乳腺癌仿真模体术后胸壁放疗方法的比较研究

目的 使用MOSTET探测器观察分析乳腺癌术后5种常用放疗技术在模体中的剂量分布特点,同时验证TPS计划剂量准确性,为临床治疗方案及技术选择提供剂量学依据。方法 使用高仿真模体模拟成年女子左侧乳腺癌术后患者。对患侧胸壁靶区的代表测量点及其不同深度测量点进行标记定位后,在TPS上分别设计正向IMRT、逆向IMRT、3DCRT、6 MeV电子线、9 MeV电子线照射方案。最后对模体进行模拟照射,并对各点进行实时测量。采用方差分析检验5种方法间总差异。结果 正向IMRT、逆向IMRT、3DCRT、6 MeV电子线、9 MeV电子线实测平均剂量在表面的分别为74.32、69.21、73.97、75.86、81.41 cGy (F=3.36,P<0.05),0.5 cm深度的分别为95.59、93.37、96.78、99.63、94.97 cGy (F=2.40,P>0.05),1.0 cm深度的分别为103.42、102.53、103.48、88.89、101.36 cGy (F=7.19,P<0.05),近胸壁肺的分别为82.74、68.24、85.34、21.49、75.02 cGy (F=46.43,P<0.05)。5种方法的平均剂量偏差在表面的为 －8.04%(－6.57%~－11.93%),0.5 cm深度的为 －1.95%(2.15%~－5.90%),1.0 cm深度的为0.65%(－2.87%~3.22%),近胸壁肺的为 －3.53%(3.90%~－8.93%)。结论 MOSFET探测器配以相应的仿真模体可以测量体内某部位的实际剂量,对放疗QA与QC提供了一种较好方法,亦可用于评价不同放疗技术的剂量学特点。MOSFET探测器适用于乳腺癌放疗的在体剂量监测,指导补偿膜的间隔使用以调整剂量,纠正误差,提高靶区吸收剂量的准确性。     

平行板电离室的校准与电子线剂量测量方法比较

[目的]探讨平行板电离室的三种不同校准方法和校准精度，及电子线测量中不同电离室的应用范围。[方法]分别采用高能电子束校准法、^60Co y射线模体校准法和^60Co γ射线空气校准法平行板电离室进行校准后，测量4～18MeV的加速器高能电子线输出剂量．并与指形电离室测量结果进行比较。[结果]与高能电子束校准法相比，^60Co γ射线模体内校准法得到的平行板电离室空气吸收剂量校准因子数值几乎相等（差别仅为0．27％。），而^60Co γ射线空气校准法差别大于〉2％。指形电离室对6-18MeV的电子束输出剂量测量误差小于0．8％．对4MeV电子束的测量误差则达2．59％。[结论]^60Co γ射线模体校准法与高能电子线校准平行板电离室精度相近，而^60Co γ射线空气校准法误差较大。对能量大于6MeV的电子束，使用指形电离室也能得到较准确的测量结果，但4MeV以下电子束必须使用平行板电离室测量才能满足临床质控要求。     

不同算法在非均匀组织模体中光子剂量计算精确度比较

目的 比较治疗计划系统(TPS)中光子束剂量的筒串卷积算法(CCC)与笔形束卷积算法(PBC)在非均匀组织中的计算精确度。方法 建立2个虚拟肺模型,一个在光子束单前野入射情况下比较两种算法得到的中心轴上的百分深度剂量(PDD);另一个在光子束前后对穿野入射,模体中心有一个肿瘤等效组织,两种算法计算光子束穿过肺等效组织到达肿瘤等效组织时肺和肿瘤等效组织中的剂量分布。两种情况下得到的结果与蒙特卡罗(MC)算法计算的结果进行比较。结果 单前野时,光子束从高密度组织入射到低密度的肺等效组织,与MC算法比较PBC算法高估了肺等效组织中的剂量(t=3.90,P=0.012),CCC 算法与之接近(t=2.25,P=0.087)。前后对穿野时,CCC算法和MC算法计算出的肿瘤等效组织边界剂量都要低于PBC算法的剂量(t=2.43、3.18,P=0.038、0.011),并且能量越高,肺密度越小时,这种差别越大。结论 计算低密度组织中的肿瘤或其后方肿瘤剂量时最好采用CCC算法(如肺癌、食管癌以及胀气的直肠和胃后方肿瘤)。     

