252Cf中子后装治疗机步进精度测量及其剂量偏差研究

目的 研究²⁵²Cf中子后装治疗机步进精度以及步进偏差引起的剂量偏差。方法 利用EBT3胶片测量²⁵²Cf中子源的步进,然后通过Image J软件测量光密度值找到每步²⁵²Cf中子源的中心,计算出每步之间的间隔;利用双电离室法测量²⁵²Cf中子源位置偏差引起的剂量偏差。结果 EBT3胶片测量²⁵²Cf中子源步进精度可达0.01 mm;²⁵²Cf中子源位置偏差<3 mm时,剂量偏差<2.5%。结论 对²⁵²Cf中子源步进精度以及位置偏差的研究可为制订²⁵²Cf中子后装治疗机质量控制标准提供参考。     

Flexitron后装机的临床调试

目的 为满足国家标准和临床需求,对Flexitron后装机的硬件和软件制定临床调试流程、项目内容和测试方法,并建立相关的质量控制规程。方法 临床调试分为硬件、治疗计划系统(TPS)和端对端(ETE)的全流程测试。采用源位置检测标尺测量放射源的到位精度;通过秒表计时、电离室测量、视频分析3种方法检测驻留时间的精度和线性;使用高精度尺测试模拟尺、连接管、源位置检测标尺等测量工具的精度;使用胶片校准标记丝和施源器;使用静电计和井型电离室校准放射源活度。通过实物图像对TPS的显示、重建精度进行评价。采用自制模体完成扫描、计划和剂量测量进行ETE测试。结果 调试项目中的精度检测结果均在可接受的限值之内,源活度测量结果偏差为0.21%,ETE点剂量测量偏差为2.32%,均满足临床使用要求。但精度检测项目中,核磁标记丝的标称和实测值存在2 mm差异,因此基于核磁影像采用标记丝进行管道重建时需要修正。结论 本研究通过总结Flexitron后装机的临床调试经验,制定了后装机、计划系统各项目的质量控制方法及结果的基线水平,为后装机投入临床使用前的调试工作提供了参考。     

瓦里安高剂量率铱源剂量学参数的蒙特卡罗模拟研究

目的 采用美国医学物理师学会（AAPM）和欧洲放射治疗和肿瘤学会（ESTRO）推荐的蒙特卡罗方法对瓦里安GammaMed Plus HDR ¹⁹²Ir源的剂量学参数进行模拟研究。方法 基于EGSnrc蒙特卡罗软件,建立该型号¹⁹²Ir源精确的计算模型。采用公式推导、双线性插值及单位转换等方法,分别得到了单位活度空气比释动能强度、剂量率常数、径向剂量函数以及各向异性函数,并将结果与文献报道数据进行分析比较。结果 研究得到的单位活度空气比释动能强度为9.781×10^-8 U/Bq,剂量率参数为1.113 cGy·h^-1·U^-1,与文献报道的相差在0.4%以内。本研究的径向剂量函数、各向异性函数与文献数据能较好吻合。结论 基于EGSnrc蒙特卡罗软件能对¹⁹²Ir源剂量学特性进行定量研究,这将为进一步研究后装剂量分布,精确评价临床放疗剂量提供理论依据。     

222Rn-220Rn分辨探测器参加国际比对结果分析

目的 提高²²²Rn与²²⁰Rn的累积测量水平,保证测量结果的准确性与可靠性。方法 采用中国疾病预防控制中心辐射防护与核安全医学所的氡课题组（以下简称本实验室）改进的LD-P型²²²Rn-²²⁰Rn分辨探测器参加日本放射线医学综合研究所（NIRS）组织的²²²Rn-²²⁰Rn累积探测器国际比对。将²²²Rn-²²⁰Rn分辨探测器寄往日本,在NIRS的²²²Rn室和²²⁰Rn室进行不同条件下的比对,暴露结束后再寄回本实验室进行蚀刻与分析,测量结果告知NIRS。最后NIRS将²²²Rn与²²⁰Rn暴露参考值回馈本实验室。结果 在高²²²Rn和低²²²Rn条件下,测量值与NIRS提供的参考值的相对百分偏差（RPD）分别为-12.0%、-11.8%;变异系数（COV）分别为3.0%、6.2%。在高²²⁰Rn和低²²⁰Rn条件下,测量值与NIRS提供的参考值的相对百分偏差（RPD）分别为-0.8%、-8.0%;变异系数（COV）分别为6.7%、4.5%。结论 本次比对LD-P型探测器²²²Rn与²²⁰Rn的测量结果均为NIRS规定的Ι级结果（PRD<10%）,比对结果较好。     

