二维电离室点矩阵Matrixx在调强验证中的应用

目的:利用I′mRTMatrixx对适形及调强放射治疗计划二维剂量平面进行验证。通过软件分析确定治疗计划的准确性,提高治疗质量。方法:用Matrixx二维电离室点矩阵系统对适形调强放疗计划进行验证测试,模体为等效固体水,把Matrixx上面加到4.7 cm等效固体水,下面垫5 cm等效固体水,放入CT进行扫描,在计划系统中建成QA模体。然后将治疗计划系统中的适形调强计划放到QA模体上进行特定深度的计算,得到一个剂量平面计划,将该计划输入分析软件中,与同样条件下的实测剂量平面进行分析,比较。结果:通过软件采用Gamma算法,剂量偏差3%,位置偏差3 mm,小于1的r值是96%~100%。结论:Ma-trixx二维电离室点矩阵,在临床中可作为适形计划和调强计划的相对剂量验证工具,而且简单高效。是放疗质量控制的理想剂量验证工具。利用Matrixx阵列能同时较好的实现其绝对剂量和相对剂量的测量。     

一种加速器吸收剂量测量体模的可用性研究

目的：验证使用自制ABS固体体模进行医用电子加速器吸收剂量测量的可行性和可靠性。方法：使用剂量仪在ABS树脂固体体模和标准水箱水中的校准深度处对Varian23EX加速器吸收剂量进行测量,得到使用此体模的测量值相对于在标准水箱水中测量值的修正因子。结果：f介于0.980～1.010,f为ABS固体体模中的吸收剂量相对于标准水箱水中的吸收剂量的比例因子。结论：使用此修正因子对ABS固体体模的测量结果进行修正,该体模可以用于吸收剂量的测量,且使用方便、易于操作、重复性好。     

肺癌调强放射治疗中呼吸运动对靶区剂量分布的影响

目的：肺癌调强放疗的剂量分布易受呼吸运动影响。本研究通过评价静止和模拟运动计划之间的CTV的DVH图、靶区的剂量分布图、适形度指数（CI）和半影变化,旨在评价不同运动幅度的呼吸运动对肺癌靶区剂量的影响程度。材料与方法：选取7例五野调强的肺癌病例计划,分别在瓦里安加速器上进行一次照射,读取出加速器治疗日志文件（Log-files）,再从Pinnacle计划系统中导出两个与射野和中心点有关的文件——plan.TRIAL文件和plan.POINTS文件。根据射野与叶片运动时间的相互关系以及呼吸运动模型,用自编的程序产生两个新的射野和中心点文件。将新文件导回入计划系统,便得到新的模拟运动的计划。比较静止和运动计划的CTV的最大剂量（Dmax）、最小剂量（Dmin）和95%体积所受最小剂量（D95）,以及适形度指数（CI）等来评价运动影响。结果：呼吸运动使7例病例中CTV的Dmin最大降低36%,使D95下降最大值为31%,而Dmax出现无规律的变化。同时,增大呼吸运动幅度,运动计划的80%-20%等剂量线之间包含的体积增大,而靶区的适形度指数减小。结论：呼吸运动产生的模糊效应使靶区边缘处剂量下降,半影扩大,靶区适形度变差。呼吸运动幅度越大,模糊效应越明显。     

