检索结果-内蒙古大学图书馆

An experimental investigation on intra-fractional organ motion effects in lung IMRT treatments

PHYSICS IN MEDICINE AND BIOLOGY 2003年第12期48卷 1773-1784页

作者： Jiang, SB Pope, C Al Jarrah, KM Kung, JH Bortfeld, T Chen, GTY Massachusetts Gen Hosp Dept Radiat Oncol Boston MA 02114 USA Harvard Univ Sch Med Boston MA 02114 USA

Respiration-induced tumour motion can potentially compromise the use of intensity-modulated radiotherapy (IMRT) as a dose escalation tool for lung tumour treatment. We have experimentally investigated the intra-fractional or-an motion effects in lung IMRT treatments delivered by multi-leaf collimator (MLC). An in-house made motor-driven platform, which moves sinusoidally with an amplitude of 1 cm and a period of 4 s, was used to mimic tumour motion. Tumour motion was simulated along cranial-caudal direction while MLC leaves moved across the patient from left to right, as in most clinical cases. The dose to a point near the centre of the tumour mass was measured according to geometric and dosimetric parameters from two five-field lung IMRT plans. For each field, measurement was done for two dose rates (300 and 500 MU min(-1)), three MLC delivery modes (sliding window, step-and-shoot with 10 and 20 intensity levels) and eight equally spaced starting phases of tumour motion. The dose to the measurement point delivered from all five fields was derived for both a single fraction and 30 fractions by randomly sampling from measured dose values of each field at different initial phases. It was found that the mean dose to a moving tumour differs slightly (<2-3%) from that to a static tumour. The variation in breathing phase at the start of dose delivery results in a maximum variation around the mean dose of greater than 30% for one field. The full width at half maximum for the probability distribution of the point dose is up to 8% for all five fields in a single fraction, but less than 1-2% after 30 fractions. In general, lower dose rate can reduce the motion-caused dose variation and therefore might be preferable for lung IMRT when no motion mitigation techniques are used. From the two IMRT cases we studied where tumour motion is perpendicular to MLC leaf motion, the dose variation was found to be insensitive to the MLC delivery mode.

关键词： Motion Lung Organ Delivery experiment 运动(Motion) 肺接生 Lung microprocessor logic circuit Obstetric Delivery initial phase Organ Tumours DOSE RATES MLC1 gene field measure Dose Probability distribution

来源：评论

学校读者我要写书评

暂无评论

Monte Carlo dose calculations for dynamic IMRT treatments

引用

PHYSICS IN MEDICINE AND BIOLOGY 2001年第4期46卷 929-941页

作者： Keall, PJ Siebers, JV Arnfield, M Kim, JO Mohan, R Virginia Commonwealth Univ Med Coll Virginia Hosp Dept Radiat Oncol Richmond VA 23284 USA

Dose calculations for intensity modulated radiation therapy (IMRT) face new challenges due to the complex leaf geometry and time dependent nature of the delivery. A fast method of particle transport through a dynamic multileaf collimator (MLC) geometry that accounts for photon attenuation and first-scattered Compton photon production has been incorporated into an existing Monte Carlo code used for patient dose calculations. Dosimetric agreement between calculation and measurement for two photon energies and MLC types is within experimental error for the sliding window tests. For a patient IMRT field, the Monte Carlo calculations are closer to measured dose than similar superposition or pencil beam calculations.

关键词： Monte Carlo Method Radiometry Radiotherapy Conformal 蒙特卡罗法放射测量术放射疗法适形 sliding windows microprocessor logic circuit arithmetic MONTE-CARLO CALCULATION RADIOMETRY Radiotherapy Monte Carlo technique intensity modulated radiation therapy time-dependent MLC1 gene conformal

来源：评论

学校读者我要写书评

暂无评论

Evaluation of optimization strategies and the effect of initial conditions on IMAT optimization using a leaf position optimization algorithm

引用

PHYSICS IN MEDICINE AND BIOLOGY 2009年第11期54卷 3543-3561页

作者： Oliver, Mike Jensen, Michael Chen, Jeff Wong, Eugene Univ Western Ontario Dept Med Biophys London ON Canada Univ Western Ontario Dept Oncol London ON Canada London Hlth Sci Ctr London Reg Canc Program Dept Phys & Engn London ON Canada Univ Western Ontario Dept Phys & Astron London ON Canada

