螺旋断层放疗在分段全身照射中上下靶区衔接处剂量分布的影响因素研究

目的 选取10例身高在120.0 cm左右的急性白血病患者分上下两段行螺旋断层治疗（HT）实现全身照射（TBI）,通过分析衔接处靶区剂量分布的变化情况,寻找最佳靶区间隔距离所对应的计划设计参数。方法 选取的研究对象使用德国Siemens公司定位CT获得层厚为5 mm的全身图像,同时在髌骨上方10 cm处放置铅丝,作为上下两段靶区的分割线。在美国瓦里安Eclipse 13.5医生工作站进行靶区和危及器官的勾画,其中上下靶区在铅丝分割处依次分别内收不同距离,然后传至HT计划工作站进行计划设计,其中射野宽度（FW）分别选择5.0、2.5、1.0 cm,螺距分别选择0.430与0.287,调制因子1.8,剂量计算网格（最精细：0.195 cm×0.195 cm）,其余计划参数都保持一致。将其分两段照射的上下靶区依据不同参数进行计划设计,并将设计好的不同参数的计划分别对应叠加在一起进行分析衔接处靶区剂量分布的变化情况。结果 通过比较不同螺距和射野宽度所对应不同间隔距离的衔接处靶区的剂量分布,发现只有射野宽度才影响衔接处靶区的剂量分布：当射野宽度为5.0 cm时,靶区间隔距离为5.0 cm在衔接处的剂量分布最佳;同理当射野宽度为2.5和1.0 cm时,靶区间隔距离分别为2.0和1.0 cm时最佳,即衔接处靶区的最佳剂量分布所对应的间隔距离与射野宽度保持一致。而螺距对衔接处靶区剂量和总治疗时间比值没有影响,总治疗时间长度与射野宽度保持一致反比关系。结论 对于HT进行分段式TBI治疗时,采用如上的计划设计参数,同时靶区勾画时间隔距离与射野宽度保持一致,能保证在进行分段TBI治疗时衔接处靶区不会出现剂量冷热点,确保了治疗的精确与安全。在实际临床治疗过程中,为达到治疗效果与效率的平衡,需要选择合适的计划参数。     

国产自主研发二维水箱应用于螺旋断层 加速器束流质控的可行性研究

目的 使用国产二维水箱在螺旋断层加速器(TOMO)上测量百分深度剂量(PDD)和射野离轴剂量分布,探索其应用于TOMO束流质控的可行性。方法 使用国产二维水箱在TOMO上采集数据。选择40.0 cm × 1.0 cm、40.0 cm × 2.5 cm、40. 0 cm × 5.0 cm 3个射野测量水下1.5、5.0、10.0、15.0、20.0 cm深度的横向离轴剂量分布,选择25.0 cm × 1.0 cm、25.0 cm × 2.5 cm、25.0 cm × 5.0 cm 3个射野测量百分深度剂量曲线以及水下1.5、5.0、10.0、15.0、20.0 cm 深度的纵向离轴剂量分布,将所有数据导入TEMS软件进行γ分析。结果 以厂家金标准数据为基准,国产水箱PDD曲线在3个射野条件下基本吻合,建成区差异偏大,PDD₂₀/PDD₁₀相对偏差>1%。横向离轴剂量分布在3个不同射野条件下除20.0 cm外其他4个深度处所测四分之一高宽(FWQM)均<1%;在3个不同射野、不同深度条件下所测数据在2%/1 mm标准下γ值均>1。纵向离轴剂量分布除射野25.0 cm × 1.0 cm外,其他两个射野不同深度条件下所测半高宽(FWHM)均<1%;除射野25.0 cm × 5.0 cm、深度为15.0和20.0 cm外,其他不同射野不同深度条件下所测数据在2%/1%射野宽度的分析标准下γ值均>1。结论 国产二维水箱部分满足TOMO日常质控需求但仍需进一步优化改进以完全满足TOMO的临床验收需求。     

