一种减少瓦里安直线加速器静态调强分野数的方法

目的:当靶区尺寸较大,超过瓦里安加速器MLC开放最大限度时,静态调强的射野会分自动为两个或更多的分野。本研究采用固定铅门技术,减少总的射野数。方法:选取10例鼻咽癌患者分别制定分野技术计划和固定铅门技术计划,评价并对比两种计划靶区及危及器官的剂量学参数、机器跳数(MUs)和治疗时间(T)。结果:两种计划都能满足临床剂量要求,靶区的适形指数差异、均匀指数差异、危及器官剂量差异均没有统计学意义(P>0.05)。与分野技术计划相比,固定铅门技术计划的机器跳数平均较少8%,治疗时间平均减少31%(约3.2min),差异具有统计学意义(P<0.05)。结论:对比两种技术的计划。靶区和危及器官的DVH几乎一致,可以显著减少机器跳数和治疗时间,提高工作效率。     

全脑全脊髓照射技术的改进

目的:介绍全脑全脊髓放射治疗的一种新技术。方法:患者采用仰卧位,在整体定位板上做颈肩和体膜固定,行CT扫描定位,将图像传输治疗计划系统,进行三维重建。按照全脑全脊髓照射的要求勾画靶区,设计治疗计划,调整剂量分布。治疗前行CBCT扫描,进行在线的体位验证。结果:通过计划系统进行剂量计算,可以直观显示靶区的剂量分布并加以调整,计划照射野衔接处没有明显的剂量冷点和热点出现体位验证结果符合临床要求;通过CBCT在线验证,保证位置准确。结论:全脑全脊髓放射治疗采用了仰卧位热塑膜固定,较传统的俯卧位使患者更舒适,治疗过程中体位容易保持,确保治疗的准确;CT模拟定位方法,较传统的模拟机定位简单易行,且定位精确;用计划系统计算剂量分布并进行调整,使靶区剂量分布均匀,避免照射野衔接处剂量分布出现冷、热点。     

MRI与CT模拟定位技术在局部晚期鼻咽癌放射治疗中剂量学对比研究

目的 通过MRI模拟定位技术与CT模拟定位技术在局部晚期鼻咽癌肿瘤靶区和危及器官(OAR)勾画方面的应用对比,探讨两种定位技术在鼻咽癌放射治疗中的剂量学差异。方法 选择蚌埠医学院第一附属医院2022年4月至2023年9月接受鼻咽癌放射治疗的37例患者,其中男性29例,女性8例;年龄29～75岁,平均年龄53.14岁;美国癌症联合委员会(AJCC)分期Ⅱ期24例,Ⅲ期13例。患者在相同体位下行CT模拟定位及MRI模拟定位,在CT定位上通过患者现有影像学资料勾画靶区及OAR,并完成三维适形调强治疗计划;然后进行CT模拟定位及MRI模拟定位融合,再进行靶区勾画及OAR勾画;比较两种计划靶区体积、剂量[近似最大剂量(D_2%)、近似最小剂量(D_98%)、中位剂量(D_50%)和OAR接受的最大点剂量(D_max)]及适形性指数(CI)和均匀性指数(HI)差异。并比较二者OAR的剂量学差异。结果 MRI模拟定位图像上所勾画放疗计划靶区体积小于CT模拟定位(30.54 mm³±18.98 mm<...     

