Abstract:

Abstract:Objective To compare the dosimetric parameters of volumetric modulated arc therapy（VMAT）,fixed field intensity modulated radiation therapy（IMRT） and three-dimensional conformal radiotherapy（3D-CRT）in the radiotherapy for the patients with locally recurrent nasopharyngeal carcinoma,and to analyze their characteristics.Methods Twelve  patients with locally recurrent nasopharyngeal carcinoma  were treated with VMAT,IMRT and 3D-CRT plan designed by Pinnacle 9.2 and Preciseplan 2.03 treatment planning system.The dosimetric parameters of targeted volumes and organs at risk were compared between three groups.Results The conformation indexes(CI) of VMAT and IMRT plans were similar,and they were both better than 3D-CRT plan,the difference  was significant（P<0.05）.The homogeneity index(HI) in three groups were similar,there were no statistically significant differences between them(P>0.05).The monitor units(MU) and beam time in 3D-CRT group were bettethose in other two groups,and VMRT group was better than IMRT group,the statistical differences were observed between three groups（P<0.05）.There were no statistical differences of organs at risk such as brainstem and lens between three groups（P>0.05）.The doses of the spinal cord,optic nerve,optic chiasm and temporal lobe of brain in VMAT and IMRT groups were better than those in 3D-CRT group,there were statistical differences between them（P<0.05）,and the data in VMAT and IMRT groups were similar,and there were no statistical differences（P>0.05）.Conclusion There are differences of the targeted dose distribution between the three kinds of radiation technology,while VMAT and IMRT plans  can cover the targeted areas and reduce the received doses of organs at risk.The CI,MU and beam time of VMAT plan are better than those of IMRT plan.3D-CRT plan only has advantage in the MU and beam time.

Key words: nasopharyngeal neoplasms, tumor recurrence, dosimetric parameter, volumetric modulated arc radiotherapy, intensity modulated radiotherapy, 3-dimension