测量后装近距离放射治疗192Ir源参考空气比释动能方法学研究

目的 用NE2570剂量仪,2571指形电离室,测量 ¹⁹²Ir源空气比释动能支架,测量1m处 ¹⁹²Ir源参考空气比释动能。 方法将测量支架放在离墙、地面1m处,指形电离室插入有机玻璃测量支架夹具中,源中心距电离室中心的最佳距离是16cm, 源通过后装机的传输系统传输到施源器中,测量源参考空气比释动能。根据 ⁶⁰Co γ射线,250 kVΧ射线空气照射量刻度因子换算为空气比释动能刻度因子,再由内插公式计算 ¹⁹²Ir源空气比释动能刻度因子。对墙、地、空气、测量支架的散射校准因子,通过阴影屏蔽实验得到;对初始光子减弱校准因子;电离室壁产生的电子非均匀校准因子,均由IAEA的1079号报告(近距离放射治疗源的刻度)中查表得到。 结果在相同环境条件下,使用2种测量方法,指形电离室测量 ¹⁹²Ir源空气比释动能,经转换系数计算源外观活度为1.584×10¹¹Bq;井型电离室测量 ¹⁹²Ir源空气比释动能强度,经转换系数计算源外观活度为1.561×10¹¹ Bq,2个结果的相对偏差为 1.4%。结论指形电离室测量源空气比释动能,该物理量与源的结构、尺寸、壳材料、电离室形状、材质和尺寸无关,测量源空气比释动能与源的空气照射量比较,不确定度误差小。     

四川省7台加速器调强放射治疗多叶光栅叶片到位精确度验证方法研究

目的 用放射性免冲洗胶片验证调强放射治疗（IMRT）多叶光栅（MLC）叶片到位精确度方法研究。方法 选择瓦里安、医科达、西门子3个厂家的医用电子直线加速器共7台,用25 cm×25 cm的放射性免冲洗胶片放在30 cm×30 cm、厚3.0 cm的均质固体模体上,厚度2.0 cm的固体模体板覆盖在胶片上面,经CT扫描,影像传给放射治疗计划系统（TPS）制定治疗计划,多叶光栅形成5条条状栅栏野,能量6 MV X射线束,每条栅栏野长3 cm,宽0.6 cm,每条条状野间隔3 cm,在最大剂量点处,胶片到源距离100 cm,每条栅栏野给出监督剂量250 MU。照射后邮寄到国际原子能机构（IAEA）剂量学实验室测量和计算。结果 6台加速器胶片测量与TPS计划每条栅栏野MLC条状位置偏差符合IAEA要求的±0.5 mm,1台加速器偏差不符合要求。7台加速器胶片测量每对与每条多叶光栅叶片位置偏差均在IAEA要求0.5 mm以内,符合要求。6台加速器胶片测量每对与每条所有MLC叶片实际宽度差值在0.75 mm范围内,1台加速器为-0.8 mm,不符合要求。6台加速器胶片测量每条多叶光栅叶片实际宽度标准偏差在0.3 mm范围内,符合要求。1台加速器为0.4 mm,不符合要求。结论 用放射性免冲洗胶片验证调强放射治疗多叶光栅片到位精确度的方法简单,快速精确,建议广泛应用到临床。     

