检索结果-内蒙古大学图书馆

A pencil-beam photon dose algorithm for stereotactic radiosurgery using a miniature multileaf collimator

MEDICAL PHYSICS 1998年第6期25卷 841-850页

作者： Dong, L Shiu, AM Tung, S Hogstrom, K Univ Texas Md Anderson Canc Ctr Dept Radiat Phys Houston TX 77030 USA

A computer-controlled miniature multileaf collimator (MMLC) with 4 mm leaf width and a maximum field size of 6 cmx6 cm has been designed as a tertiary beam-shaping device for linac-based stereotactic radiosurgery. The purpose of this study is to develop an accurate and efficient dose calculation model for use with the MMLC. A pencil-beam based algorithm using a sum of three Gaussian kernels was developed to model the off-axis ratio of MMLC fields. Because the kernel integration over a rectangular field can be solved in closed form, dose to any point from an arbitrary MMLC field can be calculated efficiently by summing dose contribution from a set of rectangular apertures and transmission blocks that model individual leaf openings or leaf transmissions. The model uses an effective rectangular field and equivalent square method for determination of depth dose and dose output. Results showed that the calculated percentage depth dose was within 1% and output factor was within 1.5% of measured data. The parameters of the pencil beam kernels were extracted by fitting measured off-axis profiles for a few held sizes at a few depths. The accuracy of the calculated off-axis ratio was tested by comparison with measured data for a number of MMLC fields. The algorithm was shown to be accurate to within 1.5% or 1 mm for off-axis ratios. The algorithm computes at a speed of 34 600 data points per second on a DEC Alpha server model 2000/433 (Digital Equipment Corp., Maynard, MA), which is about 15 times faster than a Clarkson-type summation method. (C) 1998 American Association of Physicists in Medicine. [S0094-2405(98)00506-9].

关键词： pencil beam MLC stereotactic radiosurgery irregular field dose algorithm

来源：评论

学校读者我要写书评

暂无评论

A dose calculation algorithm for radiosurgery treatment room shielding optimization

引用

MEDICAL PHYSICS 2023年第6期50卷 3852-3861页

作者： Nygren, Nelly Nordstrom, Hakan da Silva, Joakim Elekta Instrument AB Stockholm Sweden Elekta Instrument AB Kungstensgatan 18Box 7593 SE-10393 Stockholm Sweden

BackgroundMethods described in the literature for designing shielding for treatment rooms for radiotherapy systems often involve assumptions that lead to overestimations of the wall thicknesses required to meet dose rate constraints outside the room. The Leksell Gamma Knife (LGK) has built-in shielding that results in primarily scattered photons leaking into the room. The field of leakage radiation, therefore, has a wide spectrum of energies, up to the primary energies of cobalt-60, and is highly anisotropic, making standard site planning methods difficult to adapt to the LGK. Monte Carlo (MC) simulations are an alternative for dose calculations but are computationally expensive. PurposeThe aim was to develop a dose calculation algorithm for fast estimations of dose rates outside the barriers of a treatment room. The algorithm could then be employed in iterative methods to optimize treatment room parameters such as wall thicknesses and position of the LKG unit. MethodsThe algorithm uses pre-calculated MC simulation data in two steps. First, it uses phase spaces that describe single photons in the radiation field around the LGK. Using each photon's position and direction, they are raytraced to the outside of the room. Based on their energy, angle of incidence to the barrier, and the barrier's thickness, a depth-dose profile is sampled from a pre-calculated library of profiles. The contribution from each photon is added to the space outside the barriers, giving the total dose distribution. The barrier thicknesses are optimized by iteratively running the algorithm and finding the minimum thickness required to keep the resulting maximum dose rate outside below a given upper limit. ResultsComparisons between dose distributions from the dose algorithm and full MC simulations of two typical rooms show good agreement, with the maximum dose rate outside each barrier being estimated within what represents a 2 cm error in concrete barrier thickness. The algorithm is successful

关键词： dose algorithm gamma knife shielding optimization

来源：评论

学校读者我要写书评

暂无评论

Electron pencil-beam redefinition algorithm dose calculations in the presence of heterogeneities

引用

MEDICAL PHYSICS 2001年第10期28卷 2096-2104页

作者： Boyd, RA Hogstrom, KR Starkschall, G Univ Texas MD Anderson Canc Ctr Dept Radiat Phys Houston TX 77030 USA

