呼吸运动对调强放疗影响的实验研究

目的：评价静态调强放疗治疗肺癌等运动幅度较大肿瘤的可行性。方法：应用自行研制的运动体模系统模拟呼吸运动，测量不同运动幅度及不同运动方向对基于多叶光栅的静态调强放疗射束半影、剂量分布及绝对剂量的影响。结果：靶区运动明显增加了射野在运动方向的半影，导致了低剂量区面积增大及高剂量区不确定性的增加，但70％～90％的等剂量线变化不显著。虽然不同情况下各测量点的剂量有不同程度的变化，但若将运动等不确定性因素考虑在内，多次测量后总体变化幅度均在允许的范围之内。结论：靶区运动加宽了射束的半影，但在适当补偿运动等影响靶区确定的因素后，应用静态调强放疗治疗周期性运动的肿瘤是可行的。     

基于MatriXX系统研究呼吸运动对靶区受照剂量分布影响

目的 探讨呼吸运动对三维适形放疗(3DCRT)和调强放疗(IMRT)靶区受照剂量分布影响.方法 用固体水自制剂量测量体模和模拟呼吸运动的平台,与二维空气电离室矩阵MamXX系统配合,分别测量体模在静态和周期运动状态(幅度为±1 cm,周期3.5 s)下进行多角度3DCRT和IMRT的二维剂量分布,然后用MatriXX系统软件对两种不同状态下所测剂量分布进行对比分析.结果 对3DCRT在运动方向上所测剂量分布半影较静态时增加6～9 mm,高剂量区域向内收缩约5mm,低剂量区域向外扩张约5 mm,但50%等剂量曲线范围及中心区域剂量未见明显改变;IMRT各子野单独照射且以测量平面最大剂量为归一剂量时,运动和静止状态下所测剂量差异介于-56.4%～56.1%,其平均值约±27%;IMRT计划所有子野叠加照射时,两种运动状态下在射野中绝大部分区域的剂量差异<±3%,其剂量偏差主要出现在射野边缘,最大约为±15%,这与3DCRT照射的特点相似.结论 无论是3DCRT还是IMRT多次分割照射后,周期运动靶区中心区域受照剂量与静态靶区相近,但高剂量区域向内收缩,低剂量区域向外扩张.     

调强放射治疗的体位固定和摆位

调强放疗(IMRT)它能够优化配置射野内各射束的权重，使各剂量区剂量分布的形状在三维方向上与靶区的实际形状一致。计划靶区(PTV)内的剂量分布更均匀。如果需要，在PTV边缘可以同时形成非常陡的剂量梯度。这意味着靶区周围的正常组织受高剂量的辐射的体积将显著减少，从而可以较大幅度的增加肿瘤剂量或减少正常组织的受量提高肿瘤控制率，降低正常组织并发症的发生率。我院自2003年开展调强放射治疗以来，已收治了145例患者，在调强放射治疗的体位固定和摆位过程中的注意事项及体会介绍如下。     

调强放射治疗的体位固定和摆位

调强放疗(IMRT)它能够优化配置射野内各射束的权重,使各剂量区剂量分布的形状在三维方向上与靶区的实际形状一致。计划靶区(PTV)内的剂量分布更均匀。如果需要,在PTV边缘可以同时形成非常陡的剂量梯度。这意味着靶区周围的正常组织受高剂量的辐射的体积将显著减少,从而可以较大幅度的增加肿瘤剂量或减少正常组织的受量提高肿瘤控制率,降低正常组织并发症的发生率。我院自2003年开展调强放射治疗以来,已收治了145例患者,在调强放射治疗的体位固定和摆位过程中的注意事项及体会介绍如下。1临床资料145例患者中男性114例,女性31例;年龄12~8…     

