体内金属植入物对放疗剂量分布影响

目的 探讨放射野内金属植入物对其周围组织吸收剂量的影响.方法 将骨科内固定不锈钢板、钛合金板和相同大小条状肌肉分别置入尸体标本左侧股骨前侧,构建实验组与对照组模型.应用直线加速器6 MV X线照射,使用热释光剂量仪分别对不同内植物界面的吸收剂量进行测量,用治疗计划系统对有无金属植入物百分深度剂量变化进行模拟计算并与测量结果 比较.结果 6MVX线照射置入不锈钢板、钛合金板和条状肌肉时,入射面实际测量值分别为1.18 Gy±0.04 Gy、1.12 Gy±0.04 Gy和0.97 Gy±0.03 Gy(F=57.35,P<0.01),不锈钢板和钛合金板较条状肌肉相应位置吸收剂量分别增加了21.65%和15.46%;出射面实际测量值分别为0.87 Gy±0.03 Gy、0.90Gy±0.02 Gy和0.95 Gy±0.04 Gy(F=13.37,P<0.01),不锈钢板和钛合金板较条状肌肉相应位置点吸收剂量分别衰减了8.42%和5.26%.模拟计算钢板入射面1 cm范围内吸收剂量较条状肌肉明显增加,而钢板入射面1 cm以外范围影响<5%,出射面对剂量分布影响<2%.结论 金属植入物对放疗剂量分布存在明显影响,吸收剂量可产生5%～22%偏差;相同条件下不锈钢板对射线剂量分布影响较钛合金板明显.     

金属植入物16-bit CT成像对放疗剂量分布的影响

目的：探索利用CT成像中扩展位深功能重建16?bit CT对金属植入物进行成像,通过比较扫描条件变化对金属CT值影响,分析金属CT值对计算剂量分布影响。方法将不锈钢棒和钛棒插入模体中,采用管电压为120 kV管电流为230 mA条件扫描,得到金属棒12?bit图像及16?bit图像CT值分布。分别在管电流230 mA,管电压分别为100、120、140 kV和管电压120 kV,管电流分别为180、230、280 mA下得到金属棒16?bit 图像CT值分布,并在瓦里安TPS中分别设计为单野和对穿野治疗计划和计算剂量分布。结果不锈钢棒和钛棒12?bit图像CT值均为3071 HU;16?bit图像CT值不锈钢棒比钛棒大。3种管电流下2种金属棒16?bit图像CT值均无明显变化,放疗计划剂量分布也接近。3种管电压下不锈钢棒最大CT值分别为13568、13127、12295 HU;钛棒的分别为8420、7140、6310 HU。结论12?bit图像不能区分不同高密度金属植入物,16?bit图像可得出不同金属CT值分布。金属植入物基于12?bit图像计算的剂量分布与16?bit图像的不同。管电压改变会造成金属植入物CT值明显变化,从而造成放疗剂量分布改变;管电流在一定程度内变化时,金属CT值变化较小,剂量分布差异不明显。     

对金属植入物模体不同剂量计算方法研究

目的 分析比较含有金属植入物的12-bit和16-bit CT图像应用不同算法下剂量的差异。方法 将钛合金棒插入模体中,CT下进行扫描,重建图像得到12-bit和16-bit图像。通过网络传输到Monaco计划系统,设计一个0°的单野,分别用PB算法,CC算法和MC算法计算剂量分布;扩展CT-ED曲线,重新计算剂量。使用Matlab 8.3数据处理软件获取沿射野方向通过金属植入物中心点的深度剂量曲线,对比12-bit和16-bit图像不同算法的剂量分布曲线和距金属植入物入射面与出射面不同距离处的剂量差异。并使用指形电离室进行测量。结果 16-bit CT图像能准确读出金属植入物的CT值,扩展CT-ED曲线后,相对于MC算法,PB算法在金属植入物入射面的剂量降低了5.43%,而在出射面处剂量升高了25.56%,在出射面后方剂量比MC算法结果高。CC算法降低了金属植入物入射面的剂量达4.5%,出射面处的剂量降低了4.31%,在出射面后方降低的更多。MC算法的计算值与测量值最接近。结论 对含有金属植入物的放疗患者,使用16-bit CT图像并扩展治疗计划系统的CT-ED曲线,并利用MC算法可以提高剂量计算的精确度。     

