-volume parameters of target and organs-at-risk (OAR) were compared with and without an intestinal gas EDC using the Wilcoxon-signed rank test. Analysis items with p value < 0.05 were considered statistically significant. The relationships between dosimetric differences and intestinal gas volume variations were investigated using the Spearman test.
Results: The average treatment time was 82 min, and the average EDC time was 8 min, which accounted for 10% of the overall treatment time. There were no significant differences in CTV (GTV), PTV, bowel, stomach, duodenum, and skin ( p > 0.05) with respect to dose volume parameters. For the D _max of gastrointestinal organs ( p = 0.03), the mean dose of the liver ( p = 0.002) and kidneys ( p = 0.03 and p = 0.04 for the left and right kidneys, respectively), there may be a risk of slight overestimation compared with EDC, and for the D _max of the spinal cord ( p = 0.02), there may be a risk of slight underestimation compared with EDC. A weak correlation for D ₉₅ in the PTV and D _{0.5 cc} in the duodenum was observed.
Conclusion: For patients with similar inter-fractional intestinal gas distribution, EDC had little dosimetric effects on the D _{0.5 cc} of all GI organs and dose volume parameters of target in most plans.
Advances in Knowledge: By omitting the EDC of intestinal gas, the online SMART treatment time can be shortened.