鼻咽癌螺旋断层放疗与常规加速器调强放疗的剂量学比较

目的 通过比较鼻咽癌螺旋断层放疗与常规直线加速器静态调强治疗计划,研究其剂量学特性.方法 选10例鼻咽癌患者的CT图像,统一勾画靶区及正常器官后,分别传输至螺旋断层放疗、常规调强放疗逆向调强计划系统.统一给予肿瘤靶区(pGTV、PTVnd)处方剂量70 Gy分33次,亚临床病灶区(PTV1)60 Gy分33次,预防照射区(PTV2)54 Gy分33次.正常器官限制体积与剂量为腮腺V35＜50%,脑干＜54 Gy,脊髓＜45 Gy,晶体＜9 Gy等.对两组数据进行配对t检验.结果 两组计划均有较好靶区处方剂量分布,但螺旋断层放疗组的均匀性好于常规调强放疗组;PTV1平均剂量(63.84 Gy)也显著低于常规调强放疗组(70.30 Gy);腮腺平均剂量较常规常规调强放疗组低5.3Gy,V30及V35显著低于常规调强放疗组;喉-气管-食管的最大剂量也较常规调强放疗组明显降低.结论 在鼻咽癌调强放疗中,螺旋断层放疗较常规直线加速器静态调强放疗有更好的剂量均匀性及更陡峭的剂量梯度,并可更好地保护正常器官.     

基于非小细胞肺癌碳离子点扫描治疗的不同优化策略研究

目的 通过设计4种碳离子点扫描优化策略,对非小细胞肺癌(NSCLC)的靶区剂量覆盖和危及器官(OARs) 受量变化来评估各策略。方法 10例NSCLC粒子治疗患者,于治疗期间采集多组四维CT (4DCT)用于剂量评估。4种优化策略为单纯调强优化(IMCT-NoAS)、调强优化结合肿瘤内靶区(IGTV)组织密度设定(IMCT-ASM)、单纯单射野优化(SBO-NoAS)、单射野优化结合靶区组织密度设定(SBO-ASM)。初始计划在复查4DCT数据上重新计算后与初始计划做剂量比较。结果 初始计划在复查CT数据上重新计算后各策略间靶区覆盖相近,仅IMCT-NoAS有较大剂量分布差异。而OARs剂量相对于初始计划患侧肺V20生物有效剂量(RBE)最大增加约2.0 Gy;IGTV组织密度设定计划,心脏V30最大增加RBE约1.0 Gy,而IGTV未设定的计划则最大降低RBE约0.2 Gy;脊髓的RBE最大值约有2.5 Gy差异。结论 碳离子治疗对射束路径上的肿瘤内运动变化敏感。当肿瘤在头脚方向的运动幅度>8 mm时,SBO-ASM 策略有较好的靶区覆盖,但潜在导致剂量分布过冲到比初始计划剂量分布更深的位置。     

多叶准直器角度因素对调强放疗计划实施效率的影响

目的 探讨调强放疗计划优化时多叶准直器(MLC)角度因素对优化结果中子野数(滑窗模式下为控制点数)和机器跳数影响,以及由此对调强放疗实施效率的影响。方法 选择10例拟行调强放疗的靶区形状为长条状的患者CT图像,在MLC运行方向与靶区长轴垂直(横向)和平行(纵向)方向分别以静态子野调强方式和滑窗调强方式设计计划并进行优化,在保证靶区和危及器官受量相同情况下,分别比较静态子野调强模式和滑窗调强模式下两种准直器角度时计划子野数或控制点数和机器跳数差别。结果 MLC纵向方式较横向方式静态子野数平均增加52.8%,滑窗调强控制点数增加58.2%,机器跳数平均增加幅度分别为49.6%和61.9%,子野数或控制点数和机器跳数均不同(P=0.000)。结论 在MLC调强放疗计划优化中选择MLC运行方向垂直于靶区长轴,在不影响靶区和危及器官受量情况下,可明显减少子野数或控制点数和机器跳数、缩短治疗时间、提高治疗效率,具有一定的临床实用价值。     