电子束能谱宽度及角分布对蒙特卡罗方法模拟计算剂量分布影响

目的 研究电子束能谱和角分布对其放疗剂量分布影响。方法 应用模拟得到的医用直线加速器电子束能谱分布和角分布作为输入文件,使用经修改的PENELOPE程序中蒙特卡罗方法模拟计算电子束能谱宽度和角分布对射野中心轴剂量分布和离轴剂量分布。结果 电子束能谱宽度和角分布对射野中心轴剂量分布和离轴剂量分布无明显影响,剂量分布曲线几乎重合;只有在能谱展宽为2.5 MeV时才有明显影响,剂量分布曲线有显著差别。结论 根据本研究蒙特卡罗模拟计算结果设计治疗计划系统电子线算法时可不考虑能谱宽度和角分布影响,而直接使用电子线最可几能量计算,这样可节省大约9%时间而有助于提高计算速度。     

热疗用金属热籽对放疗剂量的影响

目的 研究磁感应热疗所用于体内的金属热籽在植入机体后对放疗剂量分布产生的影响.方法 使用放疗人体仿真模型及三维治疗计划系统,通过模拟照射评估用于磁感应热疗的金属植入物处于放疗条件下对剂量分布的影响.结果 所植入的金属棒热籽材料对人体仿真组织的吸收剂量影响≤1.5%.结论 由于在组织中所植入的铁磁热籽对吸收剂量的影响很小,符合靶区剂量总不确定度<5%的要求,因此,在临床放疗处理中可以忽略不考虑其对组织的影响.     

应用密度填充及伪影消减技术提高带金属植入物患者IMRT剂量准确度研究

目的探讨提高带金属植入物患者放射治疗计划剂量计算准确度的方法。方法利用具有金属伪影消减技术的CT模拟机对插入金属棒的CIRS调强模体和8例椎体中植入了钢钉并接受放疗的患者进行扫描,在获得的常规CT图像、金属伪影消减技术CT图像及对其金属区域进行密度填充的图像上设计治疗计划。在模体中比较单个射野及IMRT计划的计算结果与剂量测量结果,同时对患者IMRT计划中金属植入物及其伪影对照射剂量产生的影响进行分析。结果基于常规CT图像的放疗计划中,射野入射路径未通过金属区域时,单个射野的剂量计算误差为3.85%,通过金属区域时射野计算误差范围达4.46%~74.11%。IMRT计划中存在入射路径通过金属区域的射野时,其误差可能超出临床可接受的范围,计算误差随这种射野所占剂量权重的增加而变大。当采用密度填充及伪影消减技术处理图像后,上述单个射野的计算误差分别为1.23%和0.89%~4.73%,IMRT计划的剂量误差为1.84%。若单独采用密度填充技术处理金属区域,IMRT计划的剂量误差为1.88%。基于常规CT图像的患者IMRT计划中,受金属植入物及其伪影的影响,实际靶区受到的最小剂量、平均剂量及处方剂量覆盖率较计划结果下降,危及器官剂量相近。结论基于常规CT图像的放疗计划中,入射路径通过金属区域的射野可能产生较大的剂量计算误差。如果植入的金属材料已知,在计划系统中对金属区域进行密度填充能有效提高计划的剂量计算准确度。伪影消减技术能显著改善图像质量,进一步减少剂量计算误差,对于配备这种功能的CT机进行带金属植入物患者的模拟定位时应作为常规技术。     

金属植入物对放射治疗剂量影响的研究

目的：测量金属内固定支架对放射治疗剂量的影响,对采用金属内固定的肿瘤患者放射治疗提供剂量修正的临床数据。方法：按照测量条件,将带有金属内固定支架的体模在螺旋CT下进行扫描,层厚为5mm,图像通过LANTIS网络传输系统传人放射治疗计划系统（treatment planning system,TPS）中进行模拟计算。按照相同条件,分别用6MV和15MVX线照射,用热释光剂量仪和FAMER型电离室对钛镍合金支架界面以及界面上下一定深度分别测量,并与放射治疗计划系统计算结果比较。结果：实际测量与TPS计算存在一定误差,实测值明显大于TPS计算值,支架前表面的误差最大可达3．9％（6MV）和6．6％（15MV）,支架后表面的误差最大为2．8％（6MV）和6．3％（15MV）,距表面距离越远,误差越小。结论：镍钛合金支架患者放射治疗时,实际测量剂量比TPS计算剂量要大,有可能增加放射性损伤。TPS计算过程中,虽然对金属物进行了密度修正,但仍存在一定误差,有必要在制订放疗计划时对照射剂量进行修正。     

金属植入物对放射治疗剂量影响的研究

目的:测量金属内固定支架对放射治疗剂量的影响,对采用金属内固定的肿瘤患者放射治疗提供剂量修正的临床数据。方法:按照测量条件,将带有金属内固定支架的体模在螺旋CT下进行扫描,层厚为5mm,图像通过LANTIS网络传输系统传入放射治疗计划系统(treatment planning system,TPS)中进行模拟计算。按照相同条件,分别用6MV和15 MVX线照射,用热释光剂量仪和FAMER型电离室对钛镍合金支架界面以及界面上下一定深度分别测量,并与放射治疗计划系统计算结果比较。结果:实际测量与TPS计算存在一定误差,实测值明显大于TPS计算值,支架前表面的误差最大可达3.9%(6MV)和6.6%(15MV),支架后表面的误差最大为2.8%(6MV)和6.3%(15MV),距表面距离越远,误差越小。结论:镍钛合金支架患者放射治疗时,实际测量剂量比TPS计算剂量要大,有可能增加放射性损伤。TPS计算过程中,虽然对金属物进行了密度修正,但仍存在一定误差,有必要在制订放疗计划时对照射剂量进行修正。     

蒙特卡罗算法的乳腺癌术中放疗剂量优化及临床应用

目的 运用蒙特卡罗算法指导乳腺癌IORT剂量优化并评价临床应用效果。方法 利用MCTP的MCBEAM程序建立加速器乳腺癌IORT的模型,采用自主开发的编辑器将乳腺癌患者术前CT图像编辑成术中状态影像,勾画靶区并分别在靶区前后设置不同厚度等效材料和铅板,通过MCSIM程序运算得到等效材料与铅板最佳优化组合。将优化组合应用于 23例IORT患者并观察伤口愈合、不良反应、美容效果和肿瘤复发情况。结果 靶区表面加 2~3 mm等效材料、靶区后缘加5 mm等效材料和2 mm铅板,优化的乳腺癌IORT靶区剂量90%等剂量线基本包绕整个靶区,靶区 V₉₀>90%、V₁₁₀<4%,肺 D_mean<1 Gy。23例患者伤口均愈合良好,未出现感染及不良反应,愈合后和术后半年乳房外观优良率达80%以上,未发现肿瘤复发。结论 蒙特卡罗算法指导下的乳腺癌IORT剂量优化方法可靠,靶区剂量分布均匀、理想,患者无不良反应,美容效果满意,值得临床推广应用。     

金属食管支架对放射治疗剂量分布的影响

目的测量网状自扩金属食管支架对放射线引起的空腔效应及散射效应对放射治疗剂量分布的影响,为食管癌支架置入术后放射治疗的剂量修正提供依据.方法应用模拟食管癌网状自扩金属支架置入术后放射治疗的体模,分别应用60Co γ射线和直线加速器的8 MV X射线进行照射,使用薄窗电离室、热释光剂量仪分别对不锈钢合金支架及钛镍合金支架空腔的界面及界面下一定深度进行了对比测量,并用治疗计划系统对单纯空腔情况下百分深度剂量的变化进行了模拟计算与测量结果进行对照.结果射野7 cm×15 cm 60Co治疗机照射支架前点、后点与无支架均匀水模对应点剂量增加值不锈钢支架分别为1.8%和3.2%,钛镍合金支架分别为1.7%和2.9%.直线加速器的8 MV X射线照射支架前点、后点与无支架均匀水模对应点剂量增加值不锈钢支架分别为1.5%和2.8%,钛镍合金支架分别为1.4%和0.9%.射线经过支架空腔后形成二次建成效应,剂量增加的峰值达7.6%. 结论网状金属食管支架对放射线的散射效应造成的剂量增加<2%,支架空腔形成的二次建成效应,剂量增加>5%. 建议实际放射治疗时须对支架的空腔效应修正计算剂量.     