Intensity-modulated arc therapy (IMAT) is a rotational variant of intensity-modulated radiation therapy (IMRT) that can be implemented with or without angular dose rate variation. The purpose of this study is to assess optimization strategies and initial conditions using a leaf position optimization (LPO) algorithm altered for variable dose rate IMAT. A concave planning target volume (PTV) with a central cylindrical organ at risk (OAR) was used in this study. The initial IMAT arcs were approximated by multiple static beams at 5 degrees angular increments where multi-leaf collimator (MLC) leaf positions were determined from the beam's eye view to irradiate the PTV but avoid the OAR. For the optimization strategy, two arcs with arc ranges of 280 degrees and 150 degrees were employed and plans were created using LPO alone, variable dose rate optimization (VDRO) alone, simultaneous LPO and VDRO and sequential combinations of these strategies. To assess the MLC initialization effect, three single 360 degrees arc plans with different initial MLC configurations were generated using the simultaneous LPO and VDRO. The effect of changing optimization degrees of freedom was investigated by employing 3 degrees, 5 degrees and 10 degrees angular sampling intervals for the two 280 degrees, two 150 degrees and single arc plans using LPO and VDRO. The objective function value, a conformity index, a dose homogeneity index, mean dose to OAR and normal tissues were computed and used to evaluate the treatment plans. This study shows that the best optimization strategy for a concave target is to use simultaneous MLC LPO and VDRO. We found that the optimization result is sensitive to the choice of initial MLC aperture shapes suggesting that an LPO-based IMAT plan may not be able to overcome local minima for this geometry. In conclusion, simultaneous MLC leaf position and VDRO are needed with the most appropriate initial conditions (MLC positions, arc ranges and number of arcs) for IMAT.

关键词： microprocessor logic circuit arc LPO gene MLC1 gene arcs INITIAL CONDITIONS

来源：评论

学校读者我要写书评

暂无评论

Leaf sequencing algorithms for segmented multileaf collimation

引用

PHYSICS IN MEDICINE AND BIOLOGY 2003年第3期48卷 307-324页

作者： Kamath, S Sahni, S Li, J Palta, J Ranka, S Univ Florida Dept Comp & Informat Sci Gainesville FL 32611 USA Univ Florida Dept Radiat Oncol Gainesville FL USA

The delivery of intensity-modulated radiation therapy (IMRT) with a multileaf collimator (MLC) requires the conversion of a radiation fluence map into a leaf sequence file that controls the movement of the MLC during radiation delivery. It is imperative that the fluence map delivered using the leaf sequence file is as close as possible to the fluence map generated by the dose optimization algorithm, while satisfying hardware constraints of the delivery system. Optimization of the leaf sequencing algorithm has been the subject of several recent investigations. In this work, we present a systematic study of the optimization of leaf sequencing algorithms for segmental multileaf collimator beam delivery and provide rigorous mathematical proofs of optimized leaf sequence settings in terms of monitor unit (MU) efficiency under most common leaf movement constraints that include minimum leaf separation constraint and leaf interdigitation constraint. Our analytical analysis shows that leaf sequencing based on unidirectional movement of the MLC leaves is as MU efficient as bidirectional movement of the MLC leaves.

关键词： Plant Leaves Algorithms Delivery Maps 植物叶算法接生地图 microprocessor logic circuit Optimization algorithms algorithms MLC1 gene Multileaf collimator fluence foliage maps Analyses, Sequence Obstetric Delivery

来源：评论

学校读者我要写书评

暂无评论

A dosimetric comparison of various multileaf collimators

引用

PHYSICS IN MEDICINE AND BIOLOGY 2002年第12期47卷 N159-N170页

作者： Huq, MS Das, IJ Steinberg, T Galvin, JM Thomas Jefferson Univ Jefferson Med Coll Kimmel Canc Ctr Dept Radiat Oncol Philadelphia PA 19107 USA Univ Penn Dept Radiat Oncol Philadelphia PA 19104 USA Siemens Med Syst Inc Oncol Care Syst Grp Concord CA 94520 USA

