国产血管内^192Ir线源的放射剂量测定

目的 对国产血管内^192Ir线源的剂量分布进行评价，为动物实验和临床应用提供依据。方法 采用KodakX-omatV慢感光胶片，从平行和垂直于放射源长轴方向进行测量，径向测量时间为25、45、65和82s，轴向测定时间为25s，同时进行标准剂量的标定，通过胶片自动分析测量系统分析剂量分布和吸收剂量。参考AAPM TG No.60报告，采用Monte Carlo方法对放射源和辐射剂量进行理论计算，同时与采用AAPM TG No.43报告计算方法进行比较。结果 国产血管内^192Ir线源具有良好的剂量分布。AAPMTGNo.43报告计算方法比Monte Carlo方法高估32％的辐射剂量。结论国产^192Ir线源作为血管内放射源是可行的，采用慢感光胶片测定放射源的剂量分布是一种有效手段。     

高剂量率后装^192Ir源剂量测试研究进展

要现代后装治疗大多采用HDR(高剂量率)微型^192Ir源，其近源区剂量特性常用针点电离室、热释光剂量计测量，但ESR(电子自旋共振)胶片法测量的空间分辨率更高，可达156μm，而蒙特卡罗光子输运模拟方法是衡量测量准确度的金标准。用热释光剂量计进行直肠内剂量测量是预测直肠并发症发生率的良好指针。慢感光胶片测量^192Ir源二维剂量分布精度可达1％．用基于MR(核磁共振)的凝胶剂量计测量^192Ir源三维剂量分布准确度可达2．5％、空间分辨率达1．56mm，光学体层成像凝胶剂量计测量三维剂量分布具有独特的优势。     

高剂量率后装192Ir源剂量测试研究进展

现代后装治疗大多采用HDR(高剂量率)微型192Ir源,其近源区剂量特性常用针点电离室、热释光剂量计测量,但ESR(电子自旋共振)胶片法测量的空间分辨率更高,可达156μm,而蒙特卡罗光子输运模拟方法是衡量测量准确度的金标准.用热释光剂量计进行直肠内剂量测量是预测直肠并发症发生率的良好指针.慢感光胶片测量193Ir源二维剂量分布精度可达1%,用基于MR(核磁共振)的凝胶剂量计测量192Ir源三维剂量分布准确度可达2.5%、空间分辨率达1.56mm,光学体层成像凝胶剂量计测量三维剂量分布具有独特的优势.     

免冲洗胶片法测量后装机192Ir放射源到位精度及步进距离精度

目的 研究使用免冲洗胶片测量后装机¹⁹²Ir放射源到位精度及步进距离精度的方法。方法 使用GAFCHROMIC^® EBT³型免冲洗胶片对1台国产后装机¹⁹²Ir放射源到位精度及步进距离精度进行测量。曝光后的胶片使用EPSON PREFACTION V700 PHOTO胶片扫描仪扫描成胶片分析软件要求的图像格式,然后用SNC Patient 5.2软件中的胶片分析软件对图像进行分析。 结果 以源活性中心为基准点,该后装机使用胶片法测量的¹⁹²Ir放射源到位精度为-0.75 mm。免冲洗胶片分析方法能够分辨2个驻留点间5 mm的步进距离精度,不能够分辨2个驻留点间2.5 mm的步进距离精度;2.5 mm步进距离精度可通过测量3个连续驻留点第1点和第3点间距离是否为5 mm的方法进行间接判断。该后装机使用胶片法测量的连续9个驻留点间的5 mm步进距离无偏差;2.5 mm步进距离精度间接判断结果无偏差。使用胶片法测量的后装机¹⁹²Ir放射源到位精度符合国家标准要求。结论 免冲洗胶片方法可以用于后装机¹⁹²Ir放射源到位精度及步进距离精度的测量。     

胆管癌~(192)lr线源胆管腔内照射的经验

作者应用~(192)Ir源胆管内照射治疗3例胆管癌,将线源留置在前端为盲端的导管内,把此导管经皮经肝插入胆管内腔,~(192)Ir线源腔内照射剂量目前尚无最佳剂量标准,作者考虑到胆管癌对放疗敏感性低,采用距线源5mm处30Gy腔内照射及30Gy外部照射。对腔内照射的适应证尚无定论,Prempree等认为胆管癌小于1.5cm时只腔内照射,大于1.5cm则并用外照射。一般胆管癌发现时多为进行性癌,一般认为腔内照射并外照射者比单纯外照射平均生存期延长,并用腔内照射者平均生存月数为15个月,2年生存率为25%。单纯外照射平均生存     