碳素纤维床模型对鼻咽癌容积调强技术计划剂量验证的影响

目的研究碳素纤维床模型对鼻咽癌容积调强技术(VMAT)计划剂量验证的影响。方法选取2019年3-6月福建医科大学附属第一医院放疗科治疗的24例鼻咽癌患者作为研究对象。患者均采用容积调强计划设计,在RAYSTATION计划系统中建立两个Delta4验证模体;A模体带有碳素纤维床模型,B模体不带碳素纤维床模型;将所选的24例鼻咽癌容积调强计划在计划系统中分别移植到A模体与B模体上计算剂量,得到验证计划A与验证计划B;用Delta4模体在美国瓦里安Trilogy加速器上进行计划验证,将测量结果与计划A和计划B对比分析,分析的标准为GAMMA 3 mm/3%、GAMMA 3 mm/2%、GAMMA 2 mm/2%、GAMMA 2 mm/1%。结果A组验证计划在不同分析参数下的GAMMA通过率均高于B组验证计划,且两组数据的差异具有统计学意义;3 mm/3%、2 mm/2%分析参数下A、B两组的GAMMA通过率分别为(98.81±1.28)、(97.66±2.34)(P<0.001)和(92.98±3.73)、(89.10±5.11)(P<0.001)。结论碳素纤维床会对鼻咽癌容积调强计划剂量验证产生影响,在设计鼻咽癌验证计划时应考虑加入治疗床模型,以提高验证系统的精确性。     

多层放射性铬胶片剂量验证系统的研制

目的：采用放射性铬胶片（RCF）快速准确地验证调强放射治疗（IMRT）形成的复杂剂量分布,研制多层RCF剂量验证系统。方法：以RCF为载体,利用测量模体、RCF、胶片扫描仪及验证软件的剂量验证系统实施测量及分析;模体模拟人体外形,包含多种专用模块,软件包含二维、三维无标记点配准及验证分析功能。结果：模体凸凹槽结构结合软件无标记点自动定位功能,可快速完成胶片的固定及其与计划数据的配准以及RCF的免冲洗自动显影,减少了调强放射治疗测量和分析的不确定因素,减少物理师工作量。患者调强验证以剂量偏差3%和3 mm距离偏差为控制标准,6个临床病例的伽马分析通过率均＞90%。结论：多层RCF剂量验证系统是调强适形放射治疗剂量验证和常规质量保证的多用途工具,具有方便、准确、真实、海量信息及多用途等特点,可用于对直线加速器、伽玛刀、射波刀、后装机及粒子植入等放射治疗设备质量验证和调强治疗患者剂量的二维、三维验证。     

探讨MatriXX在验证调强放射治疗计划中的应用

目的:通过二维电离室矩阵MatriXX对调强放射治疗计划进行二维剂量分布验证,根据验证结果来探讨其在调强放射治疗计划剂量验证中的应用。方法:利用德国IBA公司的MatriXX二维电离室矩阵及SP34等效固体水模对加速器执行的128例患者的调强放射治疗计划实施测量,获取特定层面二维剂量分布。利用OmniPro I’mRT软件,把患者计划植入模体后计划系统计算的剂量与MatriXX实测得到输出剂量进行比对,然后进行Gamma分析。结果:实际测量的相对剂量分布与计划系统模体中计算的相对剂量分布采用Gamma法(3 mm/3%)和(4 mm/4%)进行分析,以γ值小于1的百分比>95%作为要求,所有计划γ<1的百分比>95%的通过率为100%。结论:MatriXX在验证调强放射治疗计划中具有省时省力、快速简便等优势,是目前剂量验证的较为准确的QA工具之一。     

三维适形放疗中加速器输出剂量率对吸收剂量的影响

目的：探讨三维适形放射治疗中加速器的输出剂量率对吸收剂量的影响。方法：任意选择一个三维适形放射治疗计划,利用剂量仪测量加速器的输出剂量率分别为100、200、300、400、500、600MU／min时的吸收剂量。结果：吸收剂量的偏差随加速器、的输出剂量率的增加而增大,最大值与最小值的相差为0．75％。结论：三维适形放射治疗时,应进行实际测量,并将结果用于指导治疗计划的设计。     