商用质子治疗计划系统射程计算精度的验证北大核心CSCD

目的测量并验证商用质子治疗计划系统RayStation V10的计算精度及质子射程的计算精度,为该系统的临床运用提供参考。方法在上海瑞金医院质子治疗装置上,使用仿真头部模体验证RayStation的计算精度,扫描获取模体的CT数据并导入计划系统,追加设置水箱使其紧贴于模体后,在水箱适当深度设置一个立方体靶区,设计处方剂量为200 cGy(相对生物效应)且束流垂直穿过模体的单野验证计划,实施照射后,比较测量结果和计划系统计算结果。结果使用RayStation默认设置制订验证计划时,测量得到的纵向剂量分布相比计算结果往深的方向移动约4 mm,表明RayStation过高估计了模体中组织等效材料的水等效厚度。为研究该误差来源,用实际束流测量模体中软组织等效材料的水等效厚度,根据测量结果,微调RayStation默认设置,发现纵向扩展布拉格峰测量结果和计算结果的误差可以缩小到2 mm。结论使用RayStation默认设置计算仿真模体的阻止本领,可能带来较大射程误差。使用组织分割和实测模体的组织水等效厚度相结合的方法,可改善治疗计划系统在仿真模体上的射程计算精度。此方法有望成为减小此类剂量算法误差的有效手段之一。     

面罩对不同射线治疗剂量影响的探讨

目的：测量在光子线及电子线照射下面罩对治疗剂量的影响。方法：采用PIW Marcus 23343型平行板电离室在专用的有机玻璃模体（PMMA）中测量光子线建成区别剂量的变化情况，采用Bruce等介绍的经验公式对测量结果进行修正，采用三维水箱测量电子线射野中心轴百分深度剂量，并利用平行板电离室对特定深度进行验证，结果：加上面罩后，8MV光子线建成区剂量有明显增加，近表面处相对增加约25％左右，8、12和15MeV的电子线的中心轴百分深度剂量曲线则普遍前移。结论：对于光子线主要考虑的是近表面建成区剂量的改变；对电子线则要考虑由于百分深度量前移而可能影响治疗靶区的最小剂量。三维适放射治疗中要注意治疗治疗计划系统（TPS）的计算结果是否考虑面罩对治疗剂量的影响。     

放疗计划系统中空腔边缘剂量计算准确性研究

目的 研究TPS中CCC、AAA算法在空腔边缘剂量计算的准确性。方法 采用EGSnrc软件包的子程序BEAMnrc用对美国瓦里安Trilogy直线加速器进行了蒙特卡罗模拟,并使用IBA蓝水箱三维扫描系统验证了该Monte Carlo算法的准确性,证实蒙特卡罗算法的可靠性。设计一带有不同大小空腔的等效水模体,分别用CCC、AAA算法计算不同大小空腔的等效水体模的中心轴深度剂量分布和侧向剂量profile。深度方向计算结果与蒙特卡罗算法进行比较,侧向剂量profile计算结果与EBT₂胶片测量结果进行比较。结果 在空腔边缘CCC、AAA算法都高估了剂量。CCC计算精确性优于AAA,但误差依然存在。这种误差主要与计算网格、射野大小、能量、空腔大小、射野数目有关。结论 TPS中的CCC和AAA剂量计算时还应充分考虑到空腔边缘的电子不平衡。     