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…     

经胆管192Ir内照射对犬胆管周围肝组织放射损伤的实验研究

目的:通过研究经胆管192Ir内照射(192Ir-internalirradiation,192 Ir-IIR)对胆管周围肝组织放射损伤,探讨经胆管192 Ir-IIR的有效治疗范围。方法:实验动物为雄性健康杂种犬4只,体重25~30kg。经手术将施源管植入胆管,根据预先设定的剂量及照射点进行胆管内近距离照射。放射源采用192Ir。内照射10天后处死动物,距离胆管壁由近及远按设计距离分别取1mm×1mm×1mm大小肝组织,常规制备光镜切片,作TUNEL染色;同时常规制备电镜切片。光镜下观察周围肝组织的放射损伤同时计数凋亡肝细胞。电镜下观察肝组织超微结构损伤变化并计数凋亡肝细胞。结果:在胆管最大耐受剂量50Gy时,距胆管15mm内肝细胞核出现不可逆性改变。结论:距放射源15mm可以作为有效治疗范围。     

037 源偏离中心和残余斑块对以导管为基础的血管内近距离β源的剂量测定影响

目的：以导管为基础的辐射传递系统使用β和γ放射源能抑制经皮冠状动脉介入术后的再狭窄。放射源在血管腔内偏离中心和残余斑块的存在会影响血管组织的剂量均匀性分布。因此，对临床使用的血管内近距离放射源３２P和９０Sr－９０Y在偏离中心时对血管壁的剂量分布影响进行了调查。方法：计算时假设放射源分别放在血管中心轴上、偏离中心０．５mm和１mm处，血管和周围的组织模拟成均匀分布的水介质，用羟基磷灰石材料，密度为１．４５、１．５５和３．１g／cm３三种模拟不同的斑块；用MCNP４B的蒙特卡罗模拟代码计算剂量，同时考虑残存斑…     

金属内支架对放射治疗影响的体外研究

目的 检测金属内支架是否对放射治疗有影响。方法 采用^192Ir作为放射源，在体外采用平行要反电离室对国产镍钛合金自膨式食管支架、国产不锈钢自膨式胆管式架和不锈钢球囊扩张型血管支架的透射因子进行测定，以确定3种金属支架对射线的衰减情况。结果 研究结果提示，该3种金属支架对射线的透射因子（衰减系数）分别为：0.993,0.,998,0.997，即对射线的衰减分别为：0.7%,1.2%,0.3%。结论 3种金属支架对射线的衰减均不超过1.2%，对金属支架置入后患者的外对照射或支架内近距离治疗的剂量不会造成有临床意义的影响。     

WD—HDR18近距离遥控后装机检修方法2例

WD—HDR18是高剂量率、组织内、腔体内照射治疗遥控后装机，采用微型单粒高活度铱192放射源，利用内装模拟源装置和完整的计算机程序控制，操作简单。但由于真源（铱192）具有辐射，造成了有些故障无法到机房内实际观察和测量，给维修带来不便。这里简单介绍一下后装机两种故障的检修方法。     

Dosimetric characteristics of the <Superscript>192</Superscript>Ir high-dose-rate afterloading brachytherapy source

Purpose  

For the treatment of some cancerous tumors using brachytherapy, an American Association of Physicists in Medicine (AAPM) Task Group No. 43U1 report recommends that the dosimetric parameters of a new brachytherapy source must be determined in two experimental and Monte Carlo theoretical methods before using each new source clinically. This study presents the results of Monte Carlo calculations of the dosimetric parameters for a Ir2.A85-2 brachytherapy source design.     

Retrospective dosimetric comparison of low-dose-rate and pulsed-dose-rate intracavitary brachytherapy using a tandem and mini-ovoids.

The purpose of this study was to compare the dose distribution of Iridium-192 ((192)Ir) pulsed-dose-rate (PDR) brachytherapy to that of Cesium-137 ((137)Cs) low-dose-rate (LDR) brachytherapy around mini-ovoids and an intrauterine tandem. Ten patient treatment plans were selected from our clinical database, all of which used mini-ovoids and an intrauterine tandem. A commercial treatment planning system using AAPM TG43 formalism was used to calculate the dose in water for both the (137)Cs and (192)Ir sources. For equivalent system loadings, we compared the dose distributions in relevant clinical planes, points A and B, and to the ICRU bladder and rectal reference points. The mean PDR doses to points A and B were 3% +/- 1% and 6% +/- 1% higher than the LDR doses, respectively. For the rectum point, the PDR dose was 4% +/- 3% lower than the LDR dose, mainly because of the (192)Ir PDR source anisotropy. For the bladder point, the PDR dose was 1% +/- 4% higher than the LDR dose. We conclude that the PDR and LDR dose distributions are equivalent for intracavitary brachytherapy with a tandem and mini-ovoids. These findings will aid in the transfer from the current practice of LDR intracavitary brachytherapy to PDR for the treatment of gynecologic cancers.     

