Abstract: Objective: To explore the dose distribution characteristics between RapidArc and five-field intensity modulated radiotherapy(5F-IMRT) plans in the treatment of locally advanced pancreatic carcinoma,and to provide reference for selecting the appropriate radiation technique in clinic. Methods: Ten patients with locally advanced pancreatic carcinoma were selected.The patients were scanned by simulation CT, and the targets and organs at risk were contoured. RapidArc plan and 5F-IMRT plan were designed respectively. The treatment time and the differences of dose distribution in the targets and organs at risk of RapidArc and 5F-IMRT plans were compared. Results: The conformal index (CI) of RapidArc plan was superior than that of 5F-IMRT plan(P=0.01).The homogeneity index (HI) of targets were similar between two plans (P>0.05). RapidArc plan decreased the maximum dose (D_max) of the spinal cord(P=0.005); RapidArc plan decreased the mean dose(D_mean) of stomach(P=0.019); 5F-IMRT plan decreased the V20 of kidney(P=0.043);RapidArc plan decreased the mean dose(D_mean) of small intestine(P=0.011).The small intestine V10 and V20 of RapidArc plan were lower than those of 5F-IMRT plan(P=0.015,P=0.14); the monitor unit (MU) of RapidArc plan was significantly lower than that of 5F-IMRT plan,with a 18% reduction from the MU level of the latter one,and the treatment time was reduced by 70.3%. RapidArc plan had the smaller doses at liver and kidney compared with 5F-IMRT plan. Conclusion: For the patients with locally advanced pancreatic carcinoma,RapidArc plan has higher CI. RapidArc plan shows the advantages in the protection of organs. Compared with 5F-IMRT,RapidArc plan has less treatment time and significantly improves the curative efficiency.In clinic, the RapidArc plan is recommended.

Key words: pancreatic neoplasms, RapidArc, five-field intensity modulated radiotherapy, conformal index