Dosimetric characterization of a newly designed encapsulated interstitial brachytherapy source of iodine-125-model LS-1 BrachySeed.

A newly designed encapsulated 125I source has been introduced (Model LS-1 BrachySeed manufactured by DRAXIMAGE Inc.) for interstitial brachytherapy. In this source 125I radionuclide is contained in two ceramic beads positioned at each end of a titanium capsule. The source contains a rod of Pt-Ir, which serves as a radiographic marker for source localization in the patient. Principle photon emissions are 27.4 and 31.0 keV X-rays and a 35.5 keV gamma-ray. The 22.2 and 25.5 keV silver X-rays produced by fluorescence of the silver dopant in the ceramic bead radioisotope carriers, are also emitted. In this work, the dosimetric characteristics of the 125I source were measured with micro LiF TLD chips and dosimetry parameters were characterized based upon the American Association of Physicists in Medicine, Task Group, No. 43 formalism. The corrected 1999 National Institute of Standards and Technology standard for low energy interstitial brachytherapy sources was used to specify the air kerma strength of the sources used in this study. The dose rate constant of the sources was determined to be 1.02+/-0.07 cGy h(-1) U(-1). The radial dose function was measured and was found to be similar to that of the silver-based model 6711 125I source. However, the anisotropy function of the Model LS-1 BrachySeed source is considerably better than that of model 6711 125I source, especially on the points along and close to the longitudinal axis of the source. The BrachySeed model LS-1 provides more isotropic angular dose distribution in tissue than model 6711 125I source. The anisotropy constant for the model LS-1 source was determined to be 1.006, which is considerably better than the value of 0.93 for the model 6711 source.     

Monte Carlo dose parameters of the BrachySeed model LS-1 I brachytherapy source

Using a modified EGS4 code and associated user code DOSCGC, the two-dimensional dose rate distribution in water and air-kerma strength are calculated for a BrachySeed (model LS-1) ¹²⁵I brachytherapy source, based on geometry and material data provided by the manufacturer. The AAPM TG-43 dose parameters derived from these results include the dose rate constant, the radial dose function, the anisotropy function, and the anisotropy factor and constant. The value of the dose rate constant so obtained is 0.932±0.003 cGy h⁻¹ U⁻¹. The source strength calculation excludes the contribution from titanium characteristic X-rays (4.5 and 4.9 keV) in the source in order to comply with a new primary calibration standard implemented by the National Institute of Standards and Technology in 1999. A sampling procedure for simulating silver characteristic X-ray production in the mixture material of the source core is developed in the EGS4 code. The calculated results reveal the good dose isotropy of the LS-1 source. The Monte Carlo dose parameters obtained are compared with measurements and calculations of other investigators.     

Review of AAPM task group no. 43 recommendations on interstitial brachytherapy sources dosimetry

In 1995, the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) published its recommendations on the dosimetry of interstitial brachytherapy sources. The report recommended the use of a new dose calculation formalism based on measured quantities. The formalism in modular form permits the computation of doses in two dimensions for ¹⁰³Pd, ¹²⁵I, and ¹⁹²Ir sources. The TG-43 dose calculation formalism introduced new and updated quantities such as air kerma strength, dose rate constant, radial dose function, anisotropy function and anisotropy factor. The dose rate obtained using the TG-43 dose calculation formalism and updated source dosimetry data can be expected to be different from some of the currently used systems by as much as 17%. For the same treatment and implementing the TG-43 dosimetry with point source approximation, the widely prescribed dose of 160 Gy for ¹²⁵I permanent implants using model 6711 sources changes to 144 Gy. In addition to the dose calculation formalism, TG-43 report also stated that the air kerma strength provided by NIST is estimated to be approximately 7–10% higher than it should be, due to low energy photon contamination for ¹²⁵I. This difference has not been accounted for in the TG-43 report.     

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.     

