肺癌精确放疗中计划靶区外扩边界数学模型的建立研究

Research on Mathematical Model of Expanding Margins of PTV in Precise Radiotherapy of Lung Cancer

目的:研究肺癌精确放疗中计划靶区(PTV)外扩边界的影响因素及其数学模型的建立。方法:肺癌患者在CT扫描结束后,将断层图像输入计划系统进行三维重建,勾画肿瘤靶区。测量患者的肿瘤位置、肿瘤体积、肺体积、性别、年龄、体质量等相关参数。在模拟机下分别拍摄正位、侧位的吸气末和呼气末图像,记录靶区Y2、Y1、X2、X1、Z2、Z1等6个方向的位移数据。采用EPID验证摆位误差,拍摄正位、侧位验证图像并与计划系统相应DDR图像比较,测量X(左右)、Y(前后)、Z(头脚)三维方向上的摆位误差数据。用Spss软件对数据进行多元回归分析,得到靶区位移数学模型和摆位误差数学模型,并合成PTV外扩边界数学模型。结果:根据放射物理学推荐公式σ=σs+σp,δ=K.σ=(0.4～0.8)σ,合成PTV外扩边界数学模型公式。经配对t检验,PTV外扩边界数学模型计算结果与肿瘤边界位移测量结果无统计学差异。结论:在肺癌精确放疗中可以用此数学模型计算PTV外扩边界取值参数。

Objective To investigate the expanding margins influencing factors of PTV and the mathematical model in precise radiotherapy of lung cancer. Methods After scanning, the CT images of patients with lung cancer were imported to the planning systems to reconstruct 3D images, target volume of tumour was delineated, and the position and volume of the tumour, the volume of lung, gender, age, weight and other relevant parameters were recorded. Orthophoria and lateral thoracic X-ray images of the patients lied on the simulated positioner were taken in the end of inspiratory and expiratory phase, then the offset data of target volume in six directions of Y2, Y1, X2, X1, Z2 and Z1 were recorded. The set-up errors were confirmed by comaring the orthophoria and lateral validation images shot by EPID and the DDR images of Planning systems, 3D Set-up errors on data of X（right and left）, Y（anterior-posterior） and Z（head and foot） were measured. The mathematical models of target volume displacement and the models of set-up errors were obtained by muhiple regression analysis using software Spss, then the mathematical model of expanding margins of PTV was synthesized. Results According to radiologieal physics formula δ=δs＋δp and δ=K. σ=（0.4-0.8）σ, the mathematical model of expanding margins of PTV was synthesized. By paired t-test, the mathematical model of expanding margins PTV calculation result and the boundary of the tumours displacement measurement resuhs proved no statistical difference. Conclusion This mathematical model can be used to calculate the expanding margins of PTV values of the parameters in the lung cancer precise radiotherapy.