基于Varian clinac-IX直线加速器放疗系统的技术分析和临床剂量学研究

发布时间：2018-05-25 03:37

本文选题：Varian + clinac-IX加速器　；参考：《南京航空航天大学》2016年博士论文

【摘要】：放射治疗的理想目标是仅在肿瘤部位产生剂量沉积,而正常器官组织无剂量沉积。现代放疗技术虽然还没有达到此种水平,但计算机技术的发展所带来的现代精确放疗技术朝此理想化目标跨越了一大步。精确放疗其核心在于“精确定位、精确计划设计、精确治疗”。为实现精确放射治疗,在放射物理层面需要解决以下三个问题:如何确保放射剂量投射准确;针对不同肿瘤患者选择最优的放射治疗技术,如何设计出最优化的放射治疗计划;以及如何确保放射治疗计划能准确实施。本文旨在利用江苏省苏北人民医院放疗科Varian clinac-IX医用电子直线加速器,及配套使用的Varian Eclipse放射治疗计划系统、指型电离室、MatriXX剂量仪、二维电离室矩阵和COMPASS三维验证系统等设备所构成的完整放射治疗体系,对以上三方面的问题分别展开研究。研究内容和结论如下:首先,为确保射线投射准确,从以下四个方面进行了研究:(1)对高能X射线和电子束在水中吸收剂量的测量与计算方法进行研究,确保射线“质”的准确。研究结果表明,用指型电离室在水模体中测量,并使用IAEA(International Atomic Energy Agency)277号报告的计算方法得出在有效测量点的吸收剂量值与标准计算值之间的误差在0.17%~0.54%之间,满足国家规定(≤2.0%)的要求,研究指出了加速器输出射线的能量大小是准确的;(2)研究加速器质量保证工作中常见的三种电离室(0.01 cm~3、0.125 cm~3以及0.6 cm~3)的剂量响应特性,了解其性能特点,确保剂量监测的准确,从而能保证射线出束“量”的准确;(3)研究多叶准直器参数对射线传输的影响,并将这些参数引入到治疗计划系统中,通过TPS计算和实测比较得出,80%等剂量线面积重合度都大于95%,曲线的分离度均小于3 mm,研究指出了测量多叶准直器(Multileaf Collimator,MLC)的参数是保证射线传输和剂量计算准确性的必要条件;(4)研究IGRT全碳纤维治疗床对射线投射的影响,研究结果表明,IGRT全碳纤维治疗床对6 MV X线的衰减因子在0.981~0.997,对15 MV X线的衰减因子在0.984~0.999,所以设计放疗计划时必须使用虚拟床模式,确保当加速器机架旋转至IGRT全碳纤维治疗床的斜下方或正下方时,治疗床对射线的衰减可以得到与治疗计划系统(treatment planning system,TPS)的补偿修正,保证射线投射准确。其次,针对三维适形放疗、固定野调强放疗和容积旋转调强放疗这三种目前主流的放疗技术,分别以头颈部的鼻咽癌、胸部的乳腺癌、腹部盆腔的宫颈癌、多中心放疗的全中枢神经系统放疗以及危机器官在治疗靶区内的保护海马的全脑照射为例,进行放疗技术的比较剂量学研究,其中鼻咽癌、宫颈癌以及海马保护全脑照射都是进行调强和旋转容积调强放疗两种放疗技术的剂量学参数比较研究,而乳腺癌则是这三种放疗技术的剂量学参数比较研究,全中枢神经系统则采用三维适形放疗和调强放疗比较研究。研究结果表明,旋转容积调强放疗技术能获得更好的靶区剂量分布和更低的危及器官剂量受量,同时治疗跳数MU和治疗时间T更短,但旋转容积调强放疗技术对加速器自身的稳定性要求较高,并且优化过程耗时较长,降低了治疗的效率。另一方面,以宫颈癌5野调强计划为例,研究四组条件变量对剂量学参数的影响,这些条件变量包括X线能量(6 MV和15 MV)、治疗体位(仰卧位和俯卧位)、MLC调强方式(动态和静态)、剂量计算算法包括各向异性分析算法和笔形束卷积算法,研究结果表明,最佳的条件变量应是俯卧体位、各向异性算法(Anisotropic Analytical Algorithm,AAA)剂量算法、MLC动态调强滑窗以及能量为15 MV的高能X线。最后,分析剂量验证和位置验证的必要性。一方面,利用德国IBA公司的MatriXX、COMPASS剂量验证系统的技术优势,以食管癌为例进行剂量验证研究。研究结果表明,食管癌等中心处绝对剂量能够很好的与TPS达到一致;靶区和危及器官的γ通过率均在97%以上,从PD(Percent Different)值来看,GTV(Gross Tumor Volume)、CTV(Clinical Target Volume)、PTV(Planning Target Volume)的D95%、Dmean平均差异在2%以内;脊髓D1%平均差异2.04%;左肺和右肺的V5-30以V10为界差异呈逐渐增大趋势,处于1.5%以内;心脏V20-40差异也呈逐渐增大趋势,平均值差异为2.68%。另一方面,通过分析千伏级的锥形束计算机断层扫描的技术优势,并以肺癌容积旋转调强(Volumetric Modulated Arc Therapy,VMAT)计划为例进行位置验证研究。研究结果表明,.患者在x、y、z轴上的平均摆位误差分别为(0.05±0.16)、(0.09±0.32)、(-0.02±0.13)cm;系统误差在左右、头脚、前后方向分别为:0.28、0.37、0.25 cm;随机误差左右、头脚、前后方向分别为0.16 cm、0.32 cm、0.13 cm;CTV在x、y、z三个方向上的外扩值分别为0.82 cm、1.16 cm、0.72 cm。总之,在射线投射准确性方面,本文的研究结果解释了Varian clinac-IX加速器系统在哪些方面是如何对射线的准确投射产生影响,而了解这种影响是进行精确放疗的基础;在计划优化设计方面,本文的研究结果解决了各种典型病例的计划最优化设计方法,即获得满意的靶区剂量分布的同时,大大降低了危及器官和正常组织的受量;在剂量验证和位置验证研究方面,本文的研究分析了验证的必要性,提供了临床上验证的具体方法,可为临床肿瘤放射物理应用方面提供参考依据。
[Abstract]:The ideal target of radiation therapy is to produce dose deposition only in the tumor site, and the normal organ tissue is no dosed. Although modern radiotherapy technology has not yet reached this level, the modern precise radiotherapy technology brought by the development of computer technology has made a great stride in this ideal target. The core of accurate radiotherapy is "fine determination". In order to achieve accurate radiation therapy, the physical level of radiation needs to solve three problems: how to ensure accurate radiation dose projection, how to select optimal radiotherapy for different cancer patients, how to design the optimal radiotherapy plan, and how to ensure the radiation therapy plan The purpose of this study is to make use of the Varian clinac-IX medical electronic linear accelerator of the Jiangsu Subei People's Hospital, and the Varian Eclipse radiotherapy planning system, the integrated radiation therapy system, such as the type ionization chamber, the MatriXX dosimeter, the two-dimensional