The dosimetric characteristics of three niultileaf collimator (MLC) systems (Elekta, Siemens and Varian) having 10 mm leaf width are compared. A 6 MV photon beam was used from each unit for measurements. Film dosimetry was performed for the measurements and the analysis techniques were exactly duplicated in each system. Two of the collimators have rounded leaf ends (Elekta and Varian) and the third (Siemens) has a flat end that follows beam divergence. A scanning densitometer (Wellhofer with 0.45 mm spot and 0.5 mm step size) was used for film analysis. The dosimetric characteristics studied include: penumbra width (80-20%,) as a function of position of the leaf end in the field, inter- and intra-leaf radiation leakage, dose distribution of the tongue and groove, and isodose curves for stepped leaves forming 45degrees angle beam edge. Results show that MLC designs with divergent and non-divergent leaves produce penumbra (80-20%) widths that are within 2.0 mm of each other. However, the distance of the collimator from the x-ray tat-get plays an important role, and the smallest penumbra width was noted for the Varian MLC despite its rounded leaf-end design. Compared to the other systems, this collimator is positioned about 15 cm closer to the patient which affects the skin dose. The MLC with flat leaf end, although closer to the target, showed slightly poorer penumbra width. Inter-leaf leakage through the leaves is 1.3% for two of the collimators (Elekta and Varian) with the backup jaws and is nearly 1%, for the third system (Siemens). The Siemens MLC produces reduced tongue-and-groove effect compared to the other two collimators (Elekta and Varian). The isodose undulation for a stopped edge is found to be significant for the collimator closest to the patient (Varian) and does not depend on the leaf-end shape. There is no perfect MLC system that can be recommended, rather each one has unique advantages and disadvantages that should be weighed with comfort, ease and co

关键词： microprocessor logic circuit collimators film analysis foliage flat-end step size beam divergence penumbra MLC1 gene TSPAN33 gene

来源：评论

学校读者我要写书评

暂无评论

Reducing the number of segments in unidirectional MLC segmentations

引用

PHYSICS IN MEDICINE AND BIOLOGY 2010年第3期55卷 N75-N85页

作者： Mellado, X. Cruz, S. Artacho, J. M. Canellas, M. Univ Zaragoza Aragon Inst Engn Res 13A GTC Zaragoza 50018 Spain Hosp Clin Univ Lozano Blesa Phys & Radiol Protect Serv Zaragoza 50009 Spain

In intensity-modulated radiation therapy (IMRT), fluence matrices obtained from a treatment planning system are usually delivered by a linear accelerator equipped with a multileaf collimator (MLC). A segmentation method is needed for decomposing these fluence matrices into segments suitable for the MLC, and the number of segments used is an important factor for treatment time. In this work, an algorithm for reduction of the number of segments (NS) is presented for unidirectional segmentations, where there is no backtracking of the MLC leaves. It uses a geometrical representation of the segmentation output for searching the key values in a fluence matrix that complicate its decomposition. The NS reduction is achieved by performing minor modifications in these values, under the conditions of avoiding substantial modifications of the dose volume histogram, and does not increase in average the total number of monitor units delivered. The proposed method was tested using two clinical cases planned with the PCRT 3D (R) treatment planning system.

关键词： microprocessor logic circuit Segments fluence Linear accelerators matrices Monitor Device Component reduction index Backtracking MLC1 gene

来源：评论

学校读者我要写书评

暂无评论

A variable fluence step clustering and segmentation algorithm for step and shoot IMRT

引用

PHYSICS IN MEDICINE AND BIOLOGY 2001年第7期46卷 1997-2007页

作者： Bär, W Alber, M Nüsslin, F Univ Tubingen Radiol Klin Abt Med Phys D-72026 Tubingen Germany

A step and shoot sequencer was developed that can be integrated into an IMRT optimization algorithm. The method uses non-uniform fluence steps and is adopted to the constraints of an MLC. It consists of a clustering, a smoothing and a segmentation routine. The performance of the algorithm is demonstrated for eight mathematical profiles of differing complexity and two optimized profiles of a clinical prostate case. The results in terms of stability, flexibility, speed and conformity fulfil the criteria for the integration into the optimization concept. The performance of the clustering routine is compared with another previously published one (Bortfeld et al 1994 Int. J. Radiat. oncol. Biot Phys. 28 723-30) and yields slightly better results in terms of mean and maximum deviation between the optimized and the clustered profile. We discuss the specific attributes of the algorithm concerning its integration into the optimization concept.

关键词： Cluster Analysis Anatomical segmentation Algorithms 聚类分析算法 microprocessor logic circuit DNA Integration fluence Steps algorithms maximum error MLC1 gene Cluster Analysis

来源：评论

学校读者我要写书评

暂无评论

Optimizing the indexing of a resolution-enhancing tertiary collimator for radiotherapy

引用

PHYSICS IN MEDICINE AND BIOLOGY 2001年第12期46卷 N263-N268页

作者： Cooper, P MacKay, RI Williams, PC Christie Hosp NHS Trust NW Med Phys Manchester M20 4BX Lancs England