A quantitative three-dimensional dose attenuation analysis around Fletcher-Suit-Delclos due to stainless steel tube for high-dose-rate brachytherapy by Monte Carlo calculations

PurposeThe commercially available brachytherapy treatment-planning systems today, usually neglects the attenuation effect from stainless steel (SS) tube when Fletcher-Suit-Delclos (FSD) is used in treatment of cervical and endometrial cancers. This could lead to potential inaccuracies in computing dwell times and dose distribution. A more accurate analysis quantifying the level of attenuation for high-dose-rate (HDR) iridium 192 radionuclide (¹⁹²Ir) source is presented through Monte Carlo simulation verified by measurement.Methods and MaterialsIn this investigation a general Monte Carlo N-Particles (MCNP) transport code was used to construct a typical geometry of FSD through simulation and compare the doses delivered to point A in Manchester System with and without the SS tubing. A quantitative assessment of inaccuracies in delivered dose vs. the computed dose is presented. In addition, this investigation expanded to examine the attenuation-corrected radial and anisotropy dose functions in a form parallel to the updated AAPM Task Group No. 43 Report (AAPM TG-43) formalism. This will delineate quantitatively the inaccuracies in dose distributions in three-dimensional space. The changes in dose deposition and distribution caused by increased attenuation coefficient resulted from presence of SS are quantified using MCNP Monte Carlo simulations in coupled photon/electron transport. The source geometry was that of the Vari Source wire model VS2000. The FSD was that of the Varian medical system. In this model, the bending angles of tandem and colpostats are 15° and 120°, respectively. We assigned 10 dwell positions to the tandem and 4 dwell positions to right and left colpostats or ovoids to represent a typical treatment case. Typical dose delivered to point A was determined according to Manchester dosimetry system.Results and ConclusionsBased on our computations, the reduction of dose to point A was shown to be at least 3%. So this effect presented by SS–FSD systems on patient dose is of concern.     

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。     

A Monte Carlo brachytherapy study for dose distribution prediction in an inhomogeneous medium

The purpose of this study was to present a theoretical analysis of how the presence of bone in interstitial brachytherapy affects dose rate distributions. This study was carried out using a Monte Carlo simulation of the dose distribution in homogeneous medium for 3 commonly used brachytherapy seeds. The 3 seeds investigated in this study are iridium-192 (¹⁹²Ir) iodine-125 (¹²⁵I), and palladium-103 (¹⁰³Pd). The computer code was validated by comparing the specific dose rate (Λ), the radial dose function g(r), and anisotropy function F(r,θ) for all 3 seeds with the AAPM TG-43 dosimetry formalism and current literature. The ¹⁹²Ir seed resulted in a dose rate of 1.115 ± 0.001 cGy-hr⁻¹-U⁻¹, the ¹²⁵I seed resulted in a dose rate of 0.965 ± 0.006 cGy/h⁻¹/U⁻¹, and the ¹⁰³Pd seed resulted in a dose rate of 0.671 ± 0.002 cGy/h⁻¹/U⁻¹. The results for all 3 seeds are in good agreement with the AAPM TG-43 and current literature. The validated computer code was then applied to a simple inhomogeneous model to determine the effect bone has on dose distribution from an interstitial implant. The inhomogeneous model showed a decrease in dose rate of 2% for the ¹⁹²Ir, an increase in dose rate of 84% for ¹²⁵I, and an increase in dose rate of 83% for the ¹⁰³Pd at the surface of the bone nearest to the source.     

Dosimetry errors in endovascular high-dose-rate brachytherapy

Monte Carlo data were used to demonstrate the dosimetry of the microSelectron high-dose-rate (HDR) iridium 192 (¹⁹²Ir) stepping source. These data were used to assess the accuracy of the Nucletron brachytherapy planning system (BPS version 13) for peripheral vessel endovascular brachytherapy. Dose rates from the high-dose-rate (HDR) source are calculated using the Monte Carlo code MCNP4A. Calculations are made at 0.25-cm intervals in the longitudinal direction on sleeves of radii of 1 and 0.25 cm. The Monte Carlo data are summed and weighted to simulate the longitudinal dose distribution at a distance of 1 and 0.25 cm from an ¹⁹²Ir source stepping through a straight pathway. A comparison is made between the simulated Monte Carlo dosimetry and the Nucletron brachytherapy planning system’s dosimetry. This study illustrates and quantifies the dosimetric errors at small distances associated with a point source dose calculation algorithm. The effects of step size, dwell time optimization, and active length on the accuracy of BPS v.13 for HDR endovascular brachytherapy are demonstrated.     

