100 MeV质子束流品质诊断及剂量测量准确性评估方法研究

质子辐射生物学效应是太空放射生物学和质子束放疗研究的重要基础,可为空间环境下人员的危险性评估以及质子治疗优化设计提供科学依据。依托加速器建立相应的生物样本辐照技术是开展此类研究的前提条件。中国原子能科学研究院最近建立的100 MeV强流质子回旋加速器提供的中能质子束流为目前国内能量最高,特别适合用于太空放射生物学和质子治疗相关研究。本研究中,利用在束和离线等多种手段建立了中能质子束流诊断和剂量测量方法,对加速器引出的100 MeV质子照射野大小、均匀性等束流品质以及剂量测量系统准确性进行了分析和评估。结果表明,对光子剂量响应好的LiF(Mg, Ti)热释光探测器,对90 MeV质子同样具有良好的剂量响应关系,可作为中能质子剂量准确性评估的手段之一。在5.0 cm×5.0 cm照射野范围内,加速器引出的100 MeV质子束流的均匀性好于90%,在线剂量测量系统准确性好于93%,束流品质和剂量测量条件基本满足辐射生物学的要求,可为质子辐射生物学效应研究的开展提供可靠保障。     

软调制双散射质子治疗束流配送系统

质子治疗是一种新兴的放射治疗方法,它的主要优点是剂量分布特性优良,可以使高辐射剂量集中于肿瘤部位,减少对周围正常组织的损伤.这一优点的实现主要依靠束流配送系统,它包含质子能量调节与调制、束流扩展和准直等功能.现提出一种新的软调制双散射质子治疗束流配送系统.其特点是利用程序控制质子能量变化以改变质子在体内的射程从而展宽Bragg峰,同时利用两次散射获得较大面积的均匀照射野.它的优点是运行可靠、调节灵活,并特别有利于实现适形治疗.     

质子束治疗中非均匀组织的等效水厚度修正研究

非均匀组织等效水厚度修正是研究质子放射治疗的重要组成部分, 利用蒙特卡罗Fluka2011.2程序模拟了不同能量(50–250 MeV)的质子束入射到不同介质中的输运过程, 总结出了在不同介质中质子束初始能量与质子束Bragg峰深度关系, 并拟合出质子束在介质中的等效水厚度修正公式. 结果表明, 对不同能量的质子束入射到非均匀组织中, 通过拟合公式计算出Bragg峰深度值与Fluka模拟的质子束Bragg峰的位置相差在1 mm 之内. 如果建立起介质和水的Bragg峰比与电子密度比关系的数据库, 该公式有可能用于临床上的质子放射治疗的剂量计算中. 关键词： 蒙特卡罗 质子治疗 等效水厚度 Bragg 峰     

重离子治疗的物理与生物性能和装置原理

 半个世纪来,放射治疗界一直在寻找一种物理剂量分布良好和生物(物理)效应也好的放射线和粒子。几十年来的临床治疗实践,证实了常用的X射线和电子射线的物理剂量分布和生物(物理)效应都不理想。中子和负π粒子的生物效应虽好,但是物理剂量分布不好,给正常组织带来太大的损害。当前较先进的质子治疗,固有的布拉格峰物理特性能使剂量分布很好,但其生物(物理)效应仅稍高于X射线和电子,对治疗抗阻型和乏氧型的肿瘤细胞还难以奏效。而重离子治疗的物理剂量分布和生物(物理)效应都很理想,因此人们转向研究重离子治疗的可能性。     

利用四维质子束诊治肺肿瘤

对肿瘤细胞常用的是X射线辐射治疗，现在荷兰科学家Engelsman M博士在2005年7月中旬在美国西雅图召开的美国医学物理会议（AAPM）上第一次报告了利用质子束来治疗肺肿瘤方面的工作，他在报告中阐述了使用质子束作辐射治疗的方法，以及在4个病人身上作出的实验效果．他指出，利用质子束治疗的最大优点是既能破坏癌细胞，又不会对健康组织带来任何伤害，因此这是一项辐照治疗方面的有效手段．     