Experimental determination of the Task Group-43 dosimetric parameters of the new I25.S17plus 125I brachytherapy source

PurposeTo present experimental dosimetry results for the new IsoSeed I25.S17plus ¹²⁵I brachytherapy source, in fulfillment of the American Association of Physicists in Medicine recommendation for, at least one, experimental dosimetry characterization of new low-energy seeds before their clinical implementation.Methods and MaterialsA batch of 100 LiF thermoluminescent dosimeter (TLD)-100 microcubes was used for the experimental determination of the dose-rate constant, radial dose, and anisotropy functions, in irradiations performed using two Solid Water phantoms. Monte Carlo (MC) simulations were used to determine appropriate correction factors that account for the use of Solid Water as a phantom material instead of liquid water and for the different energy response of the TLD dosimeters in the experimental ¹²⁵I photon energies relative to the 6 MV x-ray photon beam used for the TLD calibration. Measurements were performed for four I25.S17plus seeds; one with direct traceability of air-kerma strength calibration to National Institute of Standards and Technology and three with secondary National Institute of Standards and Technology traceability.ResultsA mean dose-rate constant, Λ, of 0.956 ± 0.043 cGy h⁻¹ U⁻¹ was experimentally determined for the I25.S17plus source, which agrees within uncertainties with the MC result of 0.925 ± 0.013 cGy h⁻¹ U⁻¹ calculated independently for the same seed model in a previous study. Agreement was also observed between the measured and the MC-calculated radial dose and anisotropy function values.ConclusionsExperimental dosimetry results for the I25.S17plus ¹²⁵I source verify corresponding independent MC results in the form of Task Group-43 dosimetry parameters. The latter are found in agreement within uncertainties with sources of similar design incorporating a silver marker, such as the Oncura OncoSeed Model 6711.     

Dosimetric characterization of an encapsulated interstitial brachytherapy source of 125I on a tungsten substrate

PURPOSE: Recently, a new design of an encapsulated 125I source using a tungsten substrate has been introduced by Best Medical International and named as Best Model 2301 source. In contrast to model 6711 source that uses silver as substrate, the model 2301 source does not yield fluorescent x rays (22.1 keV and 25.5 keV) in the energy range of dosimetric interest. This changes the dosimetric characteristics of the source and experimental determination of these characteristics is needed. METHODS AND MATERIALS: In this work, the dosimetric characteristics of the tungstenbased 125I source were measured using LiF TLDs in a Solid Water phantom. The dose rate constant as well as the radial dose function and anisotropy function were measured. RESULTS: The dose rate constant for the tungsten-based source was determined to be 1.02 +/- 0.07 cGy h(-1) U(-1) in contrast to the previously reported value of 0.98 for the silver-based model 6711 source. The radial dose function for the tungsten-based model 2301 source decreases slightly less rapidly with distance than that for the silver-based model 6711 source. Considerable differences in the anisotropy functions between the two sources were observed. CONCLUSIONS: Dosimetric parameters of the Model 2301 source, based on AAPM TG-43 formalism, have been experimentally determined.     

Monte Carlo calculations of AAPM Task Group Report No. 43 dosimetry parameters for the (125)I I-Seed AgX100 source model

PurposeThe purpose of this study was to determine the dosimetric parameters of the AgX100, a new ¹²⁵I brachytherapy seed model, using Monte Carlo (MC) simulations according to the protocol specified by the updated American Association of Physicists in Medicine Task Group No. 43 Report (TG-43U1) and compare these parameters with those of the established brachytherapy ¹²⁵I seed models 6711 and I25.S06.Methods and MaterialsIndependent verification of the new seed geometry was performed using high-resolution digital radiography and scanning electron microscopy. MCNPX v.2.5 MC simulations of the AgX100 seed were performed to derive its TG-43U1 parameters, the dose rate constant, the radial dose function, and the two- and one-dimensional anisotropy functions in liquid water. A dosimetric error propagation analysis was also performed to include uncertainty because of seed manufacturing tolerances and physics parameters.ResultsThe MC-calculated dose rate constant for the AgX100 seed was 0.943 cGy·h^?1·U^?1 ± 2.6% (k = 1) based on the air kerma strength for a simulated point detector. Tabulated results of the radial dose function for line and point source approximations and the two-dimensional anisotropy function are also reported.ConclusionsThe MC-predicted dose distribution of the AgX100 seed was found to be comparable with that of the model 6711 seed but much different from the dose distribution of the model I25.S06 seeds. However, at shallow distances, there were some dosimetric differences between the AgX100 and 6711 seed, which warrant separate TG-43U1 parameters for use in clinical treatment planning systems.     