湖北省7台医用直线加速器调强放射治疗多叶光栅叶片到位精度验证方法研究

目的 用放射性免冲洗胶片测量调强放射治疗（IMRT）多叶光栅（MLC）叶片到位精确度验证方法研究,为IMRT质量控制提供参考依据。方法 选择湖北省7家三甲医院的7台不同型号医用直线加速器,放射治疗计划系统（TPS）计划5条宽度为0.6 cm条状的栅栏,每条状野之间的距离为3.0 cm。用EBT2免冲洗胶片测量5条状野位置、多叶光栅叶片位置偏差和实际宽度。结果 按国际原子能机构（IAEA）要求,胶片测量与TPS计划每条栅栏野多叶光栅条状位置结果应≤±0.5 mm。编号5和编号7的加速器MLC条状野位置偏差分别为0.7和-1.0 mm,不符合IAEA要求。按IAEA要求,胶片测量每对与每条所有多叶光栅叶片平均位置偏差应≤±0.5 mm。7台加速器MLC每对叶片位置偏差均在±0.5 mm内,符合IAEA要求;IAEA要求单对MLC叶片开野宽度与该机器5条条状野平均开野宽度的差值不超过±0.75 mm,7台加速器每对MLC开野宽度与平均值的差值范围为-0.6~0.5 mm,符合要求。所有叶片开野宽度标准偏差应≤0.3 mm,7台加速器标准偏差在0.1~0.2 mm范围内,符合要求。结论 用EBT2免冲洗胶片验证MLC位置精确度方法操作简单、检测精度高,是质量控制（QA）的重要手段之一,适合大范围核查使用。     

南京“5.7”192Ir源放射事故患者早期物理剂量估算

目的 对南京"5.7"¹⁹²Ir源放射事故中,1例局部受大剂量外照射的患者的受照剂量进行快速估算。方法 在获知放射源参数、照射方式和照射时间的基础上,基于东亚人体素体模和受照者主要生理特征,利用蒙特卡罗模拟软件包MCNP建立模型并估算。结果 估算了受照患者16个器官的吸收剂量,数值范围为0.03~9.16 Gy。腿部皮肤的等剂量曲线清晰显示了左、右腿部皮肤的剂量差异。受照者睾丸、前列腺受照剂量较大,吸收剂量数值约9.16 Gy。大腿皮肤受到局部大剂量照射,双腿皮肤剂量估算结果与红外热成像仪探测结果基本一致。结论 结合恰当受照模型的蒙特卡罗技术和模拟软件包可有效用于放射事故患者的早期物理剂量估算。     

后装机192Ir放射源到位精度及剂量重复性测量

后装机治疗 (brachytherapy)是将封装好的放射源 ,通过施源器或输源导管 ,用计算机将放射源植入患者的肿瘤部位进行照射治疗的 1种方法。由于放射源贴近肿瘤组织 ,源的到位精度及到位重复性直接影响肿瘤的辐射剂量分布。后装机1 92 Ir源的到位精度及重复性也是常规质量控制 (QC)和质量保证 (QA)的检查项目。目前已有商品化的QC检测工具[1 ] ,可以方便地完成HDR重要参数检测。当前国内许多放疗单位均未配备QC检测工具 ,本文作者介绍了采用普通直尺及剂量仪等一般工具测量1 92 Ir放射源的到位精度及重复性的方法 ,对临床后装治疗的质量…     

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。     

后装治疗源192 Ir空气比释动能强度检测 与评价

目的 研究用井型电离室测量后装192Ir源空气比释动能强度的方法.方法 用CDX-2000A静电计和HDR 1000井型电离室,现场检测30台后装192Ir源空气比释动能强度,根据源外观活度与空气比释动能强度转换系数,计算源外观活度.用实测源活度与厂家给出的初始源活度比较,相对偏差应在±5%内符合要求.结果 对所有检测的30台后装192Ir源活度与厂家初始源活度比较,相对偏差在-0.1%～4.4%范围内.结论 井型电离室测量法简便,准确度高,在医院可用于质量控制检测.

Abstract：

Objective To study the method of measuring air kerma strength of afterloading units with 192Ir source by using well type ionization chamber.MethodsThe air kerma strength of 30 afterloading units with 192Ir source was measured using 2000A electrometer and 1000 plus well type ionization chamber,and apparent activity of the source was calculated with the air kerma strength and apparent activity conversion factor.The measured activity of the source was compared with the original value of the source provided by the manufacturer,and the relevant deviation should be within ± 5%.Results Theair kerma strength of afterloding units with 192Ir sources was tested.The relevant deviation of the measured activity and the original value was within -0.1%-4.4%.Conclusions The measurement method with a well type ionization chamber is convenient and highly accurate which can be used for the test of quality control in hospitals.     