ionization chamber matrix and the COMPASS three-dimensional verification system, and so on. The following three aspects are studied respectively. The contents and conclusions are as follows: first, to ensure the accuracy of the ray projection, the following four aspects are studied: (1) the measurement and calculation of the absorption dose of high energy X rays and electron beams in the water are studied to ensure the accuracy of the line "quality". The results show that the finger type ionization is used. The chamber is measured in the water body and uses the calculation method of IAEA (International Atomic Energy Agency) 277 report to conclude that the error between the absorbed dose value of the effective measurement point and the standard calculated value is between 0.17%~0.54%, and satisfies the requirements of the national regulations (less than 2%), and the study indicates that the energy of the output ray of the accelerator is accurate. 2) to study the dose response characteristics of three kinds of ionization chambers (0.01 cm~3,0.125 cm~3 and 0.6 cm~3) common in the quality assurance work of the accelerator, to understand its performance characteristics, to ensure the accuracy of the dose monitoring, and to ensure the accuracy of the ray emission "quantity"; (3) to study the influence of the parameters of the multi leaf straightener on the ray transmission, and to introduce these parameters into the system. In the treatment planning system, through the comparison of TPS calculation and measurement, the area recoincidence of 80% equal dose lines is more than 95% and the separation degree of the curve is less than 3 mm. The study indicates that the parameters of measuring the Multileaf Collimator (MLC) are the necessary conditions to ensure the accuracy of the ray transmission and dose calculation; (4) the study of the treatment of IGRT total carbon fiber treatment. The effect of bed on radiographic projection shows that the attenuation factor of the IGRT total carbon fiber treatment bed for 6 MV X ray is at 0.981~0.997, and the attenuation factor for 15 MV x x is 0.984~0.999, so the virtual bed mode must be used when designing the radiotherapy plan to ensure that when the accelerator frame rotates below the IGRT full carbon fiber treatment bed, it is under or right below. The radiation attenuation of the treatment bed can be compensated with the compensation correction of the treatment planning system (TPS) to ensure the accuracy of the ray projection. Secondly, three current mainstream radiotherapy techniques, such as three-dimensional conformal radiotherapy, fixed field intensity modulated radiation therapy and volume rotation intensity modulated radiation therapy, are used in the head and neck nasopharyngeal carcinoma and breast breast cancer, respectively. Cervical cancer of the pelvic cavity, the whole central nervous system radiotherapy with multi center radiotherapy, and the whole brain irradiation of the crisis organs in the target area for the protection of the whole brain of the hippocampus, the comparative dosimetry study of the radiotherapy technology is carried out. The two kinds of radiation therapy for nasopharyngeal carcinoma, cervical cancer and the whole brain irradiation of the hippocampus are both intensity modulated and rotating volume intensity modulated radiation therapy. The dosimetry parameters of the technology are compared, while breast cancer is a comparative study of the dosimetry parameters of these three kinds of radiotherapy techniques, and the whole central nervous system is