Experimental characterization of the dosimetric properties of a newly designed I-Seed model AgX100 (125)I interstitial brachytherapy source

PurposeTo measure the dosimetric properties of the Model AgX100 ¹²⁵I source for interstitial brachytherapy.Methods and MaterialsThe photon energy spectrum emitted by the AgX100 source was measured using a high-resolution germanium spectrometer customized for low-energy brachytherapy source spectrometry. The dose distribution around the source was measured using the 1 × 1 × 1 mm³ lithium fluoride thermoluminescent dosimeters in water-equivalent solid phantoms. The dosimetric parameters needed for dose calculation using the American Association of Physicists in Medicine Task Group No. 43 (TG-43) formalism were determined and compared with the results of a Monte Carlo simulation by an independent research group and with the TG-43 consensus values of the well-established model 6711 source.ResultsIt was found that (1) the photon energy spectrum emitted by the AgX100 source was nearly identical to that emitted by the model 6711, (2) the dose-rate constant determined by the photon spectrometry technique (0.957 ± 0.037 cGy·h^?1·U^?1) and by the thermoluminescent dosimeter technique (0.995 ± 0.066 cGy·h^?1·U^?1) was within 1.5% of the corresponding values determined for the model 6711 source, and (3) the radial dose function and the anisotropy function of the AgX100 source were also found to be similar to the consensus data established for the model 6711 source in the TG-43 update report.ConclusionsA comprehensive dosimetric characterization has been carried out for the model AgX100 ¹²⁵I source. The American Association of Physicists in Medicine TG-43 dosimetry parameters for this source has been determined from the experimental data.     

组织成分及密度对125I粒子植入剂量分布影响的研究

目的 分析组织成分及密度对¹²⁵I粒子植入剂量分布影响,为临床放射性粒子植入剂量计算和评估提供参考。方法 应用egs_brachy软件建立OncoSeed 6711型¹²⁵I放射性粒子物理模型,计算剂量率常数和水中径向剂量函数g（r）,以验证计算模型准确性;根据不同组织的元素组成及密度表,分别计算¹²⁵I粒子在水、前列腺、乳腺、肌肉、骨等不同介质中g（r）和剂量分布。结果 计算得到的剂量率常数为0.950 cGy·h^-1·U^-1、水中g（r）和吸收剂量均与文献数据近似。在同一径向位置,¹²⁵I粒子在前列腺、肌肉中吸收剂量与水中差异<5%;在距源中心0.05 cm处,骨中吸收剂量是水中的6.042倍;在近源1.7 cm内,乳腺与水中吸收剂量差异均>10%。结论 ¹²⁵I粒子在部分介质中的剂量分布与水有着较明显区别,在临床剂量计算中需考虑组织成分及密度对吸收剂量的影响。     

Development of GATE Monte Carlo Code for Simulation and Dosimetry of New I-125 Seeds in Eye Plaque Brachytherapy

PurposeDose distributions are calculated by Monte Carlo (MC) simulations for two low-energy models ¹²⁵I brachytherapy source—IrSeed-125 and IsoAid Advantage (model IAI-125A)—loaded in the 14-mm standardized plaque of the COMS during treatment of choroid melanoma.MethodsIn this study, at first, the radial dose function in water around ¹²⁵I brachytherapy sources was calculated based on the recommendations of the Task Group No. 43 American Association of Physicists in Medicine (TG-43U1 APPM) using by GATE code. Then, brachytherapy dose distribution of a new model of the human eye was investigated for a 14-mm COMS eye plaque loaded with these sources with GATE Monte Carlo simulation.ResultsResults show that there are good agreements between simulation results of these sources and reporting measurements and simulations. Dosimetry results in the designed eye phantom for two types of iodine seeds show that the ratios of average dose of tumor to sclera, vitreous, and retina for IrSeed (IsoAid) source are 3.7 (3.7), 6.2 (6.1), and 6.3 (6.3), respectively, which represents the dose saving to healthy tissues. The maximum percentage differences between DVH curve of IsoAid and IrSeed seeds was about 8%.ConclusionsOur simulation results show that although new model of the ¹²⁵I brachytherapy source having a slightly larger dimension than IAI-125A, it can be used for eye melanoma treatment because the COMS eye plaque loaded with IrSeed-125 could produce similar results to the IsoAid seeds, which is applicable for clinical plaque brachytherapy for uveal melanoma.     