呼吸运动幅度对静态IMRT剂量分布的影响研究

目的 研究呼吸运动幅度对静态IMRT剂量分布的影响,为受其影响的剂量修正提供指导。方法 采用QUASAR程控呼吸运动仪带动二维矩阵模拟人体上下方向呼吸运动,采集不同呼吸运动幅度等中心层面剂量分布。通过Verisoft软件及绝对剂量分析,分析采集数据与计划剂量分布、绝对剂量百分误差、射野通过率。结果 呼吸运动对靶区内剂量分布影响较小,主要使运动方向边缘靶区外剂量偏高;当呼吸运动幅度<6 mm时γ通过率能满足临床剂量验证需求,>8 mm时随着呼吸幅度的增加γ通过率变小,不能满足临床需求。结论 呼吸运动对静态IMRT技术的影响主要是模糊效应,可通过适当补偿方法确定静态IMRT周期性呼吸运动肿瘤的可行性。呼吸运动方向靶区边缘正常组织实际受量高于计划评价,制定放疗计划时应尽可能降低周围正常组织受量。对呼吸运动幅度较大者,应采取措施减小呼吸幅度提高靶区受照。     

呼吸运动对肺癌动态调强放疗剂量分布的影响

目的：研究动态调强放疗中呼吸运动对肺癌患者靶区剂量分布的影响。方法：使用大孔径CT获得30例肺癌患者四维CT（4D-CT）10个时相的CT图像,在计划系统上利用4D-CT确定肿瘤运动范围,并将整个肿瘤运动范围勾画为GTV。将检测设备放置在自行研制的呼吸运动模拟平台上,对利用4D-CT得到的带有呼吸运动信息的GTV决定的PTV进行治疗,测量每个计划的绝对剂量误差和照射野相对剂量分布误差,分析测量结果。结果：所有计划单次治疗等中心点绝对剂量误差均在允许范围之内。运动范围≤3mm的肿瘤照射野单次治疗的剂量分布误差均在允许范围之内,但运动范围〉3mm的肿瘤照射野的单次治疗剂量分布误差均超过允许范围,尤其是射野边沿。经20-30次治疗后,运动范围≤5mm的肿瘤照射野的剂量分布的通过率均〉95%,但运动范围〉5mm的肿瘤照射野的剂量分布误差均超过允许范围。结论：对于肺部肿瘤进行动态调强放疗时,虽然靶区等中心处绝对剂量误差〈5%,但整个靶区内的剂量分布与计划剂量分布有明显区别,分次治疗可以减小剂量分布误差,但对运动范围〉5mm的肿瘤无效,即通过外放边界不能使肺部呼吸运动范围〉5mm的肿瘤靶区获得预设的剂量分布,肺部调强放疗最好使用呼吸门控技术以减小剂量分布误差。     

同期整合推量调强放射治疗在肿瘤中的研究进展

摘 要：放射治疗在肿瘤中占重要地位,随着放疗技术的飞速发展,目前调强放疗（intensity-modulated radiotherapy,IMRT）已经广泛应用于肿瘤中,但在某些肿瘤中的疗效仍不佳。理论上增加放疗剂量可以提高肿瘤的局部控制率和延长患者的总生存期,但同时会增加放疗毒性,且延长总的治疗时间。同期整合推量调强放射治疗（simultaneous integrated boost intensity-modulated radiotherapy,SIB-IMRT)技术可以在同一次治疗中将不同剂量给予不同靶区而不延长总治疗时间,显著提高肿瘤靶区的生物有效剂量且尽量避开危及器官。本文就SIB-IMRT在头颈部、胸部和盆腔肿瘤中的安全性及疗效作一综述。     

不同机架角时多叶准直器叶片对不同调强放疗剂量影响

目的 研究加速器多叶准直器角度为0°和不同机架角时多叶准直器叶片对不同调强放疗剂量的影响.方法 用30 cm×30 cm×3 cm固体水模体预选静态调强和动态调强中大小合适的30个单方向野和机架角为0°、45°、90°、270°、315°,用Mapcheck二维半导体矩阵测量和其剂量分析系统的γ分析方法(3%/3 mm、5%/3 mm)对相应通过率进行定量分析.以治疗靶区由小到大预选30例患者的静态调强和动态调强计划用上述同样方法测量和分析.结果 加速器多叶准直器角度为0°和机架角分别为0°、45°、90°、270°、315°时静态调强和动态调强30个单方向野实测的3%/3 mm平均通过率分别为97.71%和96.25%(t=1.70,P=0.389)、96.34%和93.72%(t=2.95,P=0.002)、96.65%和92.98%(t=2.87,P=0.005)、95.87%和93.15%(t=2.71,P=0.006)、96.09%和93.51%(t=2.89,P=0.004),5%/3 mm的平均通过率也无差别,分别为99.31%～99.73%和98.89～99.68%(t=0.57～1.90,P=0.913～0.725);30例患者计划的3%/3 mm平均通过率分别为96.11%～96.76%和94.88～95.78%(t=1.02～1.61,P=0.317～0.235).结论 当加速器多叶准直器角度为0°和不同机架角度时多叶准直器叶片对调强放疗剂量相比0°时确有影响,但其面剂量分布误差都在可接受的5%内.

Abstract：

Objective To investigate the impact of accelerator′s multi-leaf collimator (MLC) on the radiotherapy dose with different gantry angles.Methods Measured with Mapcheck 2D diode array and 30 cm×30 cm×3 cm solid water, Pre-selecting the 30 appropriate single fields and 0°,45°,90°,270°,315° gantry angles of static and dynamic intensity modulated radiation therapy (IMRT), quantification analysis of the passing rate with MapCheck γ(3%/3 mm) and (5%/3 mm) analysis methods, and the same method to 30 examples static and dynamic IMRT plans.Results When the accelerator collimator angle is 0°,the 30 appropriate single fields′ passing rate of between 0°gantry angle and 45°,90°,270°,315°gantry angles of static and dynamic IMRT accordingly is 97.71% and 96.25%(t=1.70, P=0.389), 96.34% and 93.72%(t=2.95, P=0.002), 96.65% and 92.98%(t=2.87, P=0.005), 95.87% and 93.15%(t=2.71, P=0.006), 96.09% and 93.51%(t=2.89, P=0.004) with MapCheck γ(3%/3 mm) analysis methods, however, the passing rate also does not have the difference, respectively is 99.31%-99.73% and 98.89-99.68%(t=0.57-1.90, P=0.913-0.725) with MapCheck γ(5%/3 mm) analysis methods;the passing rate of 30 examples static and dynamic IMRT plans accordingly is 96.11%-96.76% and 94.88%-95.78%(t=1.02-1.61, P=0.317-0.235).Conclusions When the accelerator collimator angle is 0°, at different gantry angles, MLC leaves due to gravity, friction, inertia, etc caused by errors in place, the physical penumbra and leakage radiation will indeed affect the IMRT dose, however, the deviation of dose distribution is within acceptable 5%.     

Synchronizing dynamic multileaf collimators for producing two-dimensional intensity-modulated fields with minimum beam delivery time

Purpose: Leaf motion synchronization of dynamic multileaf collimators (DMLC) for intensity-modulated radiotherapy (IMRT) is important in improving dose distribution and reducing “tongue-and-groove” effects for a prescribed intensity profile. Leaf synchronization could also be used in transforming a one-dimensional leaf-setting algorithm into a two-dimensional leaf-setting algorithm. In this work, we aim to develop a generalized leaf synchronization method for delivering IMRT with the minimized beam delivery time and the optimized subfield variations for a leaf-setting sequence.

Methods and Materials: With the leaf synchronization procedure, all active MLC leaf pairs start and finish off a leaf sequence simultaneously. In this work, the MLC leaf pairs were synchronized under the condition that the resulting leaf sequence produces the desired intensity profile with the minimum beam delivery time. The parameter of the leaf synchronization function was determined through the least-square minimization of the area variations of all subfields within a leaf sequence. The leaf synchronization and optimization procedure were applied and analyzed for clinical relevant intensity profiles for treating the head-and-neck cancer patients using IMRT.

Results: The total monitor units and the optimized beam delivery time of generating a two-dimensional intensity profile was proven through this work to be the global minimum of all leaf-setting sequences including the unsynchronized leaf-setting sequences. The optimized parameter for subfield variations of the synchronized leaf trajectories was found to be dependent on individual intensity profiles. For all our studied cases, the unsynchronized leaf trajectories always have significantly larger subfield variations than the synchronized leaf trajectories.

Conclusion: It is important and also feasible to synchronize and optimize dynamic MLC leaf motions while still keeping the total beam delivery time minimum for delivering arbitrary two-dimensional intensity-modulated fields.     

Impact of IMRT and leaf width on stereotactic body radiotherapy of liver and lung lesions

PURPOSE: The present study explored the impact of intensity-modulated radiotherapy (IMRT) on stereotactic body RT (SBRT) of liver and lung lesions. Additionally, because target dose conformity can be affected by the leaf width of a multileaf collimator (MLC), especially for small targets and stereotactic applications, the use of a micro-MLC on "uniform intensity" conformal and intensity-modulated SBRT was evaluated. METHODS AND MATERIALS: The present study included 10 patients treated previously with SBRT in our institution (seven lung and three liver lesions). All patients were treated with 3 x 12 Gy prescribed to the 65% isodose level. The actual MLC-based conformal treatment plan served as the standard for additional comparison. In total, seven alternative treatment plans were made for each patient: a standard (actual) plan and an IMRT plan, both calculated with Helax TMS (Nucletron) using a pencil beam model; and a recalculated standard and a recalculated IMRT plan on Helax TMS using a point dose kernel approach. These four treatment plans were based on a standard MLC with 1-cm leaf width. Additionally, the following micro-MLC (central leaf width 3 mm)-based treatment plans were calculated with the BrainSCAN (BrainLAB) system: standard, IMRT, and dynamic arc treatments. For each treatment plan, various target parameters (conformity, coverage, mean, maximal, and minimal target dose, equivalent uniform doses, and dose-volume histogram), as well as organs at risk parameters (3 Gy and 6 Gy volume, mean dose, dose-volume histogram) were evaluated. Finally, treatment efficiency was estimated from monitor units and the number of segments for IMRT solutions. RESULTS: For both treatment planning systems, no significant difference could be observed in terms of target conformity between the standard and IMRT dose distributions. All dose distributions obtained with the micro-MLC showed significantly better conformity values compared with the standard and IMRT plans using a regular MLC. Dynamic arc plans were characterized by the steepest dose gradient and thus the smallest V(6 Gy) values, which were on average 7% smaller than the standard plans and 20% lower than the IMRT plans. Although the Helax TMS IMRT plans show about 18% more monitor units than the standard plan, BrainSCAN IMRT plans require approximately twice the number of monitor units relative to the standard plan. All treatment plans optimized with a pencil beam model but recalculated with a superposition method showed significant qualitative, as well as quantitative, differences, especially with respect to conformity and the dose to organs at risk. CONCLUSION: Standard conformal treatment techniques for SBRT could not be improved with inversely planned IMRT approaches. Dose calculation algorithms applied in optimization modules for IMRT applications in the thoracic region need to be based on the most accurate dose calculation algorithms, especially when using higher energy photon beams.     

MLC叶片宽度对IMRT计划的影响

目的:探讨不同多叶准直器(multileaf collimator,MLC)叶片宽度对调强放疗(intensity modulated radiotherapy,IMRT)治疗计划的影响。方法: 用ADAC Pinnacle 3型计划系统,对实施IMRT 的11 例鼻咽癌患者,分别用叶片等中心宽度5 mm 和10mm的MLC制定放疗计划,依照剂量体积直方图(dose volume histogram, DVH)对靶区剂量进行综合分析评价,并比较适形指数(radiation conformal index, CI)和剂量均匀指数(homogeneity index,HI)。结果:两种治疗计划的靶区剂量配对t检验显示,靶区和腮腺之间差异有统计学意义,P<0 .05(P值分别为0 .036、0. 002 和0. 001);脑干及脊髓之间差异无统计学意义,P>0 .05(P值分别为0 327和0 545)。5 mm MLC 计划的靶区平均剂量略高于10 mm MLC计划,而两侧腮腺、脑干、脊髓的剂量降低。5 mm MLC计划的CI值明显高于10 mm计划的CI值,t= 9 .779,P= 0 .000。两种计划的HI 值差异无统计学意义,t= 1 257,P= 0 .237。结论:5 mm MLC与10 mm MLC比较,前者适形度好,靶区剂量更均匀,更适合于形状不规则而且邻近危险器官的病灶IMRT。     