A method for improving the resolution of multileaf collimator (MLC) defined radiotherapy fields using a tertiary, slotted grid collimator has been investigated and developed further. The original concept was for each slot to be aligned with each leaf pair of opposing MLC leaves. The total treated area is composed of a series of sub-fields, a pattern of irradiated strips, with the width of each strip defined by the width of the slot and the length by the relative separation of the MLC leaf pair. To complete the field, the patient must be indexed relative to the collimator, with the number of sub-fields required determined by the width of the slots and the spacing between them. Two methods were considered by which this indexing could be achieved: movement of the patient while holding the tertiary collimator fixed, or rotating the grid with the point of rotation defined as the radiation source. Consideration of the movement resolution and precision required for the patient support system for non-cardinal gantry, collimator and table angles cast doubt on the practicality of the use of such a strategy. To assess the effect of divergence on the abutting sub-fields, measurements were also performed to assess the uniformity of single fields generated by the tertiary collimator in planes above and below the isocentre using both methods of indexing. As expected, rotation of the collimator resulted in a similar degree of non-uniformity for any plane chosen, whereas significant dose heterogeneities were introduced to treatment planes within 5 cm above and below the isocentre if the patient support system was used. Therefore, the rotation strategy will be implemented with all future versions of the device.

关键词： microprocessor logic circuit collimators Indexing rotation Radiotherapy Ribbon Device Component Tertiary plane MLC1 gene SLOT Resolving power

来源：评论

学校读者我要写书评

暂无评论

Four-dimensional IMRT treatment planning using a DMLC motion-tracking algorithm

引用

PHYSICS IN MEDICINE AND BIOLOGY 2009年第12期54卷 3821-3835页

作者： Suh, Yelin Sawant, Amit Venkat, Raghu Keall, Paul J. Virginia Commonwealth Univ Dept Radiat Oncol Richmond VA 23284 USA Stanford Univ Dept Radiat Oncol Stanford CA 94305 USA

The purpose of this study is to develop a four-dimensional (4D) intensity-modulated radiation therapy (IMRT) treatment-planning method by modifying and applying a dynamic multileaf collimator (DMLC) motion-tracking algorithm. The 4D radiotherapy treatment scenario investigated is to obtain a 4D treatment plan based on a 4D computed tomography (CT) planning scan and to have the delivery flexible enough to account for changes in tumor position during treatment delivery. For each of 4D CT planning scans from 12 lung cancer patients, a reference phase plan was created;with its MLC leaf positions and three-dimensional (3D) tumor motion, the DMLC motion-tracking algorithm generated MLC leaf sequences for the plans of other respiratory phases. Then, a deformable dose-summed 4D plan was created by merging the leaf sequences of individual phase plans. Individual phase plans, as well as the deformable dose-summed 4D plan, are similar for each patient, indicating that this method is dosimetrically robust to the variations of fractional time spent in respiratory phases on a given 4D CT planning scan. The 4D IMRT treatment-planning method utilizing the DMLC motion-tracking algorithm explicitly accounts for 3D tumor motion and thus hysteresis and nonlinear motion, and is deliverable on a linear accelerator.

关键词： microprocessor logic circuit treatment planning Four-Dimensional Computed Tomography Linear accelerators Planning four-dimensional MLC1 gene

来源：评论

学校读者我要写书评

暂无评论

Monte Carlo simulation of a dynamic MLC based on a multiple source model

引用

PHYSICS IN MEDICINE AND BIOLOGY 2001年第12期46卷 3241-3257页

作者： Fix, MK Manser, P Born, EJ Mini, R Rüegsegger, P Univ Zurich Inst Biomed Engn CH-8044 Zurich Switzerland Swiss Fed Inst Technol ETH CH-8044 Zurich Switzerland Univ Bern Inselspital Clin RadioOncol Div Med Radiat Phys CH-3045 Bern Switzerland

Detailed knowledge of the characteristics of the radiation field shaped by a multileaf collimator (MLC) is essential in intensity modulated radiotherapy (IMRT). A previously developed multiple source model (MSM) for a 6 MV beam was extended to a 15 MV beam and supplemented with an accurate model of an 80-leaf dynamic MLC. Using the supplemented MSM and the MC code GEANT, lateral dose distributions were calculated in a water phantom and a portal water phantom, A field which is normally used for the validation of the step and shoot technique and a field from a realistic IMRT treatment plan delivered with dynamic MLC are investigated. To assess possible spectral changes caused by the modulation of beam intensity by an MLC, the energy spectra in five portal planes were calculated for moving slits of different widths. The extension of the MSM to 15 MV was validated by analysing energy fluences, depth doses and dose profiles. In addition, the MC-calculated primary energy spectrum was verified with an energy spectrum which was reconstructed from transmission measurements. NIC-calculated dose profiles using the MSM for the step and shoot case and for the dynamic MLC case are in very good agreement with the measured data from film dosimetry. The investigation of a 13 cm wide field shows an increase in mean photon energy of up to 16% for the 0.25 cