射野大小对全脑调强放疗计划EPID验证结果的影响

目的:利用电子射野影像系统（EPID）对全脑调强放疗计划进行γ测试,寻找计划设计对测试结果的影响,以此分析如何优化全脑调强计划以及推测EPID在剂量验证方面的局限性。方法:选取67例全脑放疗患者,对其放疗计划用加速器自带的EPID进行计划验证,对于容积旋转调强放疗（VMAT）计划统计并分析X方向射野大小与γ（3 mm/3%）通过率的关系,对于调强放疗（IMRT）对比分析大野调强和分野调强计划γ（3 mm/3%）通过率的差异。结果:VMAT计划验证结果发现X方向小于15 cm的射野γ（3 mm/3%）通过率普遍优于大于等于15 cm的射野,利用SPSS软件进行t检验,发现结果具有统计学意义（t=-3.828, P<0.05）;IMRT验证结果发现,X方向大于等于15 cm的射野会包含两个子野,合野验证时其交叠部分γ（3 mm/3%）通过率较差,而采用分野验证时,由于无交叠则通过率普遍较好。结论:全脑放疗VMAT计划将X方向射野控制在15 cm以内可以提升多叶准直器调节能力,并提高EPID验证的γ（3 mm/3%）通过率;EPID原件对低剂量区的响应偏差会导致全脑IMRT大野调强计划两子野交叠处γ（3 mm/3%）通过率较差,改用分野验证可以显著消除这种影响。     

基于EPID采用参数化梯度法测定光子束射野边界

【摘 要】 目的:探究参数化梯度方法（PGM）测量电子射野影像系统（EPID）光子束射野大小的可行性。 方法:PGM通过一个修改的双曲正切函数拟合Profile半影区。瓦里安EDGE机载aS1200采集6 MV和10 MV FF及FFF射束EPID数据,TrueBeam机载aS1000采集6 MV FF射束EPID数据。γ分析1 mm/1%标准量化PGM拟合Profile半影区与EPID测量半影区一致性。比较半高宽方法与PGM测量的FF射束射野大小,比较最大斜率方法与PGM测量的FFF射束射野大小;比较PGM在不同射束能量、不同EPID探测器类型和引入铅门位置误差后测量射野边界的稳定性和扩展性。 结果:半影区PGM拟合与EPID实测数据Pearson相关系数大于0.999,γ值小于0.2。FF射束,半高宽方法测定射野均大于PGM,且随着射野增大而增大,Profile本影去除后,两种方法测量差值显著减小;FFF射束,最大斜率方法与PGM测定射野大小差值在0.1 mm以内。PGM能够稳定测量不同能量、不同模态、不同EPID探测器类型射野边界,能够准确识别铅门1 mm位置变动。 结论:PGM可作为一种鲁棒通用的方法适用于EPID光子束射野质量保障。     

调强放射治疗射野和剂量的验证

目的：为确保调强放射治疗的精确,利用自制和专用设备对每个射野的位置、形状和野内剂量分布进行验证。方法：用自制的位置验证标记球,贴在病人体表的某个固定位置,和病人一起进行CT扫描,设计计划时将此标记球设为位置验证靶区进行射野位置验证。利用加速器自带的射野影像系统（EPID）和治疗计划系统（TPS）的DRR图比对进行射野形状验证。利用Matrixx二维电离室矩阵和OnmiPro软件进行每个射野的剂量验证。结果：射野位置验证在统一调整系统后,误差结果满意。射野形状验证以3mm为标准,调整前的吻合率约为75％。剂量验证通过率大于等于95％的射野占77％。结论：通过81例鼻咽癌调强放疗的实验证明,利用上述三种方法对调强计划进行验证,可以及时纠正误差,确保计划准确执行。     

射野区域的剂量验证研究

目的:实现射野区域剂量分布Gamma（[γ]）通过率的计算,对治疗传输的准确性进行评估。方法:从Oncentra Masterplan治疗计划系统中随机提取6位完全匿名患者的调强放射治疗验证计划,导出DICOM格式的验证计划并利用Matlab软件重建多叶准直器区域和剂量。然后将验证计划移植到MatriXX模体并测量剂量分布。用Matlab代码对验证计划剂量分布和模体测量的绝对剂量分布进行分析。结果:传统方法[γ]通过率受计算区域选择影响较大,而以射野区域作为计算区域则避免了这个问题,两种方法计算得到的[γ]通过率有统计学差异（[P]<0.05）。结论:射野区域的剂量验证避免了[Dn]值对[γ]通过率的影响,而且对射野区域利用剂量面积直方图分析其剂量特性,有利于评估治疗计划系统临床治疗的准确性和指导临床工作。     

基于电子射野影像装置的EDose5.0系统在鼻咽癌VMAT计划三维剂量验证的可行性

目的:分析基于电子射野影像装置(EPID)的EDose5.0系统在鼻咽癌容积旋转调强放疗(VMAT)计划三维剂量验证的可行性。方法:选取在院内接受治疗的15例鼻咽癌患者作为观察对象,应用基于EPID的EDose5.0、Delta4与Arc CHECK三维剂量验证系统对鼻咽癌VMAT计划做验证测量。在不同Gamma(γ)分析标准条件下,对比不同三维验证系统的通过率情况。结果:分析标准为3%/3 mm、最小阈值为10%,鼻咽癌VMAT计划的通过情况较为理想,通过率达到95%之上,能够满足患者治疗中的需求。在标准不断严苛下,验证系统的通过率随之有所降低,两者之间存在负相关关系。分析标准为3%/3 mm、3%/2 mm、2%/2 mm、2%/1 mm时,EDose5.0与Delta4或ArcCHECK对比无显著差异(P0.05),而分析标准为3%/1 mm时,有统计学差异(P0.05)。分析标准为2%/3 mm、1%/3mm、1%/2 mm、1%/1 mm时,EDose5.0对比Delta4有统计学差异(P0.05),但EDose5.0对比Arc CHECK无显著差异(P0.05)。结论:基于EPID的EDose5.0系统在鼻咽癌VMAT计划三维剂量验证中具有可行性,有助于保障验证精准度。     

Machine Performance Check束流均匀性改变对Portal Dosimetry计划剂量验证的影响

目的：探究Machine Performance Check(MPC)系统束流均匀性变化对Portal Dosimetry(PD)计划验证的影响,为临床MPC均匀性的阈值设定和电子影像系统（EPID）的校准频率提供参考。方法：选取本中心EDGE加速器上首次治疗患者26例和10 cm×10 cm方野1例,制定治疗计划和验证计划。在MPC束流均匀性偏差增大的情况下,分别在EPID校准前和校准后执行验证计划,并在计划系统PD模块中分析,统计对比图像剂量和γ通过率。本研究还列出EDGE加速器一年间MPC束流均匀性的结果。结果：MPC 1年的统计结果显示束流均匀性偏差的升高趋势明显并且速度加快,表明EPID存在设备老化现象。EPID校准前后验证计划的图像剂量和γ通过率的对比结果表明不同能量方野计划在影像板中心附近的剂量差异为1%～2%,临床射野计划由于复杂性提高,剂量差异最大可以达到10%。EPID校准后的γ通过率高于校准前。结论：EPID探测器的一致性改变对PD计划剂量验证有一定影响,提示临床MPC均匀性阈值为2%时能够对PD计划剂量验证起到预警作用,EPID应在MPC重新采集基线之前校准,以...     

基于EPID宫颈癌IMRT验证的不同Gamma通过率参数影响分析

目的:使用Varian 非晶硅电子射野影像系统（EPID）对80例宫颈癌术后患者的放疗计划进行Gamma通过率验证,分析不同机架角度、两台同型号加速器间Gamma通过率的差异;探讨3种参数设置对Gamma通过率的影响,为计划验证提供理论依据。方法:对每一患者制定7野均分治疗计划并创建验证计划,在两台相同型号的Varian Unique（1、2）加速器上进行验证并获取验证图像;通过Portal Dosimetry（PD）软件获得不同参数设置（标准剂量差异与距离符合度）下的Gamma通过率,对其进行统计学分析。结果:参数设置分别为PD_Global/PD_Local 1%/1 mm、2%/2 mm、3%/3 mm,剂量阈值10%。（1）当参数为PD_Global（2%/2 mm、1%/1 mm）时,Gan=0°的Gamma通过率优于其他角度;Gan=104°、256°的Gamma通过率低于其他角度（P<0.05）。参数为PD_Local（3%/3 mm、2%/2 mm、1%/1 mm）时,Gan=0°的Gamma通过率低于其他角度（P<0.05）。（2）参数为PD_Global 1%/1 mm、PD_Local 1%/1 mm时,Unique-2的Gamma通过率高于Unique-1（P<0.05）。结论:严格的参数设置能够体现机架角度、加速器性能等对Gamma通过率的影响;针对不同部位的肿瘤需要加入相关的分析条件。为提高放疗的精确性,物理师需要增加对射野影像装置、机架角位移、多叶准直器到位精度等设备参数的检测频率,并通过大量数据的累积与临床相结合,制定更严格的Gamma通过率参数与限值。     

用蒙特卡罗模拟评估小野条件下肺介质中AAA算法的精度

目的：用蒙特卡罗模拟评估放射治疗剂量计算使用的各向异性分析算法（Anisotropic Analytical Algorithm,AAA）在小野条件下肺介质中的计算精度。材料与方法：建立一包含肺介质的水模体,分别用AAA算法、笔形束卷积算法（Pencil Beam Convolution,PBC算法）（作为对比）和蒙特卡罗（Monte Carlo,MC）模拟计算2cm×2cm到8cm×8cm射野条件下该模体中的深度剂量和离轴比,并以MC模拟为标准比较深度剂量。用一维伽马分析对离轴比进行分析。结果：AAA算法在2cmx2cm射野肺介质区域高估了深度剂量,其它情况均低估了深度剂量,剂量偏差范围为-0．24％-2．66％．PBC算法在肺介质区域高估了深度剂量,剂量偏差的范围为1．18％～14．55％。AAA算法计算的离轴比和MC模拟,在射野剂量平坦区相对内收,在剂量跌落区向两侧发散,但AAA算法略高估了射野边缘的剂量,一维伽马分析（与MC相比）通过率为100％（3mm／3％）。PBC算法在射野剂量平坦区相对发散,而在剂量跌落区向两侧内收。一维伽马分析通过率范围为51％～88％。结论：在肺介质中,AAA剂量计算的结果与MC模拟的一致性较好,与PBC算法相比,剂量计算的精度较高。     

基于EDose软件电子射野影像系统的调强剂量验证

目的:探讨电子射野影像系统(EPID)用于调强放射治疗三维剂量验证的可行性。方法:分别使用Varian公司的Trilogy加速器自带的EPID及EDose软件和美国Sun Nuclear公司的Mapcheck剂量验证系统及配套模体对10例调强放射治疗的患者进行剂量验证,记录并比较分析两种系统的绝对剂量和相对剂量γ通过率的相关性。结果:采用γ(3%/3mm)标准时,相对剂量EPID和Mapcheck验证的γ通过率分别为(98.51%±1.10%)、(98.73%±0.69%);绝对剂量EPID和Mapcheck验证的γ通过率分别为(96.50%±3.33%)、(97.64%±1.51%),两者均无统计学意义(P0.05)。其它标准的γ通过率有统计学意义。结论:EPID可以作为调强三维剂量验证的工具,比Mapcheck更方便快捷。     

算法差异在Compass调强计划验证中的作用

目的:用IBA Compass系统对Varian Eclipse计划系统各向异性解析算法(AAA)计算的肺癌和直肠癌计划进行验证,研究差异原因并进行分类分析。方法:分别选取肺癌和直肠癌术前放疗患者各10例,用Compass系统在加速器实测验证,将Eclipse AAA计算的TPS Dose、Compass卷积/超分割算法(CCC)再计算的Compute Dose以及Compass通过实测并基于CCC算法重建的Reconstructed Dose进行两两对比(AAA/CR、CC/CR、AAA/CC),比较分析计划最大点剂量的10%生成的区域的Gamma结果和剂量体积直方图(DVH)结果。结果:在3 mm/3%/Global标准下,直肠癌术前计划:AAA/CRγ通过率为(97.37±2.41)%,CC/CRγ通过率为(97.88±2.21)%,AAA/CCγ通过率为(99.69±0.15)%,AAA/CRγ通过率与CC/CRγ通过率的差异无统计学意义(P=0.598)。肺癌计划:AAA/CRγ通过率为(92.09±2.79)%,CC/CRγ通过率为(96.17±2.78)%,AAA/CCγ通过率为(98.96±1.06)%,AAA/CRγ通过率与CC/CRγ通过率的差异具有显著统计学意义(P=0.005)。结论:用Compass验证AAA算法计划,在肺癌病例中AAA与CCC算法的差异是影响计划通过率的主要原因,在直肠癌计划中AAA与CCC算法的差异影响相对较低,通过率更多受到MLC到位精度、机架旋转精度、剂量准确度等执行不确定性影响。     