比较两种CT模拟定位方法在调强放疗中的误差影响

目的 比较调强放疗中CT模拟定位最终等中心标记法和参考点标记法的误差。方法2009-2012年间327例头颈部肿瘤调强放疗患者使用Philips BrillianceCT Big Bore扫描机及Philips Tumor LOC模拟定位工作站进行定位,其中最终等中心标记法、参考点标记法定位患者分别为208、119例。在瓦里安Eclipse治疗计划系统进行勾画靶区和设计治疗计划。治疗前使用瓦里安EX 直线加速器的机载影像系统千伏级锥形束CT扫描和配准,得出左右、上下、前后方向误差后进行两组比较并成组t检验。最后对5例鼻咽癌患者通过治疗计划系统测量等中心在3个方向移动后对危及器官剂量的影响。结果 最终等中心标记法组3个方向平均误差均小于参考点标记法组(P=0.02、0.01、0.03)。等中心在3个方向上移动后的剂量比较结果显示,靶区受量降低的同时靶区周围正常组织受量明显提高,前后方向误差对脊髓和脑干影响最大。结论 CT模拟定位最终等中心标记法的误差优于参考点标记法,等中心移动的较小误差可引起危及器官较大的受量变化。     

Differential dosing of prostate and seminal vesicles using dynamic multileaf collimation

Purpose: We have investigated the potential of applying different doses to the prostate (PTV2) and prostate/seminal vesicles (PTV1) using multileaf collimation (MLC) for intensity modulated radiation therapy (IMRT). Current dose-escalation studies call for treatment of the PTV1 to 54 Gy in 27 fractions followed by 20 Gy minimum to the PTV2. A daily minimum PTV dose of 2 Gy using a 7-field technique (4 obliques, opposed laterals, and an ant-post field) is delivered. This requires monitor unit calculations, paper and electronic chart entry, and quality assurance for a total of 14 fields. The goal of MLC IMRT is to improve efficiency and deliver superior dose distributions. Acceptance testing and commissioning of the dynamic MLC (DMLC) option on a dual-energy accelerator was accomplished. Most of the testing was performed using segmental MLC (SMLC) IMRT with stop-and-shoot sequences built within the dynamic mode of the DMLC.

Methods and Materials: The MLC IMRT fields were forward planned using a three-dimensional treatment planning system. The 14 fields were condensed to 7 SMLC IMRT fields with two segments each. In this process, steps were created by moving the leaves to the reduced field positions. No dose (<0.01%) was delivered during this motion. The monitor units were proportioned according to the planned treatment weights. Film and ionization chamber dosimetry were used to analyze leaf positional accuracy and speed, output, and depth-dose characteristics. A geometric phantom was used for absolute and relative measurements. We obtained a volumetric computerized tomography (CT) scan of the phantom, performed 3D planning, and then delivered a single treatment fraction.

Results: The acceptance testing and commissioning demonstrated that the leaves move to programmed positions accurately and in a timely manner. We did find an 1 mm offset of the set leaf position and radiation edge (50%) due to the curved-end nature and calibration limitations. The 7-field SMLC IMRT treatment duplicated the 14-field static plan dose distribution with variations no greater than 1.5%.

Conclusions: The MLC IMRT approach will improve efficiency because the number of electronic and chart entries has decreased by a factor of 2. Portal images are able to capture the initial and final MLC segments. The question of differential daily dose to the prostate and seminal vesicles remains.     

Intensity modulated radiation therapy with multileaf collimators of different leaf widths: a comparison of achievable dose distributions.