半野技术结合非共面照射技术在乳腺癌胸锁联合照射中的应用

目的：介绍一种乳腺癌适形放疗中新的射野衔接技术,以保证乳腺癌患者放疗时锁骨上区域与胸壁区域靶区剂量均匀衔接,并降低治疗计划设计与实施中的操作复杂度。方法：选取一例乳腺癌胸锁联合照射病人,锁骨上靶区采用半野照射技术,胸壁靶区采用非共面切线野照射技术,使上下两组照射野在射野衔接处相切。使用直线加速器6MV-X射线照射靶区,处方剂量设置为50Gy包绕95％靶区体积,使用治疗计划系统计算三维剂量分布。结果：半野照射技术结合非共面照射技术应用于乳腺癌胸锁联合照射时,在治疗计划系统上显示处方剂量在射野衔接处均匀衔接,50Gy处方剂量等剂量线平滑,剂量线未见明显的凹陷和突出现象,无剂量冷热点出现。结论：半野照射技术联合非共面照射技术用于乳腺癌胸锁联合照射。在TPS上演示显示使用该方法能够使相邻射野剂量均匀衔接,适用于胸壁部分靶区头脚方向长度大于20cm的患者放射治疗需求,且使用方法较传统方法更加简单易行,值得推广,临床实际使用中建议使用验证手段来保障该技术的可靠性。     

三维适型放疗与调强放疗在胸中段食管癌根治性放疗中的 剂量学比较

目的 比较胸中段食管癌三维适型放疗与调强放疗对靶区和危及器官的剂量学影响,探讨两种放射治疗方法在胸中段食管癌根治性放疗中重要器官受保护的优劣,寻找食管癌放射治疗的理想计划模式。方法 15例经病理证实胸中段食管鳞癌患者,经体位固定、CT模拟定位扫描成像传输到治疗计划系统、勾画肿瘤体积、临床靶区体积和危及器官。15例病例均做三维适型和调强计划,60 Gy/30次,评估/优化后应用剂量体积直方图比较两种计划对靶区及危及器官的剂量学影响。结果 在相同靶区、相同剂量模式下,对胸中段食管癌患者的放射治疗中,调强放疗对靶区剂量的分布及对危及器官的保护均优于三维适形放疗。结论 胸中段食管鳞癌,长度4~18 cm放射治疗,三维适型/调强放疗对危及器官剂量学的影响有明显差异。同部位的肿瘤受到相同剂量照射情况下,调强放疗对危及器官的影响较三维适型放疗小,靶区剂量分布均匀度好。     

射束强度受调节的适形放射治疗

射束强度受调节的适形放疗法是一种先进的放射治疗方法，它使用一组强度可独立控制的笔射束，通过旋转或多野静态照射肿瘤靶，使射野内高剂量分布形状在三维方向上与肿瘤靶的形状一致，同时尽可能地减少了靶区周围健康组织的照射剂量，从而大大提高放射治疗的治疗增益比，促进肿瘤的局部控制。本文系统地阐述了强度受调节的适形放疗的优势与治疗计划理论。     

食管癌三维适形放疗和常规放疗比较

目的 对比研究三维适形放疗(3DCRT)和常规模拟机定位放疗两种不同方法在食管癌放射治疗中的优缺点.方法 20例食管癌患者采用3DCRT方法进行治疗,应用同一治疗计划系统,制定适形放疗和常规模拟机定位放疗方案.结果 与常规模拟定位机定位放疗相比,食管癌照射中3DCRT有最好的剂量分布,既可明显提高靶区的剂量,同时能较好地保护正常组织.结论 食管癌的适形放疗技术能降低正常组织的放射损伤和并发症,提高放疗治疗的适形度,改善靶区的剂量分布.     

旋转MLC优化适形放射治疗中的射野适形度

采用多叶准直器（MLC）适形野放疗是临床中常用的技术，但其叶片的有限宽度造成的锯齿形射野轮廓是影响射野适形度的主要原因之一。通过模拟计算，考察了旋转准直器角度对射野适形度的影响，提出用多个旋转MLC野形成复合野以使靶区得到更均匀照射，从而避免靶区上的冷点和危及器官上的热点。结果表明，复合MLC射野不仅可以消除射野的锯齿形边界．明显提高射野的适形情况，同时复合射野后靶区的受照射面积也更均匀，避免了照射冷点的出现。     