Varian加速器不同的射野形成方式对射野剂量学参数的影响

目的 探讨Varian加速器不同射野形成方式对射野剂量学参数的影响,为治疗计划系统（TPS）数据建模提供理论依据。方法 在准直器（JAW）、多叶光栅（MLC）和准直器跟随多叶光栅（JAW+MLC）3种射野的形成方式下,分别测量百分深度剂量（PDD）、射野离轴量（OAR）及射野总散射因子（Scp）,并对实测数据进行分析比较。结果 3种射野形成方式对中心轴的百分深度剂量影响很小;在加速器的左右方向和枪靶方向,MLC形成的射野均较JAW形成射野大,在左右方向最大可达2.9 mm。在枪靶方向,最大可达1.7 mm。在左右方向MLC形成的射野测量曲线的半影较在相同射野大小JAW形成射野的半影大。在枪靶方向MLC形成的射野测量曲线的半影较在相同射野大小JAW形成射野的半影小。在两个方向 JAW+MLC形成射野与JAW形成射野大小与半影均无明显差异。结论 射野的不同形成方式对射野大小、半影、总散射因子有影响,建议做调强放射治疗（IMRT）时,在TPS数据建模过程中,应对MLC射野的剂量参数进行关注。     

调强放疗三维剂量验证系统精度测试及临床应用研究

目的 测试三维剂量验证系统Compass^R测量重建及独立计算剂量的精度,评估其临床应用可行性。方法 设计一系列宽度分别为2、1、0.5 cm的条纹状射野,并选取11例肺部调强放疗（IMRT）计划,使用胶片和电离室对被测系统的平面剂量分布和特定点绝对剂量进行验证测试;使用Compass^R对IMRT模体计划做基于解剖信息的三维剂量验证,验证体积γ通过率、平均剂量偏差等参数。结果 条纹状射野测试,与胶片测量相比,被测系统重建和计算剂量γ通过率大于90%（选用3%/3 mm、2%/2 mm标准）,宽度为0.5 cm射野在半影区内γ通过率略差,被测系统重建和计算剂量曲线与胶片测量的曲线最大偏离分别3.21%和2.70%;IMRT计划特定点绝对剂量偏差在3%以内,最大偏差发生在肺部,IMRT计划等中心平面测量重建与胶片测量的γ通过率平均为（94.65±1.93）% （选用3%/3 mm标准）;三维剂量验证结果,靶区及危及器官的体积γ通过率均大于90%,平均剂量的偏差<1%。结论 测试系统剂量精度可满足IMRT计划验证要求,并能给出与患者解剖结构相关的体积剂量误差与位置误差的信息,有利于评估其对临床的影响。     

鼻咽癌放射治疗的CT模拟定位技术探讨

目的　探讨鼻咽癌放射治疗最佳治疗定位技术。　方法　用 CT模拟定位、三维治疗计划系统,加速器两个等中心、适形射野设计治疗计划并用于患者的放射治疗。　结果　靶区整体剂量分布为处方剂量的 113%~97%, 野之间衔接处剂量可控制在处方剂量的±5%,临床初步疗效及放射反应观察表明效果良好。　结论　鼻咽癌放射治疗使用 CT模拟定位治疗技术靶区整体剂量分布满意,照射技术简便。     