PURPOSE: A planning study to analyze the impact of different leaf widths on the achievable dose distributions with intensity modulated radiation therapy (IMRT). METHODS: Five patients (3 intra- and 2 extra-cranial) with projected planning target volume (PTV) sizes smaller than 10 cm by 10 cm were re-planned with four different multileaf collimators (MLC). Two internal collimators with an isocentric leaf width of 4 and 10 mm and two add-on collimators with an isocentric leaf width of 2.75 and were evaluated. The inverse treatment planning system KonRad (Siemens Medical Solutions) was used to create IMRT 'step & shoot' plans. For each patient the same arrangement of beams and the same parameters for the optimization were used for all MLCs. The beamlet size for all treatment plans was chosen to coincide with the leaf width of the respective MLC. To evaluate the treatment plans 3D dose distributions and dose volume histograms were analyzed. As indicators for the quality of the PTV dose distribution the minimum dose, maximum dose and the standard deviation were used. For the organs at risk (OAR) the equivalent uniform dose (EUD) was calculated. To measure the dose coverage of the PTV the volume (V(90)) that received doses higher than 90% of the prescribed dose was calculated where for the conformity the dose conformity index given by Baltas et al. was determined. RESULTS: The MLC with the smallest leaf width yields the best mean value of all five patients for the PTV coverage and for the conformity. For the MLCs with the same leaf width, the add-on MLC leads to superior treatment plans than the internal MLC. This is due to the sharper penumbra of the add-on MLC. The number of IMRT field segments to deliver increased by approximately a factor of two if 2. MLC leafs are used instead of the standard 10 mm leafs. In case of the para-spinal patients the EUD value for the spinal cord is only reduced slightly by using MLCs with leaf widths smaller than 5 mm. For the intra-cranial the EUD value for some organs improved with reduced leaf widths while for some organs the 10 mm MLC leafs give comparable values. CONCLUSION: As expected the MLC with the smallest leaf width always yields the best PTV coverage. Reducing the leaf width from 4 to 2.75 mm results in a slight enhancement of the PTV coverage. With the selected organ parameters no significant improvement for most OAR was found. The disadvantage of the reduction of the leaf width is the increasing number of segments due to the more complex fluence patterns and therefore an increased delivery time.     

Monaco计划系统控制点统计不确定度选择对鼻咽癌剂量计算影响

目的:探讨Monaco计划系统控制点统计不确定度的选择对鼻咽癌剂量分布的影响,给出蒙特卡罗计算中满足临床的单个控制点统计不确定度。方法:设置9个等机架角度间隔的10 cm×10 cm方野并随机抽取5例9个野调强放疗(IMRT)和5例容积调强弧形治疗(VMAT)鼻咽癌计划,以各自计划CT作为质量保证模体创建验证计划,计算...     

模拟呼吸运动对肿瘤三维技术放疗的剂量分布影响

目的 通过模拟呼吸运动研究呼吸运动对三维技术放疗剂量分布的影响。方法 对11例肺癌患者进行三维技术放疗计划设计,将二维半导体阵列Mapcheck放在呼吸模拟运动平板3 cm等效水模上,使用近似呼吸运动周期为3.5 s,运动幅度分别为±3、±5、±10、±15 mm,比较运动和静止状态下Mapcheck实测的剂量分布和治疗计划系统输出的相应平面剂量分布。两组数据行配对t检验。结果 呼吸运动均能降低靶区剂量分布的适形度,剂量分布产生模糊效应;11例患者呼吸运动状态下,3DCRT-QA的γ通过率平均值(3%/3 mm)均大于动态IMRT-QA的,且相互比较的P均<0.05;通过Mapcheck系统分析出呼吸运动对3DCRT剂量分布的影响主要集中在靶区周边,可对动态IMRT的影响分布于整个靶区。结论 对呼吸运动幅度较大的肿瘤建议采用3DCRT技术,更能确保运动的肿瘤得到预期较准确的剂量分布,若采用IMRT技术应根据情况对运动肿瘤进行呼吸运动补偿等方法以确保肿瘤相对静止。