用多叶准直器实现适形放射治疗

适形放射疗法是一种先进的放射疗法。它通过旋转照射或静态多射野照射使得高剂量区剂量分布的形状在三维方向上与靶区（病灶）的实际形状一致，而尽可能地降低靶区周围健康组织的照射量，从而大大提高放射治疗的治疗增益比，提高单次照射所能给出的处方剂量，达到更好的治疗效果。本文系统地阐述了用多叶准直器实现适形放疗的理论与技术。     

利用模拟机及挡铅托架进行放疗前的治疗模拟

目的：通过对食管癌实例分析,理清放射治疗的全部过程,重点是利用模拟机模拟病人放疗过程,从中探讨模拟机的模拟过程在三维适形放射治疗中的临床应用价值。方法：以10位4野照射的食管癌病人为例,首先进行常规放疗模拟机的质量保证和质量控制（QA／QC）,本文重点介绍等中心精度的检验和光野射野的一致性;然后利用双螺旋CT机、体位固定装置、三维激光定位系统、常规放疗模拟机及挡铅托架对放疗病人进行体模制作、CT定位、制定治疗计划、制作挡铅及进行模拟验证,分别从寻找射野中心、射野验证、计算深度验证、治疗计划各项参数的可行性验证四个方面进行分析。结果：常规放疗模拟机的各项指标达到QA规定的允许限度内。通过治疗计划显示的各种参数（挡块、楔形等）的调整及修饰后,在常规X线模拟机下对照射野位置及计算深度进行验证可发现：全部患者的计算深度符合临床要求;大部分患者的剂量分布符合临床要求,成功率达90％;射野中心偏移误差最大为3．5mm,最小为0．5mm。在整个治疗过程中,两位患者出现了与床相撞的情况。结论：对放疗患者进行放疗前模拟的过程是三维适形放疗的重要环节,用于验证放疗计划的可行性,保证放疗过程安全有效地进行。     

Varian多叶准直器(MLC)常规测量方法及质量保证

目的:通过建立一套多叶准直器(MLC)常规测量方法,探讨用MLC进行三维适形放射治疗(3-Dimension confor-mal radiation therapy,3D CRT)质量保证(QA)的内容.方法:物理师采用胶片法对Varian 23EX加速器,120叶MLC、Cadplan治疗计划系统进行治疗前、每日、每月、三个月的质量保证项目检测.结果:MLC形成的照射野与灯光野的重合性、叶片位移的精确度、数字化仪的精度、叶片运动的倾斜度、下垂度、照射野中心均在允许范围内,符合临床要求.结论:Varian 120叶MLC性能稳定、可靠.     

Intensity-modulated radiation therapy: overlapping co-axial modulated fields

The Varian multi-leaf collimator has a 14.5 cm leaf extension limit from each carriage. This means the target volumes in the head and neck region are sometimes too wide for standard width-modulated fields to provide adequate dose coverage. A solution is to set up asymmetric co-axial overlapping fields. This protects the MLC carriage while in return the MLC provides modulated dose blending in the field overlap region. Planar dose maps for coincident fields from the Pinnacle radiotherapy treatment planning system are compared with planar dose maps reconstructed from radiographic film and electronic portal images. The film and portal images show small leaf-jaw matchlines at each field overlap border. Linear profiles taken across each image show that the observed leaf-jaw matchlines from the accelerator images are not accounted for by the treatment planning system. Dose difference between film reconstructed electronic portal images and planning system are about 2.5 cGy in a modulated field at d(max). While the magnitude of the dose differences are small improved round end leaf modelling combined with a finer dose calculation grid may minimize the discrepancy between calculated and delivered dose.     

Varian 23EX加速器固定剂量率旋转调强技术的Portal Dosimetry验证

目的:应用Varian公司的Portal Dosimetry系统和ScandiDos公司的Delta4三维半导体阵列对Varian 23EX加速器固定剂量率旋转调强（CDR-VMAT）计划进行验证并对比分析。方法:随机选取10例头颈部肿瘤患者、10例胸部肿瘤患者和10例腹部肿瘤患者,采用RayStation计划系统在Varian 23EX加速器上设计CDR-VMAT。照射野根据肿瘤部位合理设计,射线能量为6 MV X线,每个弧的剂量率和机架转速恒定并由计划系统优化给出。据此分别生成适用23EX自带EPID的Portal Dosimetry验证计划和适用Delta4的验证计划,按照3 mm DTA、3% Dose标准分析其Gamma通过率,并进行配对t检验。结果:10例头颈部肿瘤CDR-VMAT计划Portal Dosimetry验证和Delta4验证的Gamma通过率分别为（97.9±1.1）%和（99.9±0.2）%,P<0.05。10例胸部肿瘤CDR-VMAT计划的Gamma通过率分别为（99.5±0.7）%和（99.7±0.4）%,P=0.09。10例腹部肿瘤CDR-VMAT计划的Gamma通过率分别为（99.5±0.3）%和（99.7±0.4）%,P=0.19。结论:CDR-VMAT技术作为Varian 23EX加速器一种可选的放射治疗技术能够有效提高机器的计划执行效率,配合Varian Portal Dosimetry系统可以方便地对23EX加速器上的CDR-VMAT计划进行验证。通过与Delta4进行比较,对胸部和腹部肿瘤计划,其Gamma通过率均大于95%且无显著差异,对于头颈部肿瘤计划Gamma通过率有差异,但均满足大于95%的要求。     

An experimental investigation into the radiation field offset of a dynamic multileaf collimator

In this study we investigate the characteristics of a rounded leaf end multileaf collimator (MLC) that is used for delivering intensity-modulated radiotherapy (IMRT) with a Varian linear accelerator. The rounded leaf end MLC design results in an offset between the radiation field edge (the physical leaf position) and the light field (the geometric leaf position). We call this the radiation field offset (RFO). The leaf position is calibrated to the leaf tip at the mid-leaf plane. There is an additional offset between the geometric leaf position and the projected leaf tip position that varies as a function of distance from the collimator central axis due to the MLC geometry. We call this the leaf position offset (LPO). There is a lack of consistency in the interpretation and implementation of the RFO and the LPO in the literature. We investigated the RFO and the LPO on Varian's 600 C/D and 21 EX linear accelerators. We used a combination of film and ion chamber measurements of static, segmental MLC (SMLC) and dynamic MLC (DMLC) fields to quantify the leaf offsets across the range of leaf positions. We were able to improve the dosimetry at large off-axis positions with minor adjustments to the vendor's LPO file. The RFO was determined to within 0.1 mm accuracy at the collimator central axis. The measured RFO value depends on whether the method is based on the radiation field edge position or on an integral dose measurement. The integral dose method results in an RFO that is approximately 0.2 mm greater than the radiation field edge method. The difference is due to the MLC penumbra shape. We propose a methodology for measuring and implementing MLC leaf offsets that is suitable for both SMLC and DMLC IMRT. In addition, we propose some definitions that more clearly describe the MLC leaf position for accurate IMRT dosimetry.     

Dosimetric effect of collimating jaws for small multileaf collimated fields

The dosimetric effects from the jaw positioned close to the small field (0.5 x 0.5, 1 x 1, and 2 x 2 cm2) side-edge generated by a single-focused multileaf collimator (MLC) were measured and studied. The measurement is important in intensity modulated radiotherapy (IMRT) because generally the jaw cannot perfectly cover all the leaf-ends in a segment of irregular field. This leads to additional dose contributed by (1) the end surface of the jaw, (2) the leaf-end, and (3) the inter- and intraleaf leakage/transmissions during the dosimetric measurement. Moreover, most of the conventional treatment planning systems ignore these effects in the dose calculation. In this study, measurements were made using a Varian 21 EX linear accelerator with 6 MV photon beam through a MLC containing 120 leaves. Percentage depth dose, beam profile, and output for small fields were measured by varying the jaw at different positions away from the leaf-ends in the field side-edge. Moving the jaw away from the leaf-ends increases the output and penumbra width for the small fields. Such increase is particularly significant when the field size is small (0.5 x 0.5 cm2) and the degree of increase changes quickly when the jaw-end is at about 1-2 cm from the leaf-end. It is suggested that measurements should be carried out in the IMRT commissioning to provide information to physicists in reviewing the treatment planning system's accuracy regarding leaf leakage/transmission and jaw effects.     