用二维电离室阵列对螺旋断层治疗的调强计划进行剂量验证

目的 研究采用二维电离室阵列对螺旋断层治疗(HT)的调强计划实施剂量验证的可行性,寻求建立一套临床上针对该条件下患者治疗更为有效的剂量验证方法 .方法 采用IBA公司I'mRT MatriXX二维电离室阵列及其相配套MULTICube等效同体水模体对10例患者HT的调强计划实施验证.分别对二维电离室阵列实行冠状及纵向位测量,并获取模体中阵列轴平面和纵断面剂量分布.通过HT系统兆伏级CT图像实现模体精确配准及校正,以确保二维电离室阵列摆位准确性.束流照射后将二维阵列剂量测量平面分布与HT计划系统模体计划中计算平面结果 进行比较,定性或定量分析其绝对剂最及相对剂量验证情况.探讨其不同位置摆放来实现其测量方法 的可行性.结果 定性或定量分析所测量与计算绝对剂量点及相对剂量分布的结果 均显示出了较好一致性,点绝对测量与计算剂量偏差保持在±3%以内.MatrXX阵列测量的相对剂量分布与治疗计划系统模体中计算平面相比较,采用了Gamma法(3 mm或3%)进行2 mm栅格精度分析,γ≤1像素点平均通过率分别为97.76%、96.83%.结论 MatriXX二维电离室阵列可较好地进行绝对剂量及相对剂量测量,能较好地实现调强计划的剂量验证.     

两种放疗计划系统对仿真体模和患者及均匀体模进行剂量计算结果比较

目的 通过Eclipse与Pinnacle3 V 7.4f两种TPS对仿真体模、患者及均匀组织体模的CT图像进行剂量计算,比较两种TPS进行非均匀组织计算的结果差异,并与均匀体模的结果进行比较.方法 对患者、仿真体模以及均匀体模的CT图像利用两种TPS作相同计划,比较临床常用指标(肺V20和V30计划靶区的D95以及等中心点和等中心层面内8个兴趣点的剂量)的结果差异.结果 对患者及仿真体模而言,虽然两TPS对等中心点剂量计算的结果差异较小,但其他指标却存在较大差异(利用二级准直器照射时患者计划靶区D95的差异最大可达10.17%,仿真体模为4.64%;利用多叶光栅照射时患者计划靶区D95的差异最大达10.74%,仿真体模为5.66%;对于计划靶区边缘1-4点的剂量差异,患者有超过10.00%的情况,仿真体模最大为7.65%;肺V30的差异也较大).而对均匀体模而言,两TPS对各指标的计算差异却较小.结论 两TPS对仿真体模计算的结果差异比患者小,而对患者及仿真体模计算的结果差异要大于对均匀组织体模的.     

电子线斜入射对剂量分布影响的分析

目的　量化分析不同能量电子线在斜入射情况下对剂量分布的影响。方法　在水模体中 ,测量束流中心轴上不同相对剂量值的深度 ;并测量 80 %和 5 0 %等剂量线的倾斜角度 ;将电子线在不同斜入射角度时的这些测量数据与垂直入射时的测量数据进行比较。结果　①电子线斜入射角度越大 ,最大剂量点深度和 90 %、80 %、5 0 %及 10 %的深度越小 ;②能量越高 ,斜入射对最大剂量点深度和 90 %、80 %、5 0 %及 10 %的深度影响越大 ;③斜入射对相对剂量分布的影响还与射野大小有关 ,射野越大 ,最大剂量点深度和 90 %、80 %、5 0 %及 10 %的深度变化越小 ;④在相同的斜入射条件下 ,电子线能量的改变比射野大小的改变对相对剂量分布的影响要大 ;⑤在斜入射时 ,80 %和 5 0 %等剂量线会向有空气隙的一侧倾斜 ,并且倾斜角度要比斜入射角度大。结论　斜入射不仅使最大电离深度值减小 ,而且使电子线穿透能力减弱 ;电子线穿透能力的减弱程度与电子线能量和射野大小有关 ;临床上要充分考虑在斜入射时 80 %和 5 0 %等剂量线的横向移动 ,否则很容易造成肿瘤靶区的漏照射 ,从而导致肿瘤的局部复发。     