施源器材料对192Ir后装源水中吸收剂量的影响

目的 应用3D打印支架联合人造金刚石探头测量施源器材料对高剂量率后装¹⁹²Ir源水中吸收剂量的影响。方法 将金刚石探头与塑料插植针分别固定在3D打印支架上,金刚石探头的中心轴与塑料插植针的中心轴在一个平面内相互垂直。采用模拟源尺测量实测驻留位置为248 mm,该驻留位置与逐点测量的最大响应位置吻合。测量材料有304不锈钢、聚亚苯基砜树脂（PPSU）材料、有机玻璃（PMMA）材料和3D打印聚乳酸（PLA）材质。测量水中不同厚度或不同填充率的材料对吸收剂量的衰减。结果 304不锈钢和PPSU材料厚度与相对剂量的线性拟合公式分别为y=-0.029 7x+1.000 3,y=-0.002 3x+1.010 2;拟合优度R²分别为0.925 3和0.722 2。10 mm以内PMMA材料对剂量的影响均<1.5%。3D打印材料填充率（%）与相对剂量的线性拟合公式为y=-0.000 4x+1.024 6,拟合优度R²为0.854 5。结论 施源器材料,尤其是高密度材料（如304不锈钢）和新型技术材料（如3D打印PLA）,对¹⁹²Ir后装源的吸收剂量影响需引起施源器开发人员和临床应用者的足够重视。     

Mechanical evaluation of the Bravos afterloader system for HDR brachytherapy

PurposeThe Bravos afterloader system was released by Varian Medical Systems in October of 2018 for high-dose-rate brachytherapy with ¹⁹²Ir sources, containing new features such as the CamScale (a new device for daily quality assurance and system recalibration), channel length verification, and different settings for rigid and flexible applicators. This study mechanically evaluated the Bravos system precision and accuracy for clinically relevant scenarios, using dummy sources.Methods and MaterialsThe system was evaluated after three sets of experiments: (1) The CamScale was used to verify inter- and intra-channel dwelling variability and system calibration; (2) A high-speed camera was used to verify the source simulation cable movement inside a transparent quality assurance device, where dwell positions, dwell times, transit times, speed profiles, and accelerations were measured; (3) The source movement inside clinical applicators was captured with an imaging panel while being exposed to an external kV source. Measured and planned dwell positions and times were compared.ResultsMaximum deviations between planned and measured dwell positions and times for the source cable were 0.4 mm for the CamScale measurements and 0.07 seconds for the high-speed camera measurements. Mean dwell position deviations inside clinical applicators were below 1.2 mm for all applicators except the ring that required an offset correction of 1 mm to achieve a mean deviation of 0.4 mm.ConclusionsFeatures of the Bravos afterloader system provide a robust and precise treatment delivery. All measurements were within manufacturer specifications.     

Comparison of high-dose rate prostate brachytherapy dose distributions with iridium-192, ytterbium-169, and thulium-170 sources

Purpose

Recent studies have identified that among different available radionuclides, the dose characteristics and shielding properties of ytterbium-169 (¹⁶⁹Yb) and thulium-170 (¹⁷⁰Tm) may suit high-dose rate (HDR) brachytherapy needs. The purpose of this work was to compare clinically optimized dose distributions using proposed ¹⁶⁹Yb and ¹⁷⁰Tm HDR sources with the clinical dose distribution from a standard microSelectron V2 HDR iridium-192 (¹⁹²Ir) brachytherapy source (Nucletron B.V., Veenendaal, The Netherlands).

Methods and materials

CT-based treatment plans of 10 patients having prostate volumes ranging from 17 to 92 cm³ were studied retrospectively. Clinical treatment of these patients involved 16 catheters and a microSelectron V2 HDR ¹⁹²Ir source. All dose plans were generated with inverse planning simulated annealing optimization algorithm. Dose objectives used for the ¹⁹²Ir radionuclide source were used for the other two radionuclides. The dose objective parameters were adjusted to obtain the same clinical target (prostate) volume coverage as the original ¹⁹²Ir radionuclide plan. A complete set of dosimetric indices was used to compare the plans from different radionuclides. A pairwise statistical analysis was also performed.

