Potential utility of cone‐beam CT‐guided adaptive radiotherapy under end‐exhalation breath‐hold conditions for pancreatic cancer

PURPOSE: The purpose of this study was to demonstrate the potential utility of cone‐beam computed tomography (CBCT)‐guided online adaptive radiotherapy (ART) under end‐exhalation breath‐hold (EE‐BH) conditions for pancreatic cancer (PC). METHODS: Eleven PC patients who underwent 15‐fraction volumetric‐modulated arc therapy under EE‐BH conditions were included. Planning CT images and daily 165 CBCT images were imported into a dedicated treatment planning system. The prescription dose was set to 48 Gy in 15 fractions. The reference plan was automatically generated along with predefined clinical goals. After segmentation was completed on CBCT images, two different plans were generated: One was an adapted (ADP) plan in which re‐optimization was performed on the anatomy of the day, and the other was a scheduled (SCH) plan, which was the same as the reference plan. The dose distributions calculated using the synthetic CT created from both planning CT and CBCT were compared between the two plans. Independent calculation‐based quality assurance was also performed for the ADP plans, with a gamma passing rate of 3%/3 mm. RESULTS: All clinical goals were successfully achieved during the reference plan generation. Of the 165 sessions, gross tumor volume D (98%) and clinical target volume D (98%) were higher in 100 (60.1%) and 122 (74.0%) ADP fractions. In each fraction, the V (3 Gy) < 1 cm(3) of the stomach and duodenum was violated in 47 (28.5%) and 48 (29.1%), respectively, of the SCH fractions, whereas no violations were observed in the ADP fractions. There were statistically significant differences in the dose–volume indices between the SCH and ADP fractions (p < 0.05). The gamma passing rates were above 95% in all ADP fractions. CONCLUSIONS: The CBCT‐guided online ART under EE‐BH conditions successfully reduced the dose to the stomach and duodenum while maintaining target coverage.