IGRT锥形束CT图像的CT值与物理密度关系的研究

目的 通过比较标准物理密度参考模体在IGRT锥形束CT（CBCT）和常规扇形束CT（FBCT）扫描图像的CT值，讨论影响CBCT中密度与CT值对应关系的主要因素。方法 将一种可拆分的带有人体组织等效密度插件的参考模体在IGRT-CBCT和FBCT中选择多档能量、不同视野（FOV）进行扫描，对得到的各密度插件CT值进行比较。结果 IGRT-CBCT获取图像的密度与CT值对应关系受密度体插件的空间位置、模体大小、扫描孔径范围及能量影响明显大于FBCT。在CBCT中，FOV、模体的大小对CT值影响很大。能量越高，CT值受空间位置、FOV大小及不同大小模体的影响越小，能量越高密度对比度越差。结论 由于目前厂家未对CBCT的CT值进行校正，CBCT的CT值不是真正意义上的HU值，不能用于治疗计划系统中的剂量计算。     

Determination of absorbed dose to water for high energy photon and electron beams--comparison of different dosimetry protocols

The determination of absorbed dose to water for high-energy photon and electron beams is performed in Germany according to the dosimetry protocol DIN 6800-2 (1997). At an international level, the main protocols used are the AAPM dosimetry protocol TG-51 (1999) and the IAEA Code of Practice TRS-398 (2000). The present paper systematically compares these three dosimetry protocols, and identifies similarities and differences. The investigations were performed using 4 and 10 MV photon beams, as well as 6, 8, 9, 10, 12 and 14 MeV electron beams. Two cylindrical and two plane-parallel type chambers were used for measurements. In general, the discrepancies among the three protocols were 1.0% for photon beams and 1.6% for electron beams. Comparative measurements in the context of measurement technical control (MTK) with TLD showed a deviation of less than 1.3% between the measurements obtained according to protocols DIN 6800-2 and MTK (exceptions: 4 MV photons with 2.9% and 6 MeV electrons with 2.4%). While only cylindrical chambers were used for photon beams, measurements of electron beams were performed using both cylindrical and plane-parallel chambers (the latter used after a cross-calibration to a cylindrical chamber, as required by the respective dosimetry protocols). Notably, unlike recommended in the corresponding protocols, we found out that cylindrical chambers can be used also for energies from 6 to 10 MeV.     

A reticle retrofit and dosimetric consideration for a linear accelerator

PURPOSE: An imperfect reticle system in an accelerator causes uncertainties in source-skin distance (SSD), off-axis distance (OAD), isocenter, and so forth. A reticle was designed and fabricated, and its implications on x-ray and electron beam dosimetry were investigated. METHODS AND MATERIALS: A new reticle frame was dimensioned to fit snugly in the accelerator. The frame was fabricated to carry a pair of adjustable cross wires and to allow the machine operation in the photon and electron modes. The impact of the cross wires on 6 MV photon and 5-10 MeV electron beam parameters such as dose rate (Gy/monitor unit), beam uniformity, surface dose, and so forth, were studied using suitable ion chambers and phantoms. RESULTS: The retrofitted system offered long-term mechanical stability leading to precise SSD, OAD, and isocenter measurements. Changes introduced by the cross wires on the 6 MV photon and 5-10 MeV electron beams are presented. CONCLUSION: Long-term stability of a reticle in an accelerator is important for an accurate patient setup and for making reliable dosimetric measurements. Beam characteristrics have to be studied whenever modifications on a reticle system are made.     

基于蒙特卡洛方法研究电子线输出因子影响因素

目的 使用蒙特卡洛方法计算电子线输出因子,探讨直线加速器各组成部分对输出因子影响。方法 使用蒙特卡洛MCTP软件模拟瓦里安23EX医用直线加速器6、9、18 MeV电子线,源皮距100 cm下不同射野大小(2 cm×2 cm~25 cm×25 cm)的输出因子。使用Scanditronix Wellhofer Blue Phantom自动扫描系统三维水箱测量相同条件下的输出因子。观察计算与测量结果差异,要求两者<2%。再使用蒙特卡洛方法分别计算不同能量下不同限束系统条件下原粒子和散射粒子的输出因子(包括限光筒、铅门、挡铅的输出因子),并讨论限束系统各个部件对输出因子的影响。结果 MCTP系统计算的6、9、18 MeV电子线输出因子与测量结果间差异<1%。电子线能量、限光筒—铅门—挡铅组合以复杂的方式影响原粒子和散射粒子,从而影响输出因子。 结论 蒙特卡洛MCTP软件能精确计算不同能量下不同限束系统条件下原粒子和散射粒子的输出因子,电子线能量及限束系统以复杂方式影响输出因子。     