Dosimetric parameters estimation using PENELOPE Monte-Carlo simulation code: Model 6711 a 125I brachytherapy seed.

The dosimetric parameters for characterization of a low-energy interstitial brachytherapy source (125)I are examined. In this work, the radial dose function, g(r), anisotropy function F(r,theta), and the absolute dose rate, Lambda, around (125)I seed model 6711 have been estimated by means of the PENELOPE Monte-Carlo (MC) simulation code. The results obtained are in good agreement with the corresponding values recommended by TG-43 that are based in experimental and MC published results.     

Study of the IsoAid ADVANTAGE™ 125I brachytherapy source dosimetric parameters using Monte Carlo simulation

Monte Carlo calculations have been performed using the MCNP4C code for an iodine seed design. As the ADVANTAGE? I-125, Model IAI-125 source is commercially available for interstitial brachytherapy treatment, dosimetric characteristics (dose rate constant, radial dose function and anisotropy function) of this source were theoretically determined following the updated AAPM task group 43 (TG-43U1) recommendations. The dose distribution around the seed was calculated with Monte Carlo simulation in liquid water. The Monte Carlo calculated dose rate constant of this source in water was found to be 0.986 cGy h^?1 U^?1, with an approximate uncertainty of 0.4%. The obtained result has been compared with the previous study. Comparison of the calculated dose rate constant with the value presented by Meigooni et al. shows a very good agreement. Also the anisotropy function and the radial dose function for this source are graphically compared.     

Dosimetry for 131Cs and 125I seeds in solid water phantom using radiochromic EBT film

PurposeTo measure the 2D dose distributions with submillimeter resolution for ¹³¹Cs (model CS-1 Rev2) and ¹²⁵I (model 6711) seeds in a Solid Water phantom using radiochromic EBT film for radial distances from 0.06 cm to 5 cm. To determine the TG-43 dosimetry parameters in water by applying Solid Water to liquid water correction factors generated from Monte Carlo simulations.MethodsEach film piece was positioned horizontally above and in close contact with a ¹³¹Cs or ¹²⁵I seed oriented horizontally in a machined groove at the center of a Solid Water phantom, one film at a time. A total of 74 and 50 films were exposed to the ¹³¹Cs and ¹²⁵I seeds, respectively. Different film sizes were utilized to gather data in different distance ranges. The exposure time varied according to the seed air-kerma strength and film size in order to deliver doses in the range covered by the film calibration curve. Small films were exposed for shorter times to assess the near field, while larger films were exposed for longer times in order to assess the far field. For calibration, films were exposed to either 40 kV (M40) or 50 kV (M50) x-rays in air at 100.0 cm SSD with doses ranging from 0.2 Gy to 40 Gy. All experimental, calibration and background films were scanned at a 0.02 cm pixel resolution using a CCD camera-based microdensitometer with a green light source. Data acquisition and scanner uniformity correction were achieved with Microd3 software. Data analysis was performed using ImageJ, FV, IDL and Excel software packages. 2D dose distributions were based on the calibration curve established for 50 kV x-rays. The Solid Water to liquid water medium correction was calculated using the MCNP5 Monte Carlo code. Subsequently, the TG-43 dosimetry parameters in liquid water medium were determined.ResultsValues for the dose-rate constants using EBT film were 1.069±0.036 and 0.923±0.031 cGy U⁻¹ h⁻¹ for ¹³¹Cs and ¹²⁵I seed, respectively. The corresponding values determined using the Monte Carlo method were 1.053±0.014 and 0.924±0.016 cGy U⁻¹ h⁻¹ for ¹³¹Cs and ¹²⁵I seed, respectively. The radial dose functions obtained with EBT film measurements and Monte Carlo simulations were plotted for radial distances up to 5 cm, and agreed within the uncertainty of the two methods. The 2D anisotropy functions obtained with both methods also agreed within their uncertainties.ConclusionEBT film dosimetry in a Solid Water phantom is a viable method for measuring ¹³¹Cs (model CS-1 Rev2) and ¹²⁵I (model 6711) brachytherapy seed dose distributions with submillimeter resolution. With the Solid Water to liquid water correction factors generated from Monte Carlo simulations, the measured TG-43 dosimetry parameters in liquid water for these two seed models were found to be in good agreement with those in the literature.     