热塑膜对X射线治疗剂量影响的研究

目的 研究热塑膜对χ射线治疗剂量的影响.方法 运用为模拟放射源而专门开发的BEAMnrc大型蒙特卡罗程序,研究热塑膜在χ射线治疗肿瘤时对皮肤表面剂量的影响.选用本科使用的国产热塑膜(密度为1.12 g/cm3)和模拟密度为1.38 g/cm3的膜,比较不同密度膜对χ射线表面剂量的影响.膜的形态结构分两种,其中一种膜无网孔,另一种膜有网孔.膜的网孔大小有两种,网孔面积分别为0.1 cm×0.1 cm和0.1 cm×0.2 cm,其中网孔与网孔之间的膜材料宽度均为0.1cm.结果 热塑膜的使用主要影响χ射线治疗剂量的建成区,其中0.24 cm厚度下1.38、1.12g/cm3密度无孔膜的表面剂量分别为74.9%、57.0%;1.12 g/cm3密度下0.24、0.12 cm厚度无网孔膜的表面剂量分别为57.0%、41.2%;1.12 g/cm3密度、0.24 cm厚度下无网孔和有网孔膜的表面剂量分别为57.0%、44.5%;1.12 g/cm3密度、0.24 cm厚度、0.1 cm ×0.1 cm、0.1 cm×0.2 cm网孔面积的表面剂量分别为54.1%、44.5%.结论 放疗中热塑膜的使用对患者身体表画吸收的剂量存在较大影响,这种影响的大小和热塑膜材料、孔径和厚度等有关.医生和物理师在做放疗计划设计时,应考虑到热塑膜对患者皮肤剂量影响及其生物效应,必要时采取措施修正,否则可能导致较严重皮肤反应.     

热塑膜对X射线治疗剂量影响的研究

Objective To calculate the effects of thermoplastic mask on X-ray surface dose.Methods The BEAMnrc Monte Carlo Code system, designed especially for computer simulation of radioactive sources, was performed to evaluate the effects of thermoplastic mask on X-ray surface dose.Thermoplastic mask came from our center with a material density of 1.12 g/cm2. The masks without holes,with holes size of 0. 1 cm× 0. 1 cm, and with holes size of 0. 1 cm × 0. 2 cm, and masks with different depth (0.12 cm and 0.24 cm) were evaluated separately. For those with holes, the material width between adjacent holes was 0. 1 cm. Virtual masks with a material density of 1.38 g/cm3 without holes with two different depths were also evaluated. Results Thermoplastic mask affected X-rays surface dose. When using a thermoplastic mask with the depth of 0. 24 cm without holes, the surface dose was 74. 9% and 57.0% for those with the density of 1.38 g/cm3 and 1.12 g/cm3 respectively. When focusing on the masks with the density of 1.12 g/cm3, the surface dose was 41.2% for those with 0.12 cm depth without holes;57.0% for those with 0. 24 cm depth without holes;44. 5% for those with 0. 24 cm depth with holes size of 0.1 cm ×0.2 cm;and 54.1% for those with 0.24 cm depths with holes size of 0.1 cm ×0.1 cm.Conclusions Using thermoplastic mask during the radiation increases patient surface dose. The severity is relative to the hole size and the depth of thermoplastic mask. The surface dose change should be considered in radiation planning to avoid severe skin reaction.     

热塑膜对X射线治疗剂量影响的研究

Objective To calculate the effects of thermoplastic mask on X-ray surface dose.Methods The BEAMnrc Monte Carlo Code system, designed especially for computer simulation of radioactive sources, was performed to evaluate the effects of thermoplastic mask on X-ray surface dose.Thermoplastic mask came from our center with a material density of 1.12 g/cm2. The masks without holes,with holes size of 0. 1 cm× 0. 1 cm, and with holes size of 0. 1 cm × 0. 2 cm, and masks with different depth (0.12 cm and 0.24 cm) were evaluated separately. For those with holes, the material width between adjacent holes was 0. 1 cm. Virtual masks with a material density of 1.38 g/cm3 without holes with two different depths were also evaluated. Results Thermoplastic mask affected X-rays surface dose. When using a thermoplastic mask with the depth of 0. 24 cm without holes, the surface dose was 74. 9% and 57.0% for those with the density of 1.38 g/cm3 and 1.12 g/cm3 respectively. When focusing on the masks with the density of 1.12 g/cm3, the surface dose was 41.2% for those with 0.12 cm depth without holes;57.0% for those with 0. 24 cm depth without holes;44. 5% for those with 0. 24 cm depth with holes size of 0.1 cm ×0.2 cm;and 54.1% for those with 0.24 cm depths with holes size of 0.1 cm ×0.1 cm.Conclusions Using thermoplastic mask during the radiation increases patient surface dose. The severity is relative to the hole size and the depth of thermoplastic mask. The surface dose change should be considered in radiation planning to avoid severe skin reaction.     

Monte Carlo dose calculation on deforming anatomy

This article presents the implementation and validation of a dose calculation approach for deforming anatomical objects. Deformation is represented by deformation vector fields leading to deformed voxel grids representing the different deformation scenarios. Particle transport in the resulting deformed voxels is handled through the approximation of voxel surfaces by triangles in the geometry implementation of the Swiss Monte Carlo Plan framework. The focus lies on the validation methodology which uses computational phantoms representing the same physical object through regular and irregular voxel grids. These phantoms are chosen such that the new implementation for a deformed voxel grid can be compared directly with an established dose calculation algorithm for regular grids. Furthermore, separate validation of the aspects voxel geometry and the density changes resulting from deformation is achieved through suitable design of the validation phantom. We show that equivalent results are obtained with the proposed method and that no statistically significant errors are introduced through the implementation for irregular voxel geometries. This enables the use of the presented and validated implementation for further investigations of dose calculation on deforming anatomy.     

基于蒙特卡罗实现容积调强弧形治疗计划独立剂量验证的应用研究

目的 开发基于蒙特卡罗(MC)的验证平台实现容积调强弧形治疗(VMAT)计划的独立剂量验证。方法 利用EGSnrc/BEAMnrc构建Varian TrueBeam医用直线加速器的机头和准直器模型,并基于机头模型和自编程序搭建患者VMAT计划的独立剂量验证平台,通过平台模拟不同射野大小百分深度剂量(PDD)曲线和离轴比、两个不规则野以及头颈部、胸部和盆腔各1例患者剂量分布。比较不同射野大小PDD曲线和离轴比与蓝水箱测量结果差异,不规则射野与ArcCHECK实测的差异,再通过γ分析法、剂量体积直方图对比分析患者MC模拟剂量、计划系统计算剂量、ArcCHECK实测剂量之间差异,验证平台是否可用于独立剂量验证。结果 对4cm×4cm~40cm×40cm的PDD曲线和离轴比,MC模拟结果和测量结果一致性较好。不规则射野MC模拟结果与ArcCHECK实测相比,在3%/2mm、3%/3mm下γ通过率都在98.1%、99.1%以上;3例不同部位VMAT患者MC模拟剂量和ArcCheck实测剂量在3%/2mm、3%/3mm下γ通过率均好于93.8%、95.9%。通过三维γ分析计划系统计算剂量和MC模拟剂量在3%/3mm下鼻咽癌、肺癌、直肠癌的γ通过率分别为95.2%、98.6%、98.9%;在3%/2mm下依次为90.3%、95.1%、96.7%。结论 基于MC开发的验证平台模拟结果与实际测量结果一致性较好,其模拟结果更接近于患者体内真实剂量分布,初步结果显示可用于VMAT计划的精准独立剂量验证。     

MLC leaf width impact on the clinical dose distribution: a Monte Carlo approach

PURPOSE: The influence of the multileaf collimator (MLC) leaf width on the dose distribution in patients treated with conformal radiotherapy and intensity-modulated radiotherapy has been analyzed. This study was based on the Monte Carlo simulation with the beams generated by a linac with the double-focused MLC. MATERIALS AND METHODS: The transmission through the leaves and the exact shape of the penumbra regions are difficult to model by treatment planning system algorithms. An accurate assessment of the dose variations due to the leaf width change can be achieved by means of Monte Carlo simulation. The BEAM/EGS4 code was used at the Hospital of the Virgen Macarena to model a Siemens PRIMUS linac, featuring an MLC with a leaf width projecting 1 cm at the isocenter. Based on this real model, a virtual head was designed while allowing for a variation of the leaf width projection. Both the real linac and the virtual linac, with leaves projecting 0.5 cm, were used to obtain the dose distributions for several treatments. A few disease sites, including the prostate, head and neck, and endometrium, were selected for the design of the conformal and intensity-modulated radiotherapy treatments with a forward planning algorithm sensitive to the different shapes of the volumes of interest. Isodose curves, differential matrix, gamma function, and the dose-volume histograms (DVHs) corresponding to both MLC models were obtained for all cases. The tumor control probability and the normal tissue complication probability were derived for those cases studied featuring the greatest differences between results for both MLCs. RESULTS: The impact on the DVHs of changing leaf width projections at the isocenter from 1.0 cm to 0.5 cm was low. Radiobiologic models showed slightly better tumor control probability/normal tissue complication probability values using the virtual MLC with a leaf width projecting 0.5 cm at isocenter in those cases presenting greater differences in the DVHs. CONCLUSIONS: The impact on the clinical dose distribution due to the MLC leaf width change is low based on the design and conditions used in this study.