Ⅰ~ⅡB期精原细胞瘤术后放疗中不同厚度低熔点挡铅对睾丸剂量防护的研究

目的 评估精原细胞瘤术后放疗中低熔点挡铅厚度及与射野边缘的距离对健侧睾丸受照剂量的影响。方法 选取1例I期精原细胞瘤术后患者的放射治疗计划,利用Synergy医用直线加速器6 MV X射线在SZMC-IV型仿真人体模型上模拟患者照射。采用PTW 0.6 cm³指型电离室,在距射野边缘不同距离处分别测量无挡铅和有3、5、7、10及15 mm厚度低熔点挡铅屏蔽条件下的吸收剂量,评价不同条件下的剂量防护效果。结果 在上述各挡铅厚度条件下,测量结果的归一化剂量与测量点离射野边界之间的距离呈指数形式衰减。无挡铅时的测量结果相对于靶区处方剂量,由距离射野边缘1 cm处的8.41%降到25 cm处的0.61%。有3、5及7 mm挡铅时,分别由距离射野边缘1 cm处的4.55%、3.98%及3.47%降到25 cm处的0.27%、0.21%及0.17%。有10 mm挡铅时,由距离射野边缘1.5 cm处的2.55%降到25 cm处的0.15%。有15 mm挡铅时,由距离射野边缘2 cm处的1.86%降到25 cm处的0.13%。在处方剂量为26 Gy并且距离射野边缘10 cm或4 cm以上,和处方剂量为36 Gy并且距离射野边缘4 cm以上的条件下,分别采用3、7和15 mm厚度的挡铅屏蔽,能将睾丸的散射剂量降低到0.5 Gy以下。结论 在精原细胞瘤术后常规放疗中,根据不同的处方剂量和照射野范围,采用低熔点铅自制适当厚度的睾丸防护装置,能方便、有效地降低睾丸受照剂量,有利于保护患者的生育能力。     

呼吸幅度对旋转容积调强剂量分布的影响研究

目的 研究呼吸幅度对旋转容积调强放疗(VMAT)剂量分布的影响。方法 采用呼吸运动模拟模体(QUASAR)模拟人体头脚方向的一维呼吸运动,二维电离室矩阵采集不同呼吸幅度等中心层面的剂量分布。通过Verisoft软件及绝对剂量分析,分析采集数据与计划数据比较的剂量分布、等中心绝对剂量百分误差和射野通过率。结果 呼吸运动对靶区等中心点剂量影响小于剂量允许误差5%(t=-22.614~-10.756,P<0.05),使靶区边缘剂量偏高、靶区内热点少、冷点多,且随着呼吸幅度的增大,对靶区整体剂量分布影响越大。6、8、10 mm整个射野γ通过率与静态相比差异有统计学意义(t=3.095、8.685、14.096,P<0.05)。8、10 mm靶区内射野通过率与静态相比差异有统计学意义(t=6.081、9.841,P<0.05)。结论 呼吸运动可导致VMAT剂量传输误差,且误差随靶区运动幅度的增加而升高,且呼吸运动方向靶区边缘的正常组织实际治疗受照剂量高于计划评价。     

运用ArcCHECK实施宫颈癌超长靶区的剂量验证

目的初步探讨运用ArcCHECK对宫颈癌超长靶区进行剂量验证的可行性。方法回顾性选取超长靶区(靶区长度≥ 26 cm)和常规靶区(靶区长度< 26 cm)的宫颈癌患者各50例, 运用容积旋转调强放疗(VMAT)技术完成计划设计, 使用ArcCHECK采集验证剂量。在ArcCHECK的中心点处(iso)摆位完成常规靶区组的剂量检测(Short-0 cm), 随后将ArcCHECK沿出床方向平移5 cm(iso 1), 分别完成超长靶区组(Long-5 cm)和常规靶区组(Short-5 cm)的剂量检测。分析各组计划的几何参数(靶区长度和靶区体积)、机器参数(机器跳数和照射时间), 以及在不同检测条件下的γ通过率。结果超长靶区组的靶区长度、靶区体积、机器跳数和照射时间均大于常规靶区组(t = 2.61～18.56, P < 0.05), 常规靶区组在iso 1处的γ通过率明显低于iso处的γ通过率(t = 2.14～8.17,P < 0.05)。在iso 1处, 超长靶区组的γ通过率明显低于常规靶区组(t = -4.70～-2.73,P < 0.01)。各组γ通过...     

6MV医用电子直线加速器的蒙特卡罗模拟

目的 探讨入射电子束的能量和径向强度分布对百分深度剂量曲线和离轴比的影响,并寻找与百分深度剂量曲线和离轴比的测量值最接近的两者参数组合.方法 利用OMEGA/EGSnre系统,模拟Varian 600C医用电子直线加速器,计算水模体百分深度剂量曲线和10 cm深度处离轴比.若测量值和计算值的相对误差经过剂量最大点后在2%之内,则接受入射电子束值.结果 电子束的能量在经过剂量最大点后对深度剂量曲线没有明显影响.离轴比对能量敏感,能量越高,离轴比尖角越小.径向强度分布对深度剂量曲线在误差允许的范围内没有影响,而离轴比曲线对电子束径向强度分布非常敏感.随着径向强度分布半高全宽增大而减小.深度剂量曲线的计算值与测量值一致.在射野范围内,离轴比曲线计算值和测量值一致;但在半影区和射野外,个别测量点的最大误差达到了18.5%.结论 在射野内找到了电子柬能量和径向强度分布的最优参数组合,而在半影区和射野外,未能找到合适的两者参数组合.     