Experimental determination of depth-scaling factors and central axis depth dose for clinical electron beams

Depth-scaling factors rho(eff) for clear polystyrene and polymethylmethacrylate (PMMA) phantoms have been determined experimentally as a function of nominal electron-beam energy in the range 6 to 22 MeV. Values of rho(eff) have been calculated from the ratio rho(eff) = R(wat)(50) / R(med)(50), where R(wat)(50) and R(med)(50) are the measured depths of 50% ionization in electron solid water and plastic (clear polystyrene and PMMA) phantoms, respectively. Measurements were made using an Attix chamber in an electron solid water phantom, a Holt chamber in a clear polystyrene phantom, and a Markus chamber in a PMMA phantom. The average value of measured rho(poly)(eff) was found to be 0.999 +/- 0.009. This is higher than the value of 0.975 recommended by Task Group 25 (TG-25) of the American Association of Physicists in Medicine (AAPM) by 2.5%. Depending on energy, the maximum differences between the AAPM TG-25-recommended and the measured values lie in the range 1% to 3.5%. Similarly, the average value of measured rho(PMMA)(eff) was found to be 1.168 +/- 0.023. This is higher than the AAPM TG-25-recommended value of 1.115, by 5%. Depending on energy, the maximum differences between the AAPM TG-25-recommended and the measured values lie in the range 3% to 8%. Central axis depth dose curves in water were generated for 6, 15, and 20 MeV electron beams from measured depth-ionization data in PMMA and clear polystyrene phantoms following the recommendations of the AAPM TG-25 report and using both TG-25-recommended and experimentally determined values of depth-scaling factors rho(eff). For both phantoms, either the TG-25-recommended value or the experimentally determined values of rho(eff) yielded agreement to within about 2 mm among all depth doses in water at the depths of clinical relevance.     

乳腺癌术后大分割短疗程放疗的远期结果分析

目的研究乳腺癌术后大分割放疗的疗效、疗程和副反应。方法60例乳腺癌术后需放疗病例随机均分为大分割放疗组(HOFRT组)和常规放疗组(CRT组)。两组病例根据TNM分期、腋窝淋巴结转移数等设内乳野、锁腋野、胸壁野。HOFRT组的胸壁野照射采用切线对穿照射,HOFRT组第1、3天为5.0 Gy/次,第15、17天为6.5 Gy/次,共23 Gy分4次17 d完成。CRT组2.0～2.5 Gy/次,共45-50 Gy分20～25次4-5周完成。HOFRT组10例和CRT组9例腋窝后野加量10-15 Gy分5～7次5～7 d完成。HOFRT、CRT组总疗程分别为3.1～3.4、4.7-6.0周。结果HOFRT、CRT组10年总生存率分别接近56%、39%,Ⅲ期10年生存率分别接近41%、52%(P>0.05),局部复发率分别接近13%、10%(P>0.05)。HOFRT和CRT组放疗晚期损伤导致的患肢淋巴水肿、活动受限发生率分别接近23%、3%和11%、7%(P>0.05)。HOFRT组急性2 3级放射性皮肤损伤显著低于CRT组(10%:43%,P<0.01)。结论大分割放疗是一种短疗程、安全、有效的乳腺癌术后放疗方案,局部复发、生存率和晚期副反应与常规放疗无差异,值得进一步研究。     

A comparison of electron beam dose calculation accuracy between treatment planning systems using either a pencil beam or a Monte Carlo algorithm