The electron pencil-beam redefinition algorithm (PBRA) is currently being refined and evaluated for clinical use. The purpose of this work was to evaluate the accuracy of PBRA-calculated dose in the presence of heterogeneities and to benchmark PBRA dose accuracy for future improvements to the algorithm. The PBRA was evaluated using a measured electron beam dose algorithm verification data set developed at The University of Texas M. D. Anderson Cancer Center. The data set consists of measurements made using 9 and 20 MeV beams in a water phantom with air gaps, internal air and bone heterogeneities, and irregular surfaces. Refinements to the PBRA have enhanced the speed of the dose calculations by a factor of approximately 7 compared to speeds previously reported in published data;a 20 MeV, 15X15 cm(2) field electron-beam dose distribution took approximately 10 minutes to calculate. The PBRA showed better than 4% accuracy in most experiments. However, experiments involving the low-energy (9 MeV) electron beam and irregular surfaces showed dose differences as great as 22%, in albeit a small fractional region. The geometries used in this study, particularly those in the irregular surface experiments, were extreme in the sense that they are not seen clinically. A more appropriate clinical evaluation in the future will involve comparisons to Monte Carlo generated patient dose distributions using actual computed tomography scan data. The present data also serve as a benchmark against which future enhancements to the PBRA can be evaluated. (C) 2001 American Association of Physicists in Medicine.

关键词： electron pencil beam electron beam dose algorithm dose algorithm

来源：评论

学校读者我要写书评

暂无评论

Acuros(R)dose verification of ultrasmall lung lesions with EBT-XD film in a homogeneous and heterogeneous anthropomorphic phantom setup

引用

MEDICAL PHYSICS 2020年第11期47卷 5829-5837页

作者： Ollers, Michel C. Swinnen, Ans C. C. Verhaegen, Frank Maastricht Univ GROW Sch Oncol Dept Radiat Oncol Maastro Med Ctr Maastricht Netherlands

Purpose Modern type 'c' dose calculation algorithms like Acuros(R)can predict dose for lung tumors larger than approximately 4 cm(3)with a relative uncertainty up to 5%. However, increasingly better tumor diagnostics are leading to the detection of very small early-stage lung tumors that can be treated with stereotactic body radiotherapy (SBRT) for inoperable patients. This raises the question whether dose algorithms like Acuros(R)can still accurately predict dose within 5% for challenging conditions involving small treatment fields. Current recommendations for Quality Assurance (QA) and dose verification in SBRT treatments are to use phantoms that are as realistic as possible to the clinical situation, although water-equivalent phantoms are still largely used for dose verification. In this work we aim to demonstrate that existing dose verification methods are inadequate for accurate dose verification in very small lung tumors treated with SBRT. Method The homogeneous PTW Octavius4D phantom with the Octavius 1000 SRS detector ("Octavius4D phantom") and the heterogeneous CIRS Dynamic Thorax phantom ('CIRS phantom') were used for dose measurements. The CIRS phantom contained different lung-equivalent film-holding cylindrical phantom inserts ("film inserts") with water-equivalent spherical targets with diameters 0.5, 0.75, 1, 2, and 3 cm. Plans were calculated for 6 and 10 MV for each spherical target in the CIRS phantom, resulting in 14 treatment plans. The plans were delivered to both Octavius4D and CIRS phantom to compare measured dose in a commonly used homogeneous and more realistic heterogeneous phantom setup. In addition, treatment plans of seven clinical lung cancer patients with lung tumors below approximately 1.0 cm(3)were irradiated in the heterogeneous CIRS phantom. The actual tumor size within the clinical treatment plans determined the choice of the spherical target size, such that both measurement geometry and clinical target volumes match as closely as

关键词： Acuros anthropomorphic phantom dose algorithm EBT film small-field dosimetry

来源：评论

学校读者我要写书评

暂无评论

Comparison of Maintenance dose Predictions by Warfarin Dosing algorithms Based on Chinese and Western Patients

引用

JOURNAL OF CLINICAL PHARMACOLOGY 2023年第5期63卷 569-582页

作者： Deng, Jiexin Wang, Yi An, Xiaokang Henan Univ Sch Nursing & Hlth Kaifeng Peoples R China Henan Univ Dept Thorac & Cardiovasc Surg Huaihe Hosp Kaifeng Peoples R China Henan Univ Affiliated Hosp 1 Dept Thorac Surg Kaifeng Peoples R China Henan Univ Jinming CampusJinming Rd North Kaifeng Henan Peoples R China

