肺癌组织间插植放疗患者靶区运动对脊髓最大剂量的影响

Influence of CTV movement on the maximal dose of spinal cord for patients with lung cancer undergoing interstitial brachytherapy

目的研究肺癌的铱源后装近距离组织间插植照射中靶区的运动对于脊髓剂量的影响。方法以西南医科大学附属医院肿瘤科2016-01-01-2017-01-31收治的10例铱源后装近距离组织间插植照射肺癌患者CT影像资料为基础,分别对每一组CT影像资料勾画9个半径为5 mm的圆柱体模拟脊髓,并设置圆柱体与临床靶区体积(CTV)的距离分别为0、5、10、15、20、25、30、40和50 mm,用于模拟脊髓的距离变化。在SPSS 19.0中采用线性、二次项和指数3种拟合方式分别拟合模拟脊髓最大剂量(Dmax)与随距离变化的曲线,对回归方程和回归参数分别进行F检验和t检验,并比较拟合优度R2。采用积分的方式分析靶区运动对于脊髓剂量的影响。结果 CTV的D95%平均值为(10 054.63±17.52) cGy(10 029.17~10 086.01 cGy),Dmax线性拟合公式为y=-146.17x+6 808.50(R2=0.65,P<0.01),Dmax二次项拟合公式为y=4.75x2-380.24+8 517.08(R2=0.81,P<0.01),Dmax指数拟合公式为y=7708.44e-0.046x(R2=0.90,P<0.01)。脊髓和靶区距离的估算误差会影响Dmax,当距离误差达到1 mm或-1 mm时,对Dmax的影响可达-4.71%和4.50%。同时,靶区运动也会影响Dmax,当运动幅度分别为1、2、3、5、10 mm时,Dmax的影响分别为0.05%、0.21%、0.48%、1.32%和5.29%。结论利用铱源后装机开展肺部肿瘤近距离组织间插植照射时,只读取计划系统中脊髓Dmax进行脊髓剂量的安全评估存在缺陷。评价脊髓Dmax时,应该充分考虑CT图像中靶区运动相位和幅度等因素的影响。

Objective To investigate the influence of clinical target volume(CTV) movement on spinal cord dose in 192-iridium interstitial brachytherapy of lung tissue. Methods CT image data from ten cases of 192-iridium interstitial brachytherapy plans in Department of Oncology, Affiliated Hospital of Southwest Medical University from January 1, 2016 to January 31, 2017 were collected. A total of nine cylinders with a radius of 5 mm were contoured for simulating the spinal volume in each cases;and the cylinders were respectively set at 0, 5, 10, 15, 20, 25, 30, 40 and 50 mm away from the CTV. Linear, quadratic and exponential fitting methods were used to simulate the maximal dose of spinal cord(Dmax) in SPSS 19.0 statistical software. The regression equation and regression parameters were tested by F test and t test, and the goodness of Fit R2 were compared. The effect of target movement on Dmax was analyzed by integral method.Results The dose of 95% CTV(D95%) were(10 054.63±17.52) cGy(10 029.17-10 086.01 cGy). The linear fitting formula of Dmax: y=-146.17x+6 808.50(R2=0.65, P<0.01);the quadratic fitting formula of Dmax: y=4.75x2-380.24+8 517.08(R2=0.81, P<0.01);the exponential fitting formula of Dmax: y=7 708.44 e-0.046x(R2=0.90, P<0.01). The distance error between the spinal cord and the target area would affect the Dmax value. When the distance error was estimated to be 1 mm and-1 mm, the Dmax dose value might be changed by-4.71% and 4.50%. The target motion also affected the Dmax value. When the range of motion of target area was 1, 2, 3, 5 and 10 mm, the different percentage of Dmax was 0.05%, 0.21%, 0.48%, 1.32% and 5.29%, respectively. Conclusion The spinal cord irradiation dose is affected by the uncertainty of the spinal cord location acquired from the CT images in TPS;in order to evaluate spinal cord dose more accurately,we should pay more attention to it.