基于二阶导数的小跳数射野删减优化在射波刀头部计划中的应用

目的研究射波刀治疗计划系统中不同的小跳数(MU)射野删减优化方法对颅脑肿瘤计划剂量计算结果的影响。方法选取2021年6月至2022年2月在本院治疗的17例脑转移瘤患者, 针对每例患者使用射波刀VSI系统配备的MultiPlan计划系统设计计划作为无优化组, 每例初始计划生成后需删减一些小MU射野, 以优化计划的执行效率, 形成经验组和优化组。经验组按照经验将30 MU以下的射野删掉, 优化组将基于二阶导数方法计算的MU值以下的射野删掉, 最后统计对比3组计划参数。主要评估的参数包括节点数、射野数、总MU数、预计治疗时间、计划靶区(PTV)所接受的2%、95%体积的剂量PTVD2、PTVD95和平均剂量PTVDmean, 脑组织的平均剂量Dmean-Brain、适形指数(CI)、新适形指数(nCI)、梯度指数(GI)、覆盖率、脑干和左右眼晶状体的最大剂量(Dmax-BS、Dmax-LL和Dmax-RL), 距离PTV 20和40 mm的剂量壳的平均剂量Shell20和Shell40。结果采用的两种优化方法均可以满足>98%PTV接受处方剂量照射。无优化组、经验组和优化组在节点数(H...     

Investigation of Pitch and Jaw Width to Decrease Delivery Time of Helical Tomotherapy Treatments for Head and Neck Cancer

Helical tomotherapy plans using a combination of pitch and jaw width settings were developed for 3 patients previously treated for head and neck cancer. Three jaw widths (5, 2.5, and 1 cm) and 4 pitches (0.86, 0.43, 0.287, and 0.215) were used with a (maximum) modulation factor setting of 4. Twelve plans were generated for each patient using an identical optimization procedure (e.g., number of iterations, objective weights, and penalties, etc.), based on recommendations from TomoTherapy (Madison, WI). The plans were compared using isodose plots, dose volume histograms, dose homogeneity indexes, conformity indexes, radiobiological models, and treatment times. Smaller pitches and jaw widths showed better target dose homogeneity and sparing of normal tissue, as expected. However, the treatment time increased inversely proportional to the jaw width, resulting in delivery times of 24 ± 1.9 min for the 1-cm jaw width. Although treatment plans produced with the 2.5-cm jaw were dosimetrically superior to plans produced with the 5-cm jaw, subsequent calculations of tumor control probabilities and normal tissue complication probabilities suggest that these differences may not be radiobiologically meaningful. Because treatment plans produced with the 5-cm jaw can be delivered in approximately half the time of plans produced with the 2.5-cm jaw (5.1 ± 0.6 min vs. 9.5 ± 1.1 min), use of the 5-cm jaw in routine treatment planning may be a viable approach to decreasing treatment delivery times from helical tomotherapy units.     

Dosimetric characterization of a multileaf collimator]