鼻咽癌调强放疗剂量验证的探讨

目的探讨逆向调强适形放疗（IMRT）的剂量学验证方法,保证接受治疗患者剂量的准确性。方法随机抽取30例鼻咽癌患者,进行CT定位扫描,然后把图像传输至核通PLATO三维逆向治疗计划系统,并设计出均分野（七野）治疗计划。利用固体水模板在治疗计划系统中建立三维等效模体,将待验证的IMRT计划套于模体内,分别计算出每野在模体中的剂量分布,选取模体中感兴趣平面上的每野剂量分布,传输至MAPCHECK验证软件系统,在加速器下进行二维剂量模拟照射并与计划系统计算的结果相比较,验证相对剂量和绝对剂量。结果采用DTA方法,剂量位置限定在3%/3mm标准条件下,所有射野中相对量的通过率在85%～100%之间,绝对量的平均通过率在80.7%～100%之间。结论剂量学验证是IMRT临床实施的可靠保证,使用MAPCHECK分析软件进行剂量验证具有适时、方便、快捷的特点,免去了胶片验证法中冲洗、扫描胶片的过程,也减少了大部分的系统误差。因此,MAPCHECK分析软件如今已成为我院剂量验证的常规工具。     

调强放射治疗计划的剂量学验证

目的探讨调强放射治疗计划的剂量学验证方法。方法利用VarianClinacIX直线加速器6MVX线．对Eclipse治疗计划系统设计的调强治疗计划;采用PTW公司的30013型0．6cc电离室配合UNIDOSE型剂量仪及验证模体进行绝对点剂量的验证．采用PTW二维电离室矩阵进行平面剂量的验证。结果绝对点剂量验证结果显示,测量点的测量值与计划值偏差均〈3％。平面剂量验证采用Gamma分析（3mm／3％）,结果是计划的测量点通过率均〉90％。结论实践证明该剂量学验证方法切实有效,简单可行。     

基于MatriXX调强放疗计划的剂量学验证

目的探讨利用二维空气电离室矩阵MatriXX验证调强放疗计划的可行性。方法选择一患者,在美国NOMOS公司CORVOS6.2计划系统设计调强放疗计划,然后将其移植到剂量模体上。将调强放疗计划的计算结果导入MatriXX系统;执行一次完整的调强放疗计划,利用MatriXX测量其输出剂量。通过MatriXX系统的支持软件对调强放疗计划的计算结果和MatriXX测量所得数据进行分析、比较。结果MatriXX系统的支持软件分析,在感兴趣平面高剂量、低梯度区选定某点比较后,得出两者的点剂量差异为0.51%。Gamma分析结果（按3mm和3%的误差标准）95.86%通过。二维等剂量曲线及离轴比具有较好的一致性。结论MatriXX系统验证调强放疗计划简便、可行。     

An open source solution for an in-house built dynamic platform for the validation of stereotactic ablative body radiotherapy for VMAT and IMRT

An in-house solution for the verification of dose delivered to a moving phantom as required for the clinical implementation of lung stereotactic ablative body radiation therapy was developed. The superior–inferior movement required to simulate tumour motion during a normal breathing cycle was achieved via the novel use of an Arduino Uno?, a low-cost open-source microcontroller board connected to a high torque servo motor. Slow CT imaging was used to acquire the image set and a 4D cone beam CT (4D-CBCT) verified the efficacy of contoured margins before treatment on the moving phantom. Treatment fields were delivered to a section of a CIRS? anthropomorphic phantom. Dose verification to the dynamic phantom with Gafchromic EBT3 film using 3 %-1 mm gamma analysis acceptance criteria registered an absolute dose pass rate for IMRT and VMAT of 98 and 96.6 %, respectively. It was verified that 100 % of the PTV received the prescribed dose of 12 Gy per fraction using the dynamic phantom, and no major discrepancy between planned and measured results due to interplay between multileaf collimator sequences and target motion was observed. This study confirmed that the use of an in-house solution using open source hardware and software with existing quality assurance equipment was appropriate in validating a new treatment technique.     