Warfarin has a long record of safe and effective clinical use, and it remains one of the most commonly prescribed drugs for the prevention and treatment of thromboembolic conditions even in the era of direct oral anticoagulants. To address its large interindividual variability and narrow therapeutic window, the Clinical Pharmacogenetics Implementation Consortium has recommended using pharmacogenetic dosing algorithms, such as the ones developed by the International Warfarin Pharmacogenetics Consortium (IWPC) and by Gage et al, to dose warfarin when genotype information is available. In China, dosing algorithms based on local patient populations have been developed and evaluated for predictive accuracy of warfarin maintenance doses. In this study, percentage deviations of doses predicted by 15 Chinese dosing algorithms from that by IWPC and Gage algorithms were systematically evaluated to understand the differences between Chinese and Western algorithms. In general, dose predictions by Chinese dosing algorithms tended to be lower than those predicted by IWPC or Gage algorithms for the most prevalent VKORC1 and CYP2C9 genotypes in the Chinese population. The extent of negative prediction deviation appeared to be largest in the younger age group with smaller body weight. Our findings are consistent with previous reports that Asians have a higher sensitivity to warfarin and require lower doses than Western populations.

关键词： cardiopharmacology dose algorithm ethnic sensitivity PK PD warfarin

来源：评论

学校读者我要写书评

暂无评论

Comparison between Acuros XB and Brainlab Monte Carlo algorithms for photon dose calculation

引用

STRAHLENTHERAPIE UND ONKOLOGIE 2012年第7期188卷 599-605页

作者： Misslbeck, M. Kneschaurek, P. Tech Univ Munich Klinikum Rechts Isar Klin & Poliklin Strahlentherapie & Radiol Onkol D-81675 Munich Germany

The AcurosA (R) XB dose calculation algorithm by Varian and the Monte Carlo algorithm XVMC by Brainlab were compared with each other and with the well-established AAA algorithm, which is also from Varian. First, square fields to two different artificial phantoms were applied: (1) a "slab phantom" with a 3 cm water layer, followed by a 2 cm bone layer, a 7 cm lung layer, and another 18 cm water layer and (2) a "lung phantom" with water surrounding an eccentric lung block. For the slab phantom, depth-dose curves along central beam axis were compared. The lung phantom was used to compare profiles at depths of 6 and 14 cm. As clinical cases, the CTs of three different patients were used. The original AAA plans with all three algorithms using open fields were recalculated. There were only minor differences between Acuros and XVMC in all artificial phantom depth doses and profiles;however, this was different for AAA, which had deviations of up to 13% in depth dose and a few percent for profiles in the lung phantom. These deviations did not translate into the clinical cases, where the dose-volume histograms of all algorithms were close to each other for open fields. Only within artificial phantoms with clearly separated layers of simulated tissue does AAA show differences at layer boundaries compared to XVMC or Acuros. In real patient CTs, these differences in the dose-volume histogram of the planning target volume were not observed.

关键词： dose algorithm Acuros Monte Carlo AAA

来源：评论

学校读者我要写书评

暂无评论

Independent dose calculations for the Peacock system

引用

Medical Dosimetry 2001年第1期26卷 29-35页

作者： Ayyangar, K.M. Saw, C.B. Shen, B. Enke, C.A. Nizin, P.S. Department of Radiation Oncology UNMC 987521 Nebrasma Medical Center Omaha NE 68198-7521 United States

An independent dose calculation method has been developed to validate intensity-modulated radiation therapy (IMRT) plans from the NOMOS® PEACOCK System. After the plan is generated on the CORVUS planning system, the beam parameters are imported into an independent workstation. The beam parameters consist of intensity maps at each gantry angle and each arc position. In addition, CT scans of the patient are imported into the independent workstation to obtain the external contour of the patient. The coordinate system is defined relative to the alignment point chosen in the CORVUS plan. The independent calculation uses the pencil beam data viz tissue maximum ratio (TMR) and beam profiles for a single 1 × 0.8-cm beamlet formed by the NOMOS® multileaf intensity-modulating collimator (MIMiC) leaf. The pencil beam data were measured for the 6-MV photon beam from Siemens PRIMUS linear accelerator using film dosimetry. The dose at a point is calculated using the depth and off-axis distance from a given pencil beam, corrected for its beam intensity. Isodose distributions are generated using the independent dose calculations and compared to the CORVUS plans. Isodose distributions show good agreement with the CORVUS plans for a number of clinical cases. The independent dose calculation algorithm is described in this paper. Copyright © 2001 American Association of Medical Dosimetrists.