基于磁场调制的质子放疗新方法及其调制机制

提出一种基于磁场调制的质子放射治疗新方法, 探索肿瘤剂量、正常器官剂量与磁场调制方法之间的关联机制, 研究磁场调制质子放疗在器官环绕型肿瘤(肿瘤被正常器官环绕或包围)治疗中的应用。基于蒙特卡罗粒子输运程序Geant4,分别建立了理想器官环绕结构（由若干平行六面体结构组成）和含胰腺肿瘤人体腹部解剖结构两种几何构型。分别对两种几何构型内部施加磁场, 通过改变磁场强度和方向,调制质子束布拉格峰几何位置, 利用质子径迹的磁致偏转效应使质子束绕开正常器官对肿瘤进行照射。 对于理想器官环绕型构型, 磁场调制质子放疗可在保证95%剂量覆盖肿瘤情况下将受质子照射正常器官体积控制在接近于零的极低水平。对于胰腺肿瘤解剖构型, 磁场调制方法可使质子束在调制磁场作用下, 绕过脊髓和肾脏照射肿瘤, 并使肿瘤被95%剂量较好地覆盖。通过磁场调制, 可对质子束布拉格峰几何位置和质子径迹弯曲程度进行调制, 绕过正常器官对肿瘤进行照射,从而最大限度地减少正常器官的受照体积和剂量。     

质子治疗的物理特性和工作原理(下)

 在“质子治疗的物理特性和工作原理(上)”中我们介绍了质子本身物理特性和形成治疗用质子流的物理方法。为实现这种质子治疗,必需有一套比常规X和电子直线加速器复杂,而且规模更大的质子治疗系统与装置。质子治疗系统是由许多分系统组使质子束射程再大一些,照射更深的病灶。每次增加一个ΔE,一直增加到E2能量(对应为SOBP的后峰时)才能照射到肿瘤的最深层。这种将质子束变为I(E,t),使能量由E1逐步增加能量步距ΔE直到E2能量的装置,叫能量调制器。由于在最深处肿瘤成,每一个分系统又由许多专用设备,都要涉及专门的技术与学科。     

质子辐照对MQ硅树脂增强的加成型硅橡胶质损及热性能的影响

 采用空间综合辐照模拟设备研究了100 keV和150 keV能量的质子辐照对MQ硅树脂增强的加成型硅橡胶的损伤及其对硅橡胶热性能的影响。试验结果表明：质子辐照后，硅橡胶表面出现损伤裂纹，随辐照能量和剂量的增加，裂纹的数量增多，裂纹增大；质子辐照后，硅橡胶的质量有所损失，其质损率随辐照能量和剂量的增加而增加；质子辐照后硅橡胶的耐热性随辐照剂量的增加先略有增加而后下降，经辐照后的硅橡胶在玻璃态和玻璃转变区的温度区间内收缩率降低，而在高弹态的温度区间内膨胀率增加。     

适用于适形治疗与调强治疗的质子束流配送系统

描述一个适用于适形治疗和调强治疗的散射式质子束流配送系统.它利用双散射系统扩展质子束,利用程序控制的二进制射程调节器和搓板式调制器调节和调制质子射程,利用程序控制的多叶光阑和为每个患者特制的准直器进行束流准直.     

质子辐照空间级硅橡胶的正电子淹没寿命谱研究

 用正电子淹没寿命谱方法（PALS）研究了质子辐照对空间级硅橡胶KH-L-Y微观结构的影响。试验结果表明，PALS谱所揭示的最长寿命成分的t₃, I₃及自由体积分数Vf随辐照剂量的增加开始明显下降；而当辐照剂量大于10¹⁵cm^-2后，随剂量的增加平缓上升。辐照剂量小于10¹⁵cm^-2时，质子辐照使硅橡胶自由体积减小，分子链间堆砌紧密；辐照剂量大于10¹⁵cm^-2时，质子辐照使硅橡胶自由体积增大。交联密度及DMA测试结果同样表明，质子辐照在剂量较小时硅橡胶的交联密度及玻璃化转变温度增加，辐照以交联效应为主；而剂量较大时辐照降解占优势。     

A dose comparison of proton radiotherapy and photon radiotherapy for pediatric brain tumor