PURPOSE: To present a comparison of the accuracy of two commercial electron beam treatment planning systems: one uses a Monte Carlo algorithm and the other uses a pencil beam model for dose calculations. METHODS AND MATERIALS: For the same inhomogeneous phantoms and incident beams, measured dose distributions are compared with those predicted by the commercial treatment planning systems at different source-to-surface distances (SSDs). The accuracy of the pencil beam system for monitor unit calculations is also tested at various SSDs. Beam energies of 6-20 MeV are used. RESULTS: The pencil beam model shows some serious limitations in predicting hot and cold spots in inhomogeneous phantoms for small low- or high-density inhomogeneities, especially for low-energy electron beams, such as 9 MeV. Errors (>10%) are seen in predicting high- and low-dose variations for three-dimensional inhomogeneous phantoms. The Monte Carlo calculated results generally agree much better with measurements. CONCLUSIONS: The accuracy of the pencil beam calculations is difficult to predict because it depends on both the inhomogeneity geometry and location. The pencil beam calculations using CADPLAN result in large errors in phantoms containing three-dimensional type inhomogeneities. The Monte Carlo method in Theraplan Plus dose calculation module is shown to be more robust in accurately predicting dose distributions and monitor units under the tested conditions.     

Absorbed dose determination for high energy photon and electron beams at a PRIMUS linear accelerator using the documents DIN 6800-2 and TRS-398

The International Atomic Energy Agency in Vienna has recently published a new Code of Practice for absorbed dose determination in external beam radiotherapy (Technical Reports Series No. 398). This code claims to fulfill the need for a systematic and internationally unfied approach to the calibration of ionization chambers, as well as to the use of these detectors in determining the absorbed dose to water for the radiation beams used in radiotherapy. In Germany, the corresponding national norms are laid down in DIN 6800-2. Therefore, it appeared necessary to compare in detail the procedures and results obtained according to these two documents. The comparison was performed for a 6 MV and 15 MV photon beam, as well as for a 12 MeV and 18 MeV electron beam. Although a series of differences could be ascertained, in particular in the numerical values of the various perturbation factors, the agreement of the final results remained well within the expected uncertainty range. Nevertheless, it is suggested to modify DIN 6800-2 in order to make it more easily applicable to a hospital environment, to incorporate the progress of knowledge in the data involved, and to achieve a better adherence to international recommendations.     

A flatness and calibration monitor for accelerator photon and electron beams

A flatness monitor has been built to quickly and accurately check accelerator beam flatness and dose calibration. Consisting of a 7 X 7 ion chamber array, the unit operates in photon beams from 60Co energies to 25 MV and electron beams (scattered or scanned) from 6 MeV to 25 MeV.     

热塑料面膜对皮肤剂量的影响研究

目的定量研究鼻咽癌放射治疗时,热塑料面膜在与皮肤各种距离的情况下对皮肤剂量及靶区剂量的影响,对使用面膜后皮肤反应加重的临床现象进行探讨.方法使用VARiAN2100C/D加速器产生的X6与E9射线;比利时ORFIT工业公司生产的U-PLAST材料的固定热塑料面膜;半导体探头;DPD-510半导体现场测量仪及Farmer 2570/1剂量仪和258l电离室(0.6cm3)采用源轴距(SAD)和源皮距(SSD)的方法,测量面膜与皮肤不同距离时对皮肤剂量和最大剂量点剂量的影响.结果 (1)X线入射线对皮下2 mm处剂量有一定影响,可提高11%的剂量,电子线(E9)则在面膜与皮肤有一定距离(2～2.5 cm)时产生一个高剂量峰,在皮下2 mm处最大可产生35%左右的剂量增幅.(2)使用面膜后对最大剂量点的剂量影响在X6和E9分别为0.5%和3%.(3)射出线束对皮肤剂量最大增加量为1.3%.结论 X6和E9的入射线会对皮肤剂量产生较大影响.而X6在使用面膜后无论出射线还是入射线对最大剂量点的剂量影响均不大,可以认为使用面膜不必对开机量进行校正;而E9则有3%的剂量增加,考虑为面膜提升PDD值所致,剂量计算时要将此因素考虑进去.