A Monte Carlo evaluation of the dosimetric characteristics of the EchoSeed Model 6733 (125)I brachytherapy source

PURPOSE: Recently a new design of a (125)I brachytherapy source was introduced for interstitial seed implants, particularly for prostate seed implants. This new source is the EchoSeed Model 6733 (125)I brachytherapy source. Due to the differences in source design and manufacturing process from one new source to the next, their dosimetric parameters should be determined according to the American Association of Physicists in Medicine (AAPM) TG-43 guidelines. METHODS AND MATERIALS: As per AAPM recommendation, it is required to perform at least one experimental study and one Monte Carlo simulation, preferably done by two independent investigators. Other investigators have experimentally determined the dosimetric parameters of this new source. In this project, the Monte Carlo simulated dosimetric parameters of the EchoSeed Model 6733 source have been provided. RESULTS: The results of this evaluation indicate the value of the dose rate constant of 0.97 +/- 3% cGyh(-1)U(-1) in liquid water, which is in good agreement with the measured value of 0.99 +/- 8% cGyh(-1)U(-1) reported by Meigooni et al. The anisotropy constant of the EchoSeed (125)I brachytherapy source was found to be 0.960 in liquid water. CONCLUSIONS: The Monte Carlo Simulated TG-43 dosimetric parameters of the EchoSeed were determined and the results were compared with the published measured data.     

Comparison of 60Cobalt and 192Iridium Sources in High Dose Rate Afterloading Brachytherapy

PURPOSE: (60)Co sources with dimensions identical to those of (192)Ir have recently been made available in clinical brachytherapy. A longer half time reduces demands on logistics and quality assurance and perhaps costs. MATERIAL AND METHODS: Comparison of the physical properties of (60)Co and (192)Ir with regard to brachytherapy. RESULTS: Required activities for the same air kerma rate are lower by a factor of 2.8 for (60)Co. Differential absorption in tissues of different densities can be neglected. Monte Carlo calculations demonstrate that integral dose due to radial dose fall off is higher for (192)Ir in comparison to (60)Co within the first 22 cm from the source (normalization at 1 cm). At larger distances this relationship is reversed. CONCLUSION: Clinical examples for intracavitary and interstitial applications however, show practically identical dose distributions in the treatment volume.     

6711型125I种子源剂量学参量的蒙特卡罗模拟研究

目的 计算6711型125I种子源的剂量特性.方法 使用EGSnrc蒙特卡罗模拟程序对种子源的各向异性函数、径向剂量函数和剂量率常数进行计算,并给出了不同介质中的空间剂量率分布,将计算结果与美国医学物理师协会(AAPM)TG43-U1号报告中的推荐值和其他已发表的相关数据进行了比较.结果 各向异性函数与其他最新发表的数据符合较好;径向剂量函数与TG43-U1推荐值符合较好;剂量率常数为0.951 cGy·h-1·U-1,与TG43-U1推荐值在1.45%内吻合.结论 6711型125I种子源剂量场具有低剂量率,高梯度的特点;各向异性函数在近距离小角度处存在小突起的结构.     

Evaluation of Scatter Contribution and Distance Error by Iterative Methods for Strength Determination of HDR 192Ir Brachytherapy Source

High-dose rate (HDR) ¹⁹²Ir brachytherapy sources are commonly used for management of malignancies by brachytherapy applications. Measurement of source strength at the hospital is an important dosimetry requirement. The use of 0.6-cm³ cylindrical ionization chamber is one of the methods of measuring the source strength at the hospitals because this chamber is readily available for beam calibration and dosimetry. While using the cylindrical chamber for this purpose, it is also required to determine the positioning error of the ionization chamber, with respect to the source, commonly called a distance error (c). The contribution of scatter radiation (M_s) from floor, walls, ceiling, and other materials available in the treatment room also need to be determined accurately so that appropriate correction can be applied while calculating the source strength from the meter reading. Iterative methods of Newton-Raphson and least-squares were used in this work to determine scatter contribution in the experimentally observed meter reading (pC/s) of a cylindrical ionization chamber. Monte Carlo simulation was also used to cross verify the results of the least-squares method. The experimentally observed, least-squares calculated and Monte Carlo estimated values of meter readings from HDR ¹⁹²Ir brachytherapy source were in good agreement. Considering procedural simplicity, the method of least-squares is recommended for use at the hospitals to estimate values of f (constant of proportionality), c, and M_s required to determine the strength of HDR ¹⁹²Ir brachytherapy sources.