The purpose of this study was to investigate the effectiveness of photon radiotherapy and to compare the dose of treatment planning between proton radiotherapy and 3D conformal radiation therapy (3D-CRT) for pediatric brain tumor patients. This study was conducted in five pediatric brain tumor patients who underwent craniospinal irradiation treatment from October 2013 to April 2014 in the hospital. The study compared organs at risk (OARs) by assessing the dose distribution of normal tissue from the proton plan and 3D-CRT. Furthermore, this study assessed the treatment plans by looking at the homogeneity index (HI) and conformity index (CI). As a result, the study revealed OARs due to the small volume proton radiotherapy dose distribution in the normal tissue. Also, by comparing HI and CI between the 3D-CRT and proton radiotherapy plan, the study found that the dose of proton radiotherapy plan was homogenized. When conducting 3D-CRT and proton radiotherapy in a dose–volume histogram comparison, the dose of distribution turned out to be low. Consequently, proton radiotherapy is used for protecting the normal tissue, and is used in tumor tissue as a homogenized dose for effective treatment.     

A study on quantitative analysis of field size and dose by using gating system in 4D conformal radiation treatment

This study evaluated the gating-based 4-D conformal radiation therapy (4D-CT) treatment planning by a comparison with the common 3-D conformal radiation therapy (3D-CT) treatment planning and examined the change in treatment field size and dose to the tumors and adjacent normal tissues because an unnecessary dose is also included in the 3-D treatment planning for the radiation treatment of tumors in the chest and abdomen. The 3D-CT and gating-based 4D-CT images were obtained from patients who had undergone radiation treatment for chest and abdomen tumors in the oncology department. After establishing a treatment plan, the CT treatment and planning system were used to measure the change in field size for analysis. A dose volume histogram (DVH) was used to calculate the appropriate dose to planning target volume (PTV) tumors and adjacent normal tissue. The difference in the treatment volume of the chest was 0.6 and 0.83 cm on the X- and Y-axis, respectively, for the gross tumor volume (GTV). Accordingly, the values in the 4D-CT treatment planning were smaller and the dose was more concentrated by 2.7% and 0.9% on the GTV and clinical target volume (CTV), respectively. The normal tissues in the surrounding normal tissues were reduced by 3.0%, 7.2%, 0.4%, 1.7%, 2.6% and 0.2% in the bronchus, chest wall, esophagus, heart, lung and spinal cord, respectively. The difference in the treatment volume of the abdomen was 0.72 cm on the X-axis and 0.51 cm on the Y-axis for the GTV; and 1.06 cm on the X-axis and 1.85 cm on the Y-axis for the PTV. Therefore, the values in the 4D-CT treatment planning were smaller. The dose was concentrated by 6.8% and 4.3% on the GTV and PTV, respectively, whereas the adjacent normal tissues in the cord, Lt. kidney, Rt. kidney, small bowels and whole liver were reduced by 3.2%, 4.2%, 1.5%, 6.2% and 12.7%, respectively. The treatment field size was smaller in volume in the case of the 4D-CT treatment planning. In the DVH, the 4D-CT treatment planning showed a higher dose concentration on the part to be treated than the 3D-CT treatment planning with a lower dose to the adjacent normal tissues. Overall, the gating-based 4D-CT treatment planning is believed to be more helpful than the 3D-CT treatment planning.     

Evaluation of neutron production in new accelerators for radiotherapy

Ambient dose equivalent, H*(10), and personal dose equivalent, Hp(10), were calculated in different points located inside two different treatment rooms. 15-MV Varian and 15-MV Elekta accelerators were used in these studies. The geometry of both accelerators heads and treatment rooms were built up to perform the Monte Carlo simulations. The patient was also simulated using an ICRU phantom. Calculations were done using the MCNPX code. Ambient dose equivalents rates from neutrons range between 1.2 and 419 mSv/h in the Elekta treatment room and between 0.96 and 1140 mSv/h in the Varian treatment room, depending on the location. These values suggest a larger neutron production in the Varian than in the Elekta accelerator.     