Properties of unflattened photon beams shaped by a multileaf collimator

Several studies have shown that removal of the flattening filter from the treatment head of a clinical accelerator increases the dose rate and changes the lateral profile in radiation therapy with photons. However, the multileaf collimator (MLC) used to shape the field was not taken into consideration in these studies. We therefore investigated the effect of the MLC on flattened and unflattened beams. To do this, we performed measurements on a Varian Clinac 21EX and MCNPX Monte Carlo simulations to analyze the physical properties of the photon beam. We compared lateral profiles, depth dose curves, MLC leakages, and total scatter factors for two energies (6 and 18 MV) of MLC-shaped fields and jaw-shaped fields. Our study showed that flattening filter-free beams shaped by a MLC differ from the jaw-shaped beams. Similar differences were also observed for flattened beams. Although both collimating methods produced identical depth dose curves, the penumbra size and the MLC leakage were reduced in the softer, unflattened beam and the total scatter factors showed a smaller field size dependence.     

A method for determining multileaf collimator transmission and scatter for dynamic intensity modulated radiotherapy

The main purpose of this work is to demonstrate a practical means of determining the leaf transmission and scatter characteristics of a multileaf collimator (MLC) pertinent to the commissioning of dynamic intensity modulated radiotherapy, especially for the sweeping window technique. The data are necessary for the conversion of intensity distributions produced by intensity-modulated radiotherapy optimization systems into trajectories of MLC leaves for dynamic delivery. Measurements are described for two, tungsten alloy MLCs: a Mark II 80-leaf MLC on a Varian 2100C accelerator and a Millenium 120-leaf MLC on a Varian 2100EX accelerator. MLC leakage was measured by film for a series of field sizes. Measured MLC leakage was 1.68% for a 10 x 10 cm2 field for both 6 and 18 MV for the 80-leaf MLC. For the 6 MV field, the 1.68% leakage consisted of 1.48% direct transmission and 0.20% leaf scatter. Direct transmission through the 80-leaf MLC, including the rounded leaf tip, was calculated analytically taking into account the detailed leaf geometry and a Monte Carlo-generated energy spectrum of the accelerator. The integrated fluence under the leaf tip was equivalent to an inward shift of 0.06 cm of a hypothetical leaf with a flat, focused tip. Monte Carlo calculations of the dose to phantom beyond a closed 80-leaf MLC showed excellent agreement with the analytic results. The transmission depends on the density of the MLC alloy, which may differ among individual MLCs. Thus, it is important to measure the transmission of any particular MLC. Calculated doses for a series of uniform fields produced by dynamic sweeping windows of various widths agree with measurements within 2%.     