各向异性分析算法和光子笔形束卷积算法在食管癌放射治疗中的剂量学比较

目的比较食管癌调强放射治疗各向异性分析算法（AAA）与光子笔形束卷积（PBC）算法的剂量学差异。方法选取9例食管癌患者,其中男性6例,女性3例;年龄54-68岁,平均年龄61岁。用瓦里安Eclipse 8.6治疗计划系统设计5野均分逆向调强计划,分别用AAA和PBC算法模型计算并利用COMPASS进行剂量验证。利用剂量体积直方图比较靶区、肺、心脏和脊髓照射剂量和体积。数据应用SPSS15.0进行配对t检验分析。结果大体肿瘤区（GTV）的均匀性指数（HI）、适合度指数（CI）、Dmean及计划靶区（PTV）的HI,AAA结果均优于PBC算法,差异均有统计学意义（P〈0.05）。AAA双肺各指标差值为-0.02%～-1.87%,即低估了肺2%以内的受量。PBC算法双肺各指标差值为-3.95%～1.05%,低剂量区（V5～15）低估了肺4%以内的受量,高剂量区（V20～30）则稍高估。对于脊髓,AAA和PBC算法分别高估了1.57%、4.49%。两种算法都低估了心脏的受量,但AAA相对准确。结论食管癌放射治疗中采用AAA优于PBC算法。     

各向异性解析算法与先进外照射光子剂量算法在肺癌VMAT计划中的剂量学差异

目的:比较先进外照射光子剂量算法（AXB）和各向异性解析算法（AAA）在肺癌VMAT计划中的剂量学差异。方法:随机选取20例肺癌患者,CT扫描传输图像后勾画靶区及危及器官,采用两弧设计VMAT放疗计划,比较两种算法靶区的剂量分布,肺、心脏和脊髓的受照量。结果:PGTV:最大剂量AXB算法低于AAA算法（P<0.05）,最小剂量无统计学意义（P>0.05）,平均剂量AXB算法低于AAA算法（P<0.05）;PTV:最大剂量和最小剂量无统计学意义（P>0.05）,平均剂量AXB算法低于AAA算法（P<0.05）;CI:AXB算法优于AAA算法（P<0.05）;HI:AXB算法优于AAA算法（P<0.05）;脊髓:最大剂量AXB算法低于AAA算法（P<0.05）;心脏:V30、V40、Dmean AXB算法均低于AAA算法（P<0.05）;肺:V5、V20、Dmean AXB算法均低于AAA算法（P<0.05）。结论:两种算法均满足临床要求,但与AAA算法相比,AXB算法更精确,特别是针对肺组织这种低密度区域。     

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。     

The accuracy of dose calculations by anisotropic analytical algorithms for stereotactic radiotherapy in nasopharyngeal carcinoma

Nasopharyngeal tumors are commonly treated with intensity-modulated radiotherapy techniques. For photon dose calculations, problems related to loss of lateral electronic equilibrium exist when small fields are used. The anisotropic analytical algorithm (AAA) implemented in Varian Eclipse was developed to replace the pencil beam convolution (PBC) algorithm for more accurate dose prediction in an inhomogeneous medium. The purpose of this study was to investigate the accuracy of the AAA for predicting interface doses for intensity-modulated stereotactic radiotherapy boost of nasopharyngeal tumors. The central axis depth dose data and dose profiles of phantoms with rectangular air cavities for small fields were measured using a 6 MV beam. In addition, the air-tissue interface doses from six different intensity-modulated stereotactic radiotherapy plans were measured in an anthropomorphic phantom. The nasopharyngeal region of the phantom was especially modified to simulate the air cavities of a typical patient. The measured data were compared to the data calculated by both the AAA and the PBC algorithm. When using single small fields in rectangular air cavity phantoms, both AAA and PBC overestimated the central axis dose at and beyond the first few millimeters of the air-water interface. Although the AAA performs better than the PBC algorithm, its calculated interface dose could still be more than three times that of the measured dose when a 2 × 2 cm(2) field was used. Testing of the algorithms using the anthropomorphic phantom showed that the maximum overestimation by the PBC algorithm was 20.7%, while that by the AAA was 8.3%. When multiple fields were used in a patient geometry, the dose prediction errors of the AAA would be substantially reduced compared with those from a single field. However, overestimation of more than 3% could still be found at some points at the air-tissue interface.     