Dosimetric verification of treatment planning system superficial dose calculations for proton beam

To investigate the accuracy of Eclipse treatment planning system (TPS) dose calculations at the surface. It is desirable to know the accuracy of the proton treatment planning system in predicting dose at superficial region. All measurements were performed in a clinical proton beam at the National Cancer Center in Korea. Proton treatment plans were developed for a superficial planning target volume (PTV) contoured on a cylindrical polymethylmethacrylate phantom specially designed for this study. Dose was then measured at the surface and also in the PTV for these treatment plans and compared against the TPS calculations. For our study, a model GD-301 glass dosimeters were used. The proton treatment planning system overestimated the superficial dose without use of bolus as much as by 7–14% when compared to glass dosimeter. On the other hand, with use of bolus to cover the superficial region, surface dose between the calculation from Eclipse and measurement using the glass dosimeter are approximately within 3%.     

Measurement of rectum dose by in vivo alanine/ESR dosimetry in gynecological 192Ir HDR brachytherapy

High dose rate (HDR) brachytherapy (BT) used in treatments of gynecological cancer often results in high doses in the pelvic organs at risk (OARs) and the complications in the rectum are a serious concern. Dosimetry procedures in vivo can be used as an evaluation method of calculated dose in treatment planning. One dosimetric method is the use of alanine with electron spin resonance (ESR) that has been used in different clinical practices. The aim of this study was to indicate the dose level in the female rectum volume, using alanine dosimeters during ¹⁹²Ir HDR gynecological BT, for cervical cancer. Doses were compared with the values obtained using the computational treatment planning system based on two orthogonal radiographic images. Firstly a phantom study in water was performed, enabling the in vivo study. Ten patients had the dose in rectum measured, resulting from 10 points properly referred; variations found were in the range of +60% and −50% of the delivered doses compared to the treatment planning system. Differences between planned and measured doses can be mainly due to uncertainty of dosimeter position determination, averaging of dose points specified over the whole dosimeter position, uncontrolled changes in detector position during treatment due to rectum movement and to a simplified treatment system planning, that do not take into account the details of the patient anatomy and the difference among the tissues. Results show that improvements of the protocol treatment should be done to enhance the relation between treatment planning system and experimental results, nevertheless the dose at the OARs was lower than the recommended by the ICRU Report 38.     

Treatment verification and in vivo dosimetry for total body irradiation using thermoluminescent and semiconductor detectors

The objective of this work is the characterization of thermoluminescent and semiconductor detectors and their applications in treatment verification and in vivo dosimetry for total body irradiation (TBI) technique. Dose measurements of TBI treatment simulation performed with thermoluminescent detectors inserted in the holes of a “Rando anthropomorphic phantom” showed agreement with the prescribed dose. For regions of the upper and lower chest where thermoluminescent detectors received higher doses it was recommended the use of compensating dose in clinic. The results of in vivo entrance dose measurements for three patients are presented. The maximum percentual deviation between the measurements and the prescribed dose was 3.6%, which is consistent with the action level recommended by the International Commission on Radiation Units and Measurements (ICRU), i.e., ±5%. The present work to test the applicability of a thermoluminescent dosimetric system and of a semiconductor dosimetric system for performing treatment verification and in vivo dose measurements in TBI techniques demonstrated the value of these methods and the applicability as a part of a quality assurance program in TBI treatments.     

重离子加速器示范装置被动式束流配送系统次级中子特征的蒙特卡罗研究

在碳离子放射治疗中,碳离子束在剂量配送过程中会与束流输运线相互作用,形成以中子辐射为主的外辐射场.由于中子是高LET射线,具有较高的相对生物学效应,减少碳离子放疗中产生的次级中子有助于降低放疗后正常组织并发症几率及二次肿瘤风险.利用蒙特卡罗方法对保守情况(能量为400 MeV/u,多叶光栅完全闭合)下碳离子治疗被动式束...     

