新型真空垫在盆腔肿瘤放疗体位固定中的应用评估

A customized vacuum cushion for immobilization in the radiotherapy of pelvic malignancies

目的 对一种新型定制真空垫在盆腔肿瘤放疗体位固定中的应用进行评估，并与传统体位固定方式进行对照研究，以提高盆腔肿瘤摆位精度。方法 66名盆腔肿瘤患者接受放射治疗，将患者按照随机数表法分为3组，每组22名，采用3种不同固定方式：平板固定（N组）、传统真空垫（V组）和定制真空垫（New-V组）。固定效果用三维方向及矢状位轴向旋转的摆位误差测量结果进行评估。结果 New-V组摆位误差在前后（x）、头脚（y）、左右（z）及矢状位轴向旋转角度（r）依次为（0.35±0.37）、（0.21±0.22）、（0.29±0.28） cm和（0.70±0.65）°；N组相应摆位误差依次为（0.44±0.43）、（0.31±0.62）、（0.45±0.60） cm和（1.25±1.00）°；V组依次为（0.38±0.36）、（0.27±0.25）、（0.32±0.29）和（1.09±0.77）°。其中，r值各组比较，差异有统计学意义（F=7.859，P〈0.05）。New-V组的r值误差比其他两组小。分次间误差波动性分析显示，z和r方向各组比较，差异有统计学意义（F=3.166，P〈0.05），New-V组在4个方向上波动性较小。根据摆位误差分布，对误差引起中心偏移量进行估计，其引起计划靶区（PTV）的剂量分布差异统计显示，New-V组在最小剂量和平均剂量上差异较小，且最小剂量差异有统计学意义（F=8.018，P〈0.05）。结论 New-V组的固定方式较平板（N组）和普通真空垫（V组）固定方式摆位误差、照射分次间误差波动性较小，相对位置误差引起潜在PTV剂量变化较小。因此，新型定制真空垫可优化摆位精度，改善治疗效果。

Objective To evaluate the performance of a customized vacuum-form body immobilization method in the radiotherapy of pelvic malignancies by comparing it with conventional approaches, thus to improve immobilization accuracy in the radiotherapy of pelvic malignancies. MethodsA total of 66 patients with pelvic malignancies were enrolled in this study. These patients were divided into three groups according to three immobilization approaches：radiotherapy board （Group N）, conventional vacuum cushion （Group V）, and a customized vacuum cushion specifically for pelvic immobilization （Group New-V）. Setup deviations of these immobilizations were comparatively evaluated by translational and rotational errors during intra-fractional measurements. Results The average translational setup errors in vertical（x）, longitudinal（y）, lateral（z） and rotational error r were （0.35±0.37）, （0.21±0.22）, （0.29±0.28） cm and （0.70±0.65）° for Group New-V; （0.44±0.43）, （0.31±0.62）, （0.45±0.60） cm and （1.25±1.00）° for Group N; （0.38±0.36）, （0.27±0.25）, （0.32±0.29） cm and （1.09±0.77）° for Group V, respectively. Significant differences were observed in r direction among these three method （F=7.859,P〈0.05）.Group New-V with customized cushion showed the least standard deviations in four directions and the least setup error in r direction compared with the other two method （F=3.166,P〈0.05）. Reconstructed dose distribution based on the isocenter shift result ed from setup errors revealed that Group New-V showed the least deviations in the minimum and mean dose and of the planning target volume （PTV） before and after isocenter shift（F=8.018, P〈0.05）. Conclusions The customized vacuum cushion provided best immobilization and dosimetric advantage. It helps to optimize the immobilization accuracy and improve the clinic outcome potentially.