compared with three dimensional conformal radiotherapy and intensity modulated radiation therapy. The results show that the rotational volume intensity modulated radiation therapy can obtain better target dose distribution and lower endanger organ dose. At the same time, the dose of MU and the treatment time T are shorter, but the rotation volume intensity modulated radiation therapy has a high requirement for the stability of the accelerator itself, and the optimization process takes a long time and reduces the efficiency of the treatment. On the other hand, the effect of the four condition variables on the dosimetric parameters is studied with the 5 field intensity adjustment plan of cervical cancer. These conditions change. The amount of X-ray energy (6 MV and 15 MV), the treatment of body position (supine position and prone position), MLC intensity modulation (dynamic and static), the dose calculation algorithm including the anisotropic analysis algorithm and the pen convolution algorithm. The results show that the best condition variable should be the prone body position, the anisotropy algorithm (Anisotropic Analytical Algorithm, AAA) dose The algorithm, MLC dynamic sliding window and high energy X-ray with energy of 15 MV. Finally, it analyzes the necessity of dose verification and location verification. On the one hand, using the technical advantage of the MatriXX, COMPASS dose verification system of the German IBA company, a dose verification study is conducted in the case of esophageal cancer. The results show that the absolute dose at the center of esophageal cancer can be done. The rate of gamma passing in the target area and endanger organ was above 97%. From the value of PD (Percent Different), the average difference between GTV (Gross Tumor Volume) and CTV (Clinical Target Volume) was within 2%; the average difference between the spinal cord and the left lung and the right lung was 2.04%. The trend of V20-40 is within 1.5%, and the difference in heart is also gradually increasing. The difference of the average value is 2.68%. on the other hand, by analyzing the technical advantage of the cone beam computed tomography of the kilovolt level, and using the Volumetric Modulated Arc Therapy, VMAT program as an example for the research of the position verification. The results showed that the average error of the patient on the X, y and Z axis was (0.05 + 0.16), (0.09 + 0.32) and (-0.02 + 0.13) cm, the system error was around, the head and foot were 0.28,0.37,0.25 cm, the random error was left and right, the head and foot were divided into 0.16 cm, 0.32 cm, 0.13 cm, CTV in X, and 0.8, 0.8 2 cm, 1.16 cm, 0.72 cm. in all, in terms of the accuracy of the ray projection, the results of this article explain how the Varian clinac-IX accelerator system has an effect on the accurate projection of the ray, and the understanding of this effect is the basis for accurate radiotherapy; in the planned optimization design, the results of this paper have solved a variety of results. The optimal design method of a typical case, that is, to obtain a satisfactory dose distribution of the target area, greatly reduces the amount of endanger organs and normal tissues. In the field of dose verification and location verification, this study analyses the necessity of validation and provides a specific clinical validation method for clinical tumor radiation physics. Provide reference for the application.
【学位授予单位】：南京航空航天大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：R730.55;TL53

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