弧形调强放射治疗对剂量计算方法的要求

在弧形调强放射治疗的治疗计划设计中, 由于包含有很多照射方向, 调强最优化的射束元矩阵计算需要很大的计算量和存储量, 为提高计算效率常使用简化剂量计算模型计算射束元矩阵, 因此有必要研究简化模型对治疗计划质量产生影响。 对一个模拟例子和一个临床实例, 使用没考虑散射效应的原射线剂量计算模型计算射束元矩阵, 由此进行最优化计算。 在得到最优化强度分布后, 通过比较原射线剂量计算模型和微分卷积剂量计算模型得到的剂量分布, 研究了不同射束数目条件下, 使用简化剂量计算模型计算射束元剂量矩阵对最终的剂量分布质量的影响。 结果表明, 在射线束很多的情况下(对应弧形调强照射）, 用简化的剂量计算模型, 即不考虑散射来计算射束元剂量矩阵, 会导致靶区剂量分布的质量大大低于预期的剂量分布质量, 因此, 弧形调强放射治疗的最优化计算中, 有效考虑散射的影响是必要的。 In the treatment planning for arc intensity modulated radiation therapy, because many irradiation directions are involved, the computing time and storage space needed for calculating beamlet dose matrices in optimization is quite heavy. In order to improve the computation efficiency, the simplified dose calculation is often used for the calculation of the dose matrices. Thus, it is deserved to study how this simplification could influence the quality of the treatment plan. In this paper, a simulation and a clinical case are adopted. Using the primary dose calculation model without taking into account the scattering effect to generate the dose matrices of beamlets, the optimization for beam intensity profile are firstly carried out. Then, based on the obtained intensity profile, the dose distributions are recalculated by using the primary dose calculation model and the differential convolution superposition dose calculation model which is more accurate but more time consuming. By comparing dose distributions obtained by this two models, the influence of using simplified model for dose matrix calculation on beam profile optimization is studied. The results demonstrate that when the beam number is large(corresponding to the arc modulated radiation), using the simplified model for the calculation of dose matrix of beamlets will reduce the quality of dose distribution greatly comparing with the expected dose distribution quality. Thus it is very necessary to correctly take into account the scattering effect in beam profile optimization for the arc intensity modulated radiation therapy.     

基于混合Batho修正的RBM剂量计算方法在仿真头模实验中的剂量学验证

基于混合Batho修正的规则束模型剂量计算方法可以根据放射治疗过程中加速器相关物理参数和从病人的医学影像数据中获取的人体组织非均匀信息计算出人体内的剂量场数据。在简要介绍该方法的基础上,通过将其计算结果与仿真头模的实测结果进行对比,初步证明了该方法可以作为一种较为可靠的快速剂量计算方法供临床治疗计划系统使用。The dose distribution can be calculated by the Regular Beam Model （RBM） dose engine based on the accelerator parameters and the inhomogeneity data of the patient for the radiotherapy planning. In this paper, the newly-developed mixed Batho correction based RBM is introduced, and then the calculation results are compared with the measured ones using the head phantom. The results demonstrate that the RBM dose engine can be used as a kind of reliable fast dose calculation tool in the clinical treatment planning system.     

碳离子治疗计划中的RBE加权剂量鲁棒优化方法

提出基于混合束模型的相对生物学效应(RBE)加权剂量鲁棒优化方法,用于减少碳离子束射程和摆位偏差对生物剂量分布的影响。建立概率组合鲁棒优化模型,利用二次型目标函数表达式,分别制定针对物理吸收剂量和RBE加权剂量的碳离子束治疗计划,并基于共轭梯度优化算法求解出各自最优的权重解,使得靶区和危及器官(OAR)实际剂量分布在射程和摆位偏差组合情况下尽量满足剂量要求。采用C型靶模型测试鲁棒优化方法的有效性。与基于计划靶区(PTV)的常规优化方法相比,针对物理吸收剂量的鲁棒优化计划临床靶区(CTV)的$ \Delta {D}_{95{\text{%}} } $减少10.00 cGy,OAR的$ \Delta {D}_{5{\text{%}} } $和$ \Delta {D}_{\mathrm{m}\mathrm{a}\mathrm{x}} $分别减少21.50和35.97 cGy,计划的鲁棒性得到了很好的提升。针对RBE加权剂量的鲁棒优化计划CTV的$ \Delta {D}_{95{\text{%}} } $降低14.00 cGy(RBE),OAR的$ \Delta {D}_{5{\text{%}} } $和$ \Delta {D}_{\mathrm{m}\mathrm{a}\mathrm{x}} $分别减少19.00和26.28 cGy(RBE),说明该方法不仅减少了CTV的生物剂量变化,也减少了OAR的生物剂量热点。该结果证明了基于混合束模型的RBE加权剂量鲁棒优化方法在有效提高碳离子放疗计划鲁棒性的同时使OAR也得到了很好的保护。