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目的 探讨“固定头枕”联合“去膝垫”简化体位固定方案对直肠癌仰卧位容积旋转调强放疗(volumetric modulated arc therapy, VMAT)摆位精度的优化作用，以及对计划靶区(planning target volume, PTV)外扩边界的收窄效益。方法 回顾性选取2020年12月至2025年12月在我院接受盆腔VMAT的直肠癌患者53例，根据体位固定辅助装置的不同划分为3组：A组(n=15)采用“非固定头枕+膝垫”固定方案；B组(n=18)采用“固定头枕+膝垫”固定方案；C组(n=20)采用“固定头枕+去膝垫”固定方案。共获取159分次摆位锥形束计算机断层扫描(cone-beam computed tomography, CBCT)数据，收集6个轴向[升降平移(Vrt)、进出平移(Lng)、左右平移(Lat)、进出倾斜(Pitch)、左右转动(Roll)、旋转偏航(Rtn)]的摆位误差，采用单因素方差分析(ANOVA)比较3组患者的个体系统误差mi，采用非参数MannWhitney U检验比较3组的个体随机误差σi。以平移绝对值>5.00 mm或旋转绝对值>2.00°作为摆位异常的判定标准，通过卡方检验分析异常摆位的发生率，利用外扩边界经典公式Margin=2.5Σ+0.7σ计算3个平移轴向上的外扩边界。结果 单因素方差分析显示，3组患者的个体系统误差在Vrt轴向(F=15.89,P<0.01)和Roll轴向(F=3.87,P=0.03)上的差异有统计学意义，C组的个体系统误差均值最逼近零位(Vrt轴向为-0.28 mm,Roll轴向为0.01°)。在群体系统误差Σ方面，C组在Lng轴向(C组1.14 mm vs. A组1.79 mm vs.B组1.98 mm)和Lat轴向(C组1.43 mm vs. A组1.54 mm vs.B组2.84 mm)的离散度显著低于A、B两组。非参数Mann-Whitney U检验显示，C组在Pitch轴向上的个体随机误差明显低于A组(Z=-2.47,P=0.01),B组与其他两组无统计学差异。异常摆位分析显示，C组的异常摆位发生率仅为3.33%，显著低于A组的31.11%和B组的22.22%(χ2=14.87,P<0.01)。在外扩边界方面，C组在Vrt 、Lng、Lat轴向上的外扩边界分别收窄至3.58 mm、5.65 mm和6.47 mm，最高比A组收窄了35.50%。结论 直肠癌仰卧位VMAT中，采用“固定头枕且去除膝垫”的简化体位固定方案可通过稳定脊柱动力链与触发膝关节“旋锁”锁定机制，显著提高摆位几何重复性，有效收窄PTV外扩边界并保护危及器官，推荐作为盆腔放疗的标准化方案。
Abstract：Objective To evaluate the clinical efficacy of an optimized pelvic immobilization protocol—combining a locked headrest with knee wedge removal—on setup accuracy and planning target volume(PTV) margins in rectal cancer patients undergoing VMAT in the supine position. Methods We retrospectively analyzed 159 fractions of cone-beam CT(CBCT) registration data from 53 patients with rectal cancer treated with pelvic volumetric modulated arc therapy(VMAT) between December 2020 and December 2025. Patients were assigned to three cohorts: Group A(n =15) used the “non-fixed headrest + knee wedge” fixation scheme; Group B(n =18) used the “locked headrest + knee wedge” fixation scheme; Group C(n =20) used the “locked headrest + knee wedge removed” fixation scheme. Six-dimensional(Vrt, Lng, Lat, Pitch, Roll, Rtn) setup errors were collected. One-way ANOVA with LSD post-hoc tests and Mann-Whitney U tests were employed to compare individual systematic errors and random errors among the groups. Abnormal setup was defined as any linear shift >5.00 mm or rotation >2.00°. PTV margins in three translational directions were determined using the van Herk formula(Margin = 2.5Σ + 0.7σ). Results One-way ANOVA revealed significant differences in systematic Vrt(F = 15.89, P <0.01) and Roll(F = 3.87, P = 0.03) bias among the three groups with Group C demonstrating systematic means closest to the absolute zero center(Vrt:-0.28 mm, Roll: 0.01°). Group C achieved the lowest group systematic error(Σ) in Lng(1.14 mm vs. 1.79 mm in Group A and 1.98 mm in Group B) and Lat directions(1.43 mm vs. 1.54 mm in Group A and 2.84 mm in Group B). For random errors, Group C achieved significantly smaller Pitch rotational variation compared to Group A(Z =-2.47, P = 0.01). The abnormal setup rate in Group C was 3.33%, significantly lower than 31.11% in Group A and 22.22% in Group B(χ2 = 14.87, P <0.01). PTV margins for Group C in the Vrt, Lng, and Lat directions were safely contracted to 3.58 mm, 5.65 mm, and 6.47 mm, respectively, with the maximum narrowing of 35.50% compared to Group A. Conclusion The optimized pelvic immobilization protocol utilizing a locked headrest and removing the knee wedge significantly enhances the geometric reproducibility of VMAT setups for rectal cancer by stabilizing the spinal kinetic chain and engaging the knee screwing-home mechanism. This cost-free approach effectively compresses PTV margins and enhances organat-risk(OAR) sparing, making it highly recommended as a standardized protocol for supine pelvic radiotherapy.
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基本信息:
DOI：10.11876/mimt202604011
中图分类号:R735.37;R730.55
引用信息:
[1]刘现珍,岳海振,李俊禹,等.体位固定辅助装置优化在直肠癌仰卧位容积旋转调强放疗中的应用价值[J].现代仪器与医疗,2026,32(04):83-91.DOI:10.11876/mimt202604011.
基金信息:
国家重点研发计划（2023YFF0613501）; 北京市自然科学基金资助项目（1202009）
2026-09-15
2026-09-15
2026-09-15