关键词： dose algorithm dose calculation IMRT PEACOCK system Photon beam

来源：评论

学校读者我要写书评

暂无评论

Assessment of warfarin algorithms for hospitalized adults: searching for a safe dosing strategy

引用

JOURNAL OF THROMBOSIS AND THROMBOLYSIS 2019年第4期48卷 570-579页

作者： Cohen, Jessica L. Thompson, Elena Sinvani, Liron Kozikowski, Andrzej Qiu, Guang Pekmezaris, Renee Spyropoulos, Alex C. Wang, Jason J. Northwell Hlth Div Hosp Med Dept Med 300 Community Dr Manhasset NY 11030 USA Northwell Hlth Donald & Barbara Zucker Sch Med Hofstra Northwell Manhasset NY 11030 USA Northwell Hlth Div Hlth Serv Res Ctr Heath Innovat & Outcomes Res Dept Med Manhasset NY 11030 USA Northwell Hlth Syst Lenox Hill Hosp Dept Med Anticoagulat & Clin Thrombosis Serv New York NY 10075 USA

This study evaluates three warfarin dosing algorithms (Kimmel, Dawson, High dose >= 2.5 mg) for hospitalized older adults. A random selection of 250 patients with overshoots (INR >= 5 after 48 h of hospitalization) and 250 patients without overshoots were accessed from a database of 12,107 inpatients >= 65 years treated with chronic warfarin during hospitalization between January 1, 2014 and June 30, 2016. algorithms were retrospectively applied to patients 2 days prior to overshoots in the overshoot group, and 2 days prior to the maximum INR reached after 48 h of hospitalization in the non-overshoot group. Patients were categorized as overdosed or not overdosed and compared using descriptive statistics. Logistic regression modeling determined predictors for overshoots. There was no significant difference between overdose and non-overdose groups for progressing to overshoots by the Kimmel (51.0% vs. 48.7%, p = 0.67) or Dawson (48.5 vs. 57.9%, p = 0.19) algorithms. The Low dose Group (<= 2.5 mg) was significantly more likely to experience an overshoot than the High dose Group (56.6% vs. 45.5%, p = 0.04). The Low dose Group was more likely to be older (81.4% vs. 71.1%, p = 0.02), female (63.5% vs. 49.8%, p = 0.02), weigh less (71.3 +/- 21.9 vs. 79 +/- 23.1, p = 0.002), and be prescribed amiodarone (16.6% vs. 8.1%, p = 0.01). While none of the algorithms predicted overshoots in logistic regression modeling, weight over 70 kg and black race remained protective. The High dose algorithm revealed that providers appropriately gave lower doses to patients at highest risk for warfarin sensitivity. Future studies are needed to investigate tools for inpatient warfarin dosing in older adults.

关键词： Warfarin Inpatients International normalized ratio dose algorithm

来源：评论

学校读者我要写书评

暂无评论

Validation of the acenocoumarol EU-PACT algorithms: similar performance in the Rotterdam Study cohort as in the original study