INTRODUCTION: We studied the dosimetric characteristics of a multileaf collimator (MLC) installed on a dual energy accelerator with 6 and 18 MV photon beams in the Radiotherapy Department of Mauriziano Umberto I Hospital in Turin initiating its use in clinical practice. In particular, measurements included transmission through and between the leaves and at the junction under closed-leaves, central axis percentage depth dose, output factors and effective penumbra. MATERIAL AND METHODS: The MLC installed on the dual energy (6 and 18 MV) linear accelerator Varian Clinac 2100 C/D used in our radiotherapy department is an add-on component positioned below the standard jaws; it consists of 40 computer-controlled opposed pairs of 5 cm thick tungsten leaves, each projecting a 1 cm width at the isocenter, and it provides a maximum treatment field of 40 x 40 cm2 at 100 cm SAD. Transmission, penumbra and scalloping values were measured with the standard radiographic film routinary used in our department. A laser scanning photodensitometer (WP102, Wellhofer) with a 450 microns spot was used to obtain the optical density and the relative dose profile. Radiographic films had been calibrated with an ionization chamber, by irradiating samples to known doses; this calibration was used to correct the film scanner readings to dose. Percentage depth doses were also measured in an automatic water phantom (WP600, Wellhofer) for irregular fields defined by either MLC or alloy blocks, in order to test the differences in the build-up region due to the presence of the acrylic accessory tray. Measured and calculated output factors were compared for some irregular fields defined by the MLC. This comparison tested the algorithm accuracy of our Treatment Planning System 3D CadPlan 3.1.1 Varian-Dosetek. RESULTS AND DISCUSSION: For both energies, approximately 2% of the incident radiation on the MLC is transmitted and an additional 0.5% leakage occurs between adjacent leaves. The leakage under closed-leaves junction is remarkable: about 25-33%. Relative depth dose curves are similar for two fields shaped by either MLC or conventional jaws. Skin dose with MLC-shaped field is less (3.5%) than the one with cerrobend block-shaped fields. The monitor unit calculation procedure used in our treatment planning system can be applied to the MLC (the difference is less than 1%). Effective penumbra in MLC-shaped irregular fields is on the average 11 mm, which is slightly wider (2-3 mm) than the conventional cerrobend blocks penumbra. Effective penumbra increases with depth, field width and leaves positioning. CONCLUSIONS: The MLC, if properly used (collimator rotation, jaws and leaves position, high number of fields), can be applied to conformal radiotherapy with good results. The MLC is better than conventional cerrobend blocks both to improve the treatment reproducibility and accuracy, and relative to dosimetric characteristics like dose transmission and skin dose. The use of MLC to modulate beam fluence (IMRT) will permit to modify beam intensity for improved shaping of the treated volume and to overcome the static therapy dosimetric limitations.     

宽体探测器CT探测器组合对影像分辨力影响的实验研究

目的探讨宽体探测器CT在使用不同扫描模式、探测器宽度以及不同探测器位置时对影像高、低对比度分辨力的影响。方法使用GE Revolution CT, 在固定CT容积剂量指数(CTDIvol)情况下对Catphan600模体的高、低对比度分辨力模块进行扫描。逐层扫描模式时, 分别选择40、80、160 mm探测器宽度, 用探测器的足侧边缘、中心和两圈扫描的相邻区域对分辨力模块进行成像。螺旋扫描模式时, 探测器宽度/螺距组合分别为40 mm/0.516、40 mm/0.984、80 mm/0.508、80 mm/0.992 4组, 对位于扫描野的足侧边缘和中心的分辨力模块进行成像。由2名医生读取模体图像, 评估高、低对比度分辨力。结果逐层扫描模式下探测器宽度为80、160 mm时两圈扫描相邻区域, 以及螺旋扫描螺距为0.5时, 所得影像高对比度分辨力为8 LP/cm, 其余各探测器组合时均为7 LP/cm。逐层扫描时80、160 mm探测器足侧边缘区域所得影像1%低对比度可分辨直径为3 mm, 其余条件时可分辨直径为2 mm。螺旋扫描模式40 mm探测器宽度、螺距0.516时所得影像1%低对...     

Adaptation of telecobalt unit for stereotactic irradiation.

