Analysis of the Influence Factors of Set-up Errors and Planning
Target Volume in VMAT for Nasopharyngeal Carcinoma
XU Xiaoyan, LI Jinkai, CAO Yuandong, SUN Xinchen
Department of Radiation Oncology, Jiangsu Province Hospital/The First Affiliated Hospital With Nanjing Medical University,
Nanjing Jiangsu 210000, China
Abstract：Objective To analyze the influencing factors of set-up errors in volumetric modulated arc therapy (VMAT) for
nasopharyngeal carcinoma and the range of margin of planning target volume (MPTV). Methods The clinical data of 50 patients with
VMAT nasopharyngeal carcinoma were retrospectively analyzed. All patients were fixed with thermoplastic phantom. Cone beam CT
images were scanned weekly, matched and fused with the planned CT images to obtain the set-up errors in the left and right (x-axis),
head and foot (y-axis), and front and back (z-axis) directions. The theoretical external boundary of the target area was calculated by
using the external boundary formula of the target area. Patients were divided into groups according to body mass index (BMI) and
age (lean group, normal group and overweight group; young group, middle-aged group and elderly group). The differences in set-up
errors and MPTV among different groups were analyzed. Results The overall set-up errors of all patients in the three-dimensional
direction (x-axis, y-axis, z-axis) were (0.198±1.176), (-0.409±1.607) and (-0.140±1.272) mm, respectively, and the theoretical
MPTV of the target area were 2.616, 3.596 and 2.615 mm, respectively. The set-up errors in the x-axis and z-axis of the lean group
were greater than those of the normal group and overweight group (P<0.05), and the theoretical MPTV of x-axis was 3.877 mm.
The set-up errors in the y-axis of the overweight group were greater than those of the lean group and normal group (P<0.05), and the
theoretical MPTV was 3.988 mm. The set-up errors in the x-axis and y-axis of the young group were greater than those of the middleaged
group and the elderly group (P<0.05), and the theoretical MPTV of y-axis was 3.778 mm. In the y-axis direction, age was
weakly negatively correlated with set-up error, while BMI was weakly positively correlated with set-up error (P<0.05). There was no
significant correlation between other indicators. Conclusion During VMAT treatment, although the correlation between age, BMI
and set-up errors is weak, there are still some differences in theoretical MPTV among different groups. It is necessary to optimize the
postural fixation techniques for young, lean and overweight patients to reduce set-up errors. Off line ART technology can be used to
reduce the tumor target area-MPTV.
许晓燕，李金凯，曹远东，孙新臣. 鼻咽癌VMAT摆位误差及靶区外扩
边界影响因素分析[J]. 中国医疗设备, 2023, 38(7): 67-72.
XU Xiaoyan, LI Jinkai, CAO Yuandong, SUN Xinchen. Analysis of the Influence Factors of Set-up Errors and Planning
Target Volume in VMAT for Nasopharyngeal Carcinoma. China Medical Devices, 2023, 38(7): 67-72.