调强放疗CT图像至高剂量率后装治疗CT图像变形配准算法研究

目的 研究一种将调强放射治疗(Intensity Modulated Radiation Therapy,IMRT)图像配准至高剂量后装治疗(high-dose-rate brachytherapy,HDR)CT图像及进行剂量累加的方法。方法 对HDR CT图像中的施源器进行分割以及收缩变形,然后对IMRT CT和收缩后HDR CT进行变形配准,并结合收缩变形后的施源器掩膜图像以确定配准后IMRT CT图像中阴道的位置,并将其扩充,最后完成IMRT-HDR CT的图像变形配准以及剂量的累加。结果利用宫颈癌病人放疗期间获取的IMRT CT和HDR CT图像和相应的剂量分布对算法进行了验证。结果 本文算法能有效消除HDR CT图像中施源器对变形配准的影响,并精确得到病人的受照总剂量。结论 自适应放疗中对总剂量的监测和评价可以让医生根据病人实际的受照剂量,重新优化放疗计划,以实现放射剂量的精确投照。本文提出的方法可以有效实现子宫肿瘤病人的IMRT CT和HDR CT图像的变形配准及剂量的累加,其精度能满足实际临床的需要。     

用60Co射线校准CT电离室的研究

目的探讨CT电离室用60Co射线进行剂量长度乘积刻度的方法。方法 PTW TM30009 CT电离室放在T40017头部模体中心插孔中,用20 cm＆#215;20 cm 60Co射线照射60 s,用UNIDOS剂量仪测量电荷量。相同条件下TM300130.6 mL电离室测量吸收剂量。CT电离室的刻度因子用剂量长度乘积表示。同时测量CT电离室在MV级辐射场中的剂量线性和剂量响应均匀性。结果 CT电离室的剂量-长度刻度因子可以从测量数据计算得到。电离室的剂量线性和剂量响应的均匀性很好。结论用60Co射线进行吸收剂量刻度后,CT电离室可以用于MVCT设备的CT剂量指数测量。     

Development of a dosimetry inter-comparison for IMRT as part of site credentialing for a TROG multi-centre clinical trial for prostate cancer

A methodology has been developed for a dosimetry inter-comparison of intensity modulated radiation therapy (IMRT) delivery in Australasia. The inter-comparison is part of site credentialing for those sites participating in the prostate fractionated irradiation trial (PROFIT) for intermediate-risk prostate patients developed by the Ontario Clinical Oncology Group and coordinated in Australasia by the Trans Tasman Radiation Oncology Group. Features of the dosimetry inter-comparison design included the use of a dedicated pelvic anthropomorphic phantom, the use of a single CT data set of the phantom including contours and the use of radiochromic film as a dosimeter. Action levels for agreement between measured dose and treatment planning system dose have been proposed based on measurement uncertainty and international experience. A trial run of the dosimetry procedure at the reference centre gave results within the predefined action levels.     

The prediction of transmitted dose distributions using a 3D treatment planning system

Patient dose verification is becoming increasingly important with the advent of new complex radiotherapy techniques such as conformal radiotherapy (CRT) and intensity-modulated radiotherapy (IMRT). An electronic portal imaging device (EPID) has potential application for in vivo dosimetry. In the current work, an EPID has been modelled using a treatment planning system (TPS) to predict transmitted dose maps. A thin slab of RW3 material used to initially represent the EPID. A homogeneous RW3 phantom and the thin RW3 slab placed at a clinical distance away from the phantom were scanned using a CT simulator. The resulting CT images were transferred via DICOM to the TPS and the density of the CT data corresponding to the thin RW3 slab was changed to 1 g/cm3. Transmitted dose maps (TDMs) in the modelled EPID were calculated by the TPS using the collapsed-cone (C-C) convolution superposition (C/S) algorithm. A 6 MV beam was used in the simulation to deliver 300 MU to the homogenous phantom using an isocentric and SSD (source-to-surface) technique. The phantom thickness was varied and the calculated TDMs in the modelled EPID were compared with corresponding measurements obtained from a calibrated scanning liquid-filled ionisation chamber (SLIC) EPID. The two TDMs were compared using the gamma evaluation technique of Low et al. The predicted and measured TDMs agree to within 2 % (averaged over all phantom thicknesses) on the central beam axis. More than 90 % of points in the dose maps (excluding field edges) produce a gamma index less than or equal to 1, for dose difference (averaged over all phantom thicknesses), and distance-to-agreement criteria of 4 %, 3.8 mm, respectively. In addition, the noise level on the central axis in the predicted dose maps is less than 0.1 %. We found that phantom thickness changes of approximately 1 mm, which correspond to dose changes on the central beam axis of less than 0.6 %, can be detected in the predicted transmitted dose distributions.     