引用

PHARMACOGENOMICS 2012年第11期13卷 1239-1245页

作者： van Schie, Rianne M. F. el Khedr, Nadia Verhoef, Talitha I. Teichert, Martina Stricker, Bruno H. Hofman, Albert Buhre, Peter N. Wessels, Judith A. M. Schalekamp, Tom le Cessie, Saskia van der Meer, Felix J. M. Rosendaal, Frits R. de Boer, Anthonius Maitland-van der Zee, Anke-Hilse Visser, Loes E. Univ Utrecht Div Pharmacoepidemiol & Clin Pharmacol Utrecht Inst Pharmaceut Sci NL-3508 TB Utrecht Netherlands Royal Dutch Pharmacists Assoc R&D Dept The Hague Netherlands Radboud Univ Nijmegen Sci Inst Qual Healthcare IQ Healthcare NL-6525 ED Nijmegen Netherlands Erasmus MC Dept Epidemiol Rotterdam Netherlands Erasmus MC Dept Internal Med Rotterdam Netherlands Erasmus MC Dept Med Informat Rotterdam Netherlands Inspectorate Hlth Care The Hague Netherlands Star Med Diagnost Ctr Rotterdam Netherlands Leiden Univ Dept Clin Pharm & Toxicol Med Ctr Leiden Netherlands Leiden Univ Med Ctr Dept Med Stat & Bioinformat Leiden Netherlands Leiden Univ Dept Clin Epidemiol Med Ctr Leiden Netherlands Leiden Univ Dept Thrombosis & Hemostasis Med Ctr Leiden Netherlands Med Diagnost Labs Hoofddorp Netherlands Erasmus MC Dept Hosp Pharm Rotterdam Netherlands

Aim: To evaluate the performance of the European Pharmacogenetics of Anticoagulant Therapy (EU-PACT) acenocoumarol dose algorithms in an independent data set. The EU-PACT trial investigates the added value of pretreatment genotyping for use of warfarin, phenprocoumon and acenocoumarol. Patients & methods: External validation was performed in the Rotterdam Study cohort using information about 707 acenocoumarol users. R-2, which measures the strength of correlation between the predicted and observed acenocoumarol dose, mean absolute error and mean squared error were calculated to evaluate the performance of the original algorithm. Results: Validation resulted in a R-2 of 52.7 and 12.9% compared with an R-2 of 52.6 and 17.8% in the original study for the genotype-guided and nongenotype-guided dose algorithm, respectively. For the genotype-guided dose algorithm, the mean absolute error was 0.48 mg/day and the mean squared error was 0.38 (mg/day)(2). For the nongenotype-guided dose algorithm, the mean absolute error was 0.62 mg/day and the mean squared error was 0.63 (mg/day)2. Conclusion: The EU-PACT acenocoumarol algorithm performs just as accurately in this study as in the original study, which implies applicability in various populations.

关键词： acenocoumarol CYP2C9 dose algorithm validation VKORC1

来源：评论

学校读者我要写书评

暂无评论

Warfarin Pharmacogenetics Reevaluated Subgroup Analysis Reveals a Likely Underestimation of the Maximum Pharmacogenetic Benefit by Clinical Trials

引用

AMERICAN JOURNAL OF CLINICAL PATHOLOGY 2016年第5期145卷 671-686页

作者： Stack, Gary Maurice, Carleta B. VA Connecticut Healthcare Syst Pathol & Lab Med Serv West Haven CT 06516 USA Yale Univ Sch Med Dept Lab Med New Haven CT 06510 USA

Objectives: Various patient subgroups were examined to determine which ones obtain the largest pharmacogenetic improvements in warfarin dose accuracy. Subgrouping schemes of recent clinical trials were analyzed for comparison. Methods: The accuracy of a pharmacogenetic dose algorithm was determined retrospectively in comparison to that of a clinical algorithm in subgroups of the International Warfarin Pharmacogenetics Consortium (IWPC) patient database (n = 2,274) and of newly studied clinic patients (n = 146). Results: White patients with low-dose genotypes (*1*3/AA, *2*2/AA, *2*3/GA, *2*3/AA, *3*3/GG, *3*3/GA, and *3*3/AA) achieved the largest pharmacogenetic improvements in warfarin dose accuracy. Mean absolute dosing error (MAE) in this subgroup of IWPC and newly studied patients was reduced 75.7% and 89.7%, respectively. White IWPC patients with >2 variants or >= 2 mg/day absolute difference between pharmacogenetic and clinical dose predictions obtained MAE reductions of 71.1% and 65.3%, respectively. By comparison, unstratified populations and subgroups of a major clinical trial, when replicated in IWPC patients, obtained smaller MAE reductions of 31.8% to 48.2%. Blacks and Asians obtained substantially smaller dose accuracy improvements overall than whites. Conclusions: Patient subgroups were identified that obtained the largest pharmacogenetic improvements in warfarin dose accuracy. These subgroups have not been analyzed in clinical trials to date, likely resulting in underestimation of the pharmacogenetic benefit.

关键词： Warfarin Oral anticoagulant Pharmacogenetics Genotype CYP2C9 VKORC1 Subgroup dose algorithm

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：