Dose uncertainty due to aperture effects in dynamic fields

Dosimetry of intensity modulated radiation therapy requires accurate modeling of the beamlets that comprise each treatment segment. Planning systems such as Varian Eclipse and Philips Pinnacle recommend measuring dose distributions and output factors for fields as small as possible, generally down to at least 2 x 2 cm2. Conventionally, we perform these measurements for regular fields, defined by the secondary collimators. In practice, it is the multileaf collimation system (MLC) that defines the intensity map and provides dynamic dose modulation in either a moving window or segmented step-and-shoot mode. For this review we have only considered the latter delivery mode. Using this method, we have studied aperture motion effects on the dynamic collimator scatter (S(c)), total scatter (S(c,p)), and phantom scatter (S(p)) factors for various combinations of collimator settings (4 x 4-14 x 40 cm2) and dynamically stepped leaf gaps (0.1 to 1.0 cm) in comparison with those for static field factors. For two different Varian linear accelerators, we found similar results in a systematic dependence of collimator scatter on gap width and collimator setting. As the gap increases from 0.1 to 1.0 cm the dynamic collimator scatter factors converge from a maximum difference of about 30% toward the static field values. At the same time, there is no measurable difference between dynamic field phantom scatter factors and those conventionally obtained for static fields. Second, we evaluated the two planning systems as to how well they account for collimator scatter by attempting to mimic the dynamic apertures used above by planning and measuring dose distributions to several small, cylindrical targets for a similar range of fixed collimator settings. We found that the ratio of measured-to-planned doses as a function of target size were similar to the measured, dynamic S(c) data for the Varian Eclipse planning system, indicating underestimation of dose for targets smaller than 1 cm diameter, but were close to unity for the Philips Pinnacle system, suggestive of the underlying differences in the dose calculation algorithms. We discuss the measurements and results and potential impact on the dosimetry of small clinical targets.     

Development and validation of a BEAMnrc component module for accurate Monte Carlo modelling of the Varian dynamic Millennium multileaf collimator

A new component module (CM), designated DYNVMLC, was developed to fully model the geometry of the Varian Millennium 120 leaf collimator using the BEAMnrc Monte Carlo code. The model includes details such as the leaf driving screw hole, support railing groove and leaf tips. Further modifications also allow sampling of leaf sequence files to simulate the movement of the multileaf collimator (MLC) leaves during an intensity modulated radiation therapy (IMRT) delivery. As an initial validation of the code, the individual leaf geometries were visualized by tracing particles through the component module and recording their position each time a leaf boundary was crossed. A model of the Varian CL21EX linear accelerator 6 MV photon beam incorporating the new CM was built with the BEAMnrc user code. The leaf material density and abutting leaf air gap were chosen to match simulated leaf leakage profiles with film measurements in a solid water phantom. Simulated depth dose and off-axis profiles for a variety of MLC defined static fields agreed to within 2% with ion chamber and diode measurements in a water phantom. Simulated dose distributions for IMRT intensity patterns delivered using both static and dynamic techniques were found to agree with film measurements to within 4%. A comparison of interleaf leakage profiles for the new CM and an equivalent leaf model using the existing VARMLC CM demonstrated that the simplified geometry of VARMLC is not able to accurately predict the details of the MLC leakage for the 120 leaf collimator.     

Multileaf collimator end leaf leakage: implications for wide-field IMRT

The multi-leaf collimator (MLC) of a particular linear accelerator vendor (Millennium MLC, Varian Medical Systems, Palo Alto, CA, USA) has a maximum leaf extension of 14.5 cm. To achieve intensity modulated radiotherapy (IMRT) for fields wider than 14.5 cm all closed leaf pairs are restricted to placement inside the field. Due to the rounded leaf end design of the MLC end leaf leakage will occur in the treatment field. The implementation of direct aperture optimization in the IMRT module of a radiotherapy treatment planning system (Pinnacle, Philips Radiation Oncology Systems, Milpitas, CA) has facilitated the delivery of IMRT fields wider than 14.5 cm. The end leaf leakage of the Millennium MLC has been characterized for 6 MV photons using gafchromic and radiographic film, and the accuracy of the planning system verified. The maximum leakage measured for a single field was 0.39 cGy MU(-1) for a 0 mm leaf gap and 0.51 cGy MU(-1) for a 0.6 mm leaf gap. For a clinical IMRT field leaf end leakage contributed an additional 2-3 Gy over the course of treatment. The planning system underestimated the magnitude of end leaf leakage by 20-40%. The ability to deliver IMRT fields wider than 14.5 cm with the Millennium MLC has improved the efficiency and flexibility of IMRT treatments; however, significant extra dose can be introduced due to end leaf leakage. Caution should be exercised when delivering wide field IMRT as it is not a complete panacea. Any significant occurrences of end leaf leakage predicted by the planning system should be independently verified prior to delivery.