Dosimetric influence of seed spacers and end-weld thickness for permanent prostate brachytherapy

PurposeThe aim of this study was to analyze the dosimetric influence of conventional spacers and a cobalt chloride complex contrast (C4) agent, a novel marker for MRI that can also serve as a seed spacer, adjacent to ¹⁰³Pd, ¹²⁵I, and ¹³¹Cs sources for permanent prostate brachytherapy.Methods and MaterialsMonte Carlo methods for radiation transport were used to estimate the dosimetric influence of brachytherapy end-weld thicknesses and spacers near the three sources. Single-source assessments and volumetric conditions simulating prior patient treatments were computed. Volume–dose distributions were imported to a treatment planning system for dose–volume histogram analyses.ResultsSingle-source assessment revealed that brachytherapy spacers primarily attenuated the dose distribution along the source long axis. The magnitude of the attenuation at 1 cm on the long axis ranged from −10% to −5% for conventional spacers and approximately −2% for C4 spacers, with the largest attenuation for ¹⁰³Pd. Spacer perturbation of dose distributions was less than manufacturing tolerances for brachytherapy sources as gleaned by an analysis of end-weld thicknesses. Volumetric Monte Carlo assessment demonstrated that TG-43 techniques overestimated calculated doses by approximately 2%. Specific dose–volume histogram metrics for prostate implants were not perturbed by inclusion of conventional or C4 spacers in clinical models.ConclusionsDosimetric perturbations of single-seed dose distributions by brachytherapy spacers exceeded 10% along the source long axes adjacent to the spacers. However, no dosimetric impact on volumetric parameters was noted for brachytherapy spacers adjacent to ¹⁰³Pd, ¹²⁵I, or ¹³¹Cs sources in the context of permanent prostate brachytherapy implants.     

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。     

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.     

A novel aluminum vanadate ion exchanger and its use for separation of Ba, In and Ag from Cs, Cd and Au, respectively

A newly designed inorganic ion exchanger, based on aluminum vanadate, has been synthesized and characterized by elemental analysis, spectroscopic tools and powdered X-ray diffraction. The insoluble poorly polycrystalline material is highly stable towards thermal and radiation doses and in various chemical environments. The data of exchange capacities of the solid material for the different alkali and alkaline metal ions determined by batch technique show that the compound can be employed as an ion exchanger. The successful radiochemical separations of the no carrier added daughter nuclides; ^137mBa and ^115mIn from their respective parents present in equilibrium mixtures have been carried out using this material. Elutions of ^137mBa and ^115mIn were performed using 0.0426 mol L⁻¹ ascorbic acid solution and 4.0 mol L⁻¹ HCl, respectively, after sorption of the equilibrated mixtures ¹³⁷Cs–^137mBa at 0.01 mol L⁻¹ HCl medium and ¹¹⁵Cd–^115mIn at pH 7.0, respectively. In another column operation, it has been observed that the separation of gold and silver is possible with the help of the eluents, 0.01% alcoholic solution of Rhodamine-B for gold and 0.5% thiourea solution in 0.1 mol L⁻¹ HClO₄ for silver, respectively, after the sorption of no carrier added onto this material at pH 2.0, at a no carrier added level.     

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.