Investigation of a MOSFET dosimetry system for midpoint dose verification in prostate 3D CRT/IMRT

The suitability of MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) for use in in-vivo dosimetry for IMRT prostate treatment and patient setup errors has been investigated in this work. MOSFETs were placed on entrance and exit surfaces of a number of different phantoms (with varying complexities from homogeneous to anthropomorphic). Dose measurements were then used to calculate a midpoint dose, which was compared with an IC placed at the isocentre. The agreements found between the calculated (MOSFETs) and the measured midpoint dose (IC) was: 0.7 % for a prostate treatment verification and 3.5 % for an IMRT treatment. MOSFETs placed on entry and exit surfaces can detect patient setup offsets of 2 cm, but do not have the sensitivity to confidently detect offsets of 1 cm or smaller.     

MatriXX系统在放疗质控中的应用研究

目的 探讨二维空气电离室矩阵MatriXX系统进行放疗质控监测的准确性、可靠性和方便性。方法 用MatriXX系统在固体水模块中测量医用加速器X射线射野的百分深度剂量(PDD)、组织最大比(TMR)、离轴比、半影和射野宽度,并与RFA300三维水箱扫描结果进行对比分析。MatriXX与自制剂量测量体模相结合验证Pinnac3 V8.0m三维放疗计划系统设计的静态调强和动态调强放疗计划。结果 MatriXX在固体水中所测6MV X射线的PDD和TMR曲线与RFA300水箱扫描曲线基本平行,15MV X射线的PDD曲线与三维水箱扫描结果几乎重合。用MatriXX所测射野半影比三维水箱扫描值大两倍左右,当射野小于3cm×3cm时MatriXX不能自动计算出半影值。MatriXX可在最短采样时间20mS内同时获得射野离轴比、对称性、平坦度、野宽等信息,并能快速准确地完成调强放疗计划二维剂量分布的定量和定性验证。结论 MatriXX在放疗质控测量时具有准确、简便、高效的优势,是较为理想的放疗质控工具。     

Application of Gafchromic film in the study of dosimetry methods in CT phantoms

Gafchromic film has been used for measurement of computed tomography (CT) dose distributions within phantoms. The film was calibrated in the beam from a superficial therapy unit and the accuracy confirmed by comparison with measurements with a 20 mm long ionisation chamber. The results have been used to investigate approaches to CT dosimetry. Dose profiles were recorded within standard CT head and body phantoms and scatter tail data fitted to exponential functions and extrapolated to predict dose levels in longer phantoms. The data have been used to simulate both CT dose index (CTDI) measurements with ionisation chambers of differing length and measurements of cumulative doses with a 20 mm chamber for scans of varying length. The results show that the length of a pencil ionisation chamber is the most significant factor affecting measurements of weighted CTDI (CTDI(w)) and a 100 mm chamber would record 50-61% of the dose measured with a 450 mm one. The cumulative dose measured at the centre of a 150 mm long body phantom records over 70% of the equilibrium dose from a helical scan of a longer phantom. For routine CT dosimetry tests, the determination of correction factors could allow measurements with a 100 mm chamber to be used to derive the CTDI that would be recorded with a longer chamber, and cumulative doses measured with a 20 mm chamber in shorter phantoms to be used to calculate equilibrium doses for helical scans.