Clinical experience with EPID dosimetry for prostate IMRT pre-treatment dose verification

The aim of this study was to demonstrate how dosimetry with an amorphous silicon electronic portal imaging device (a-Si EPID) replaced film and ionization chamber measurements for routine pre-treatment dosimetry in our clinic. Furthermore, we described how EPID dosimetry was used to solve a clinical problem. IMRT prostate plans were delivered to a homogeneous slab phantom. EPID transit images were acquired for each segment. A previously developed in-house back-projection algorithm was used to reconstruct the dose distribution in the phantom mid-plane (intersecting the isocenter). Segment dose images were summed to obtain an EPID mid-plane dose image for each field. Fields were compared using profiles and in two dimensions with the y evaluation (criteria: 3%/3 mm). To quantify results, the average gamma (gamma avg), maximum gamma (gamma max), and the percentage of points with gamma < 1(P gamma < 1) were calculated within the 20% isodose line of each field. For 10 patient plans, all fields were measured with EPID and film at gantry set to 0 degrees. The film was located in the phantom coronal mid-plane (10 cm depth), and compared with the back-projected EPID mid-plane absolute dose. EPID and film measurements agreed well for all 50 fields, with (gamma avg) =0.16, (gamma max)=1.00, and (P gamma < 1)= 100%. Based on these results, film measurements were discontinued for verification of prostate IMRT plans. For 20 patient plans, the dose distribution was re-calculated with the phantom CT scan and delivered to the phantom with the original gantry angles. The planned isocenter dose (plan(iso)) was verified with the EPID (EPID(iso)) and an ionization chamber (IC(iso)). The average ratio, (EPID(iso)/IC(iso)), was 1.00 (0.01 SD). Both measurements were systematically lower than planned, with (EPID(iso)/plan(iso)) and (IC(iso)/plan(iso))=0.99 (0.01 SD). EPID mid-plane dose images for each field were also compared with the corresponding plane derived from the three dimensional (3D) dose grid calculated with the phantom CT scan. Comparisons of 100 fields yielded (gamma avg)=0.39, gamma max=2.52, and (P gamma < 1)=98.7%. Seven plans revealed under-dosage in individual fields ranging from 5% to 16%, occurring at small regions of overlapping segments or along the junction of abutting segments (tongue-and-groove side). Test fields were designed to simulate errors and gave similar results. The agreement was improved after adjusting an incorrectly set tongue-and-groove width parameter in the treatment planning system (TPS), reducing (gamma max) from 2.19 to 0.80 for the test field. Mid-plane dose distributions determined with the EPID were consistent with film measurements in a slab phantom for all IMRT fields. Isocenter doses of the total plan measured with an EPID and an ionization chamber also agreed. The EPID can therefore replace these dosimetry devices for field-by-field and isocenter IMRT pre-treatment verification. Systematic errors were detected using EPID dosimetry, resulting in the adjustment of a TPS parameter and alteration of two clinical patient plans. One set of EPID measurements (i.e., one open and transit image acquired for each segment of the plan) is sufficient to check each IMRT plan field-by-field and at the isocenter, making it a useful, efficient, and accurate dosimetric tool.     

Collapsed cone convolution and analytical anisotropic algorithm dose calculations compared to VMC++ Monte Carlo simulations in clinical cases

The purpose of this work was to study and quantify the differences in dose distributions computed with some of the newest dose calculation algorithms available in commercial planning systems. The study was done for clinical cases originally calculated with pencil beam convolution (PBC) where large density inhomogeneities were present. Three other dose algorithms were used: a pencil beam like algorithm, the anisotropic analytic algorithm (AAA), a convolution superposition algorithm, collapsed cone convolution (CCC), and a Monte Carlo program, voxel Monte Carlo (VMC++). The dose calculation algorithms were compared under static field irradiations at 6 MV and 15 MV using multileaf collimators and hard wedges where necessary. Five clinical cases were studied: three lung and two breast cases. We found that, in terms of accuracy, the CCC algorithm performed better overall than AAA compared to VMC++, but AAA remains an attractive option for routine use in the clinic due to its short computation times. Dose differences between the different algorithms and VMC++ for the median value of the planning target volume (PTV) were typically 0.4% (range: 0.0 to 1.4%) in the lung and -1.3% (range: -2.1 to -0.6%) in the breast for the few cases we analysed. As expected, PTV coverage and dose homogeneity turned out to be more critical in the lung than in the breast cases with respect to the accuracy of the dose calculation. This was observed in the dose volume histograms obtained from the Monte Carlo simulations.