Results and conclusions

All the dose distributions optimized with specific ¹⁹²Ir, ¹⁶⁹Yb, and ¹⁷⁰Tm sources satisfied the standard clinical criteria for HDR prostate implants, such as those for the Radiation Therapy Oncology Group clinical trial 0321, for combined HDR and external beam treatment for prostate adenocarcinoma. For equivalent clinical target volume dose coverage, the specific ¹⁶⁹Yb and ¹⁷⁰Tm sources resulted in a statistically significant dose reduction to organs at risk compared with microSelectron V2 HDR ¹⁹²Ir source. This study indicates that a ¹⁷⁰Tm or ¹⁶⁹Yb radionuclide source may be an alternative to the ¹⁹²Ir radionuclide sources in HDR brachytherapy.     

Assessment of dose uniformity around high dose rate <Superscript>192</Superscript>Ir and <Superscript>60</Superscript>Co stepping sources

This study aimed to evaluate dose uniformity for ¹⁹²Ir and ⁶⁰Co stepping sources. High dose rate ¹⁹²Ir and ⁶⁰Co stepping sources were simulated by the MCNPX Monte Carlo code. To investigate dose uniformity, treatment lengths of 30, 50, 100, and 150 mm with stepping distances of 3, 5, 7, and 10 mm were considered. Finally, dose uniformity for the ¹⁹²Ir and ⁶⁰Co stepping sources with increasing distances from the source were assessed at these treatment lengths and steps. The findings showed that the dose distribution was non-uniform for regions in close vicinity of the source, especially in the high source steps, but for most points at distances >10 mm from the center of the source, the dose distribution was uniform. For most points, the dose uniformity increased with reduction of the source steps and increments of the transverse distance from the source. The dose non-uniformity was similar for most of the corresponding points of ⁶⁰Co and ¹⁹²Ir sources with the same treatment lengths and source steps, except at the distance of 150 mm. When using stepping technique for the treatment of tumors, more attention should be focused on treatment planning, especially with higher stepping distances and lower transverse distances from the source.     

Experience of using MOSFET detectors for dose verification measurements in an end-to-end 192Ir brachytherapy quality assurance system

PurposeEstablishment of an end-to-end system for the brachytherapy (BT) dosimetric chain could be valuable in clinical quality assurance. Here, the development of such a system using MOSFET (metal oxide semiconductor field effect transistor) detectors and experience gained during 2 years of use are reported with focus on the performance of the MOSFET detectors.Methods and MaterialsA bolus phantom was constructed with two implants, mimicking prostate and head & neck treatments, using steel needles and plastic catheters to guide the ¹⁹²Ir source and house the MOSFET detectors. The phantom was taken through the BT treatment chain from image acquisition to dose evaluation. During the 2-year evaluation-period, delivered doses were verified a total of 56 times using MOSFET detectors which had been calibrated in an external ⁶⁰Co beam. An initial experimental investigation on beam quality differences between ¹⁹²Ir and ⁶⁰Co is reported.ResultsThe standard deviation in repeated MOSFET measurements was below 3% in the six measurement points with dose levels above 2 Gy. MOSFET measurements overestimated treatment planning system doses by 2–7%. Distance-dependent experimental beam quality correction factors derived in a phantom of similar size as that used for end-to-end tests applied on a time-resolved measurement improved the agreement.ConclusionsMOSFET detectors provide values stable over time and function well for use as detectors for end-to-end quality assurance purposes in ¹⁹²Ir BT. Beam quality correction factors should address not only distance from source but also phantom dimensions.     

测量近距离治疗源活度的井型电离室研制

目的研制井型电离室,测量近距离源空气比释动能强度,与国际标准测量物理量接轨,改善源活度的测量精确度,促进国内近距离剂量学的发展。方法吸取国外先进经验,结合本国国情,设计方案,绘制图纸,对井型电离室所有材料进行筛选,加工,组装,并开展性能实验。结果用国外进口的井型电离室和研制的井型电离室在相同条件下比对,结果:井型电离室长期稳定性为0.4%,技术指标为2%;电离电荷复合率为0.9995,技术指标0.9996;井型电离室重复性为0.02%,技术指标为0.5%。井型电离室的最佳驻留位置在平坦峰值区范围内灵敏度固定没有变化,进口井型电离室的最佳驻留位置在平坦峰值5mm范围内灵敏度变化为0.1%。结论该电离室优点:测量快速准确,同时可以测量192Ir,125I和103Pd等放射源活度。测量范围从3.7MBq～7.4×105MBq。该井型电离室将填补我国现场检测仪器的空白,并能形成我国有自主知识产权的产品。