移动滑轨在椎体瘤调强放疗计划中的动态剂量扰动

目的 研究Qfix kVue治疗床移动滑轨在椎体瘤调强放射治疗(IMRT)计划中的动态剂量扰动。方法 移除EDGE直线加速器碳基绝缘滑轨,进行CT扫描并上传至治疗计划系统,重建床板和滑轨模型。依据均质模体和非均质患者CT,分别制作6和10 MV光子IMRT计划(180°、200°、220°、160°、140°),处方剂量为3 Gy/次,共10次,采用AcruosXB计算剂量。分别制作无滑轨和双侧滑轨对称移动(4~19 cm,步长1 cm)的优化计划。在优化计划中添加、移除滑轨结构,创建验证计划。对比分析验证计划和优化计划的差异,包括靶区平均剂量(D_mean)、均匀性指数(HI)、适形度指数(CI)和脊髓最大剂量(D_max)。结果 有无滑轨患者靶区HI均变差,其最大差值为2%。6 MV有滑轨时患者靶区D_mean减少(2.07±0.99)%,靶区CI值增加(4.91±3.12)%,脊髓D_max减少(1.83±1.37)%。无滑轨时患者靶区D_mean增加(2.02±0.96)%,靶区CI减少(3.07±1.31)%,脊髓D_max增加(2.03±1.44)%。移除和添加滑轨组间,靶区D_mean、CI和脊髓D_max差值差异有统计学意义(F=27.55、361.32、13.05,P<0.05)。靶区D_mean和脊髓D_max随滑轨位置变化呈倾斜的"W"减少。在滑轨＜10 cm范围内,差值出现极大值。当滑轨向外侧移动时,差值逐渐减小为0,6 MV计划中靶区D_mean和脊髓D_max变化值＞10 MV。结论 Qfix kVue治疗床滑轨位置变化对椎体瘤IMRT计划扰动不可忽略,计划制作时应予以考虑,治疗时滑轨应与计划位置保持一致。

Dynamic assessment of the dose perturbation by sliding rails in intensity-modulated radiotherapy for spinal metastases

Objective To investigate the impact of carbon based non-conductive sliding rails on intensity-modulated radiation therapy (IMRT) planning for vertebral tumors.Methods A reconstruction imaging of the couch plate and its rails removed from the EDGE linear accelerator was acquired by helical computed tomography (CT), and pushed into the treatment planning system (TPS). Based on CT images of homogeneous phantom and patients in our database, 6 and 10 MV photon IMRT plans were designed with five fields (180°, 200°, 220°, 160°, 140°), setting a prescribed dose of 3 Gy/F ×10 F to the planning target volume (PTV), and the dose was calculated by AcruosXB. In addition, optimization plans (OP) without rails and with rails symmetrically moving (4-19 cm, step size 1 cm) were created and verification plans(VP) were created by inserting and removing slide rail''s structure from the corresponding OP in VP. The differences in mean dose (D_mean), homogeneity index (HI), and conformability index (CI) of the PTV, and maximum dose (D_max) of the spinal cord were compared and analyzed between the VP and OP.Results HI of PTV with and without the rails were worse in the 6/10 MV verification plans, with a maximum difference of 2%. In 6 MV plans, with rails D_mean of PTV decreased by (2.07±0.99)%,CI increased by (4.91±3.12)%,and D_max of spinal cord decreased by (1.83±1.37)%. Without rails, the D_mean of PTV increased by (2.02±0.96)%, but CI decreased by (3.07±1.31)% and D_max of the spinal cord increased by (2.03±1.44)% in the patient respectively. There were significant statistical differences between groupswith and without rails(F=27.55, 361.32, 13.05,P<0.05).The target volume D_mean and spinal cord D_max decreased with a sloping "W" with the change of the rail position. The difference appeared to be noticeable in the range of less than 10 cm, but it gradually decreased as the rails slid to the outside until it reached zero, and the D_mean of PTV and D_max of the spinal cordchanges were less in 10 MV plans, comparing to 6 MV plans.Conclusions The dose attenuation by the sliding rails of the Qfix kVue should not ignored in the IMRT of spinal metastases and the slide position should be consistent with the planned position.