We investigated the feasibility of using an isocentric telecobalt unit for advanced treatment techniques, such as stereotactic radiotherapy. To adapt the telecobalt unit (Th780 C) for stereotactic irradiation, collimator inserts of various sizes, collimator mount, and a couch mount suitable for the telecobalt unit were developed, and the characteristics of the narrow beams of Cobalt-60 (60Co) were studied. Comparative study was carried out between the stereotactic radiotherapy plans of 6 MV and 60Co beams using a 3-dimensional (3D) treatment planning system. The beam penumbra of 60Co beams was found to be larger than those of 6 MV beams. The dose-volume histograms (DVH) obtained from the 60Co beam plan were comparable to those obtained from the 6 MV plan. The DVH of nontarget tissue obtained from the plans of the 2 beams were found to be in good agreement to each other. The difference in equivalent fall-off distance (EFOD) for all 3 cases was found insignificant; hence, it can be concluded that the fall-off dose in the dose distribution of the 60Co stereotactic plan is as good as that of the 6 MV stereotactic plan. In all 3 cases for which the treatment plans were compared between 60Co and 6 MV beams, it was observed that the fall-off doses outside the target were similar; therefore, considering 60Co with 5-mm margin is a cost effective alternative for the linac-based stereotactic radiotherapy.     

BeamModulator新型多叶准直器半影的测量

目的 探讨医科达Synergy-S直线加速器配备的微型多叶准直器的半影特性。 方法 利用PTW MP3 三维水箱和PinPoint电离室分别在水中和空气中测量6、10和18 MV X线的射野离轴比曲线,数据处理后得到半影,分析半影随射线能量、模体深度以及叶片位置的变化。结果 6 MV X线在空气中的半影比水中最大剂量深度处的半影小2 mm;叶片端面的半影比叶片侧面的半影大1 mm左右。微型多叶准直器的半影大小与射线能量、模体深度以及叶片位置均有关。相同照射条件下,射线能量从6 MV提高到18 MV,半影增加1~1.5 mm;模体深度从d_max增加至10 cm,半影增加了1.5 mm;叶片位置不同,半影相差1.5~2 mm。结论 叶片的半影与其机械设计与使用条件密切相关。吸收剂量计算和治疗计划设计时需要充分考虑多叶准直器的半影特性。     

Commissioning of mini-multi-leaf-collimator (MMLC) for stereotactic radiosurgery and radiotherapy

Commissioning of a Radionics miniature multi-leaf collimator (MMLC) for stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) is reported. With single isocenter and multi static fields, the MMLC can provide better conformity of dose distributions to the target and/or irregularly shaped target volumes than standard arc (circular) field beams with multiple isocenters. Advantages offered by the MMLC over traditional LINAC based SRS and SRT includes greatly improved dose homogeneity to the target, reduced patient positioning time and reduced treatment time. In this work, the MMLC is attached to a Varian 2300 C/D with Varian 80-leaf multi-leaf collimator. The MMLC has 62 leaves, each measured to a width of 3.53 mm at isocenter, with fields range from 1x1 cm to less than 10 × 12 cm. Beam parameters required by the Radionics treatment planning system (XPlan version 2) for evaluating the dose include tissue maximum ratio (TMR), scatter factors (SF), off-axis ratios (OAR), output factors, penumbra function (P) and transmission factors (TF) are performed in this work. Beam data are acquired with a small stereotactic diode, standard ion chambers and radiographic films. Measured profiles of dose distribution are compared to those calculated by the software and absolute dosimetry is performed.     

The Clatterbridge high-energy neutron therapy facility: specification and performance

A new high-energy neutron therapy facility has been installed at the Douglas Cyclotron Centre, Clatterbridge Hospital, Merseyside, in order to extend the clinical trials of fast neutrons initiated by the Medical Research Council. The neutron beam is produced by bombarding a beryllium target with 62 MeV protons. The target is isocentrically mounted with the potential for 360 degrees rotation and has a fully variable collimator. This gives a range of rectilinear field sizes from 5 cm x 5 cm to 30 cm x 30 cm. Basic neutron beam data including output, field flatness, penumbra and depth-dose data have been measured. For a 10 cm x 10 cm field, the 50% depth dose occurs at 16.2 cm in water and the output is 1.63 cGy microA-1 min-1 at the depth of dose maximum. The effectiveness of the target shielding and the neutron-induced radioactivity in the treatment head have also been measured. It is concluded that the equipment meets both the design specifications and also fully satisfies criticisms of earlier neutron therapy equipment. A full radiation survey of the centre was also carried out and it was found that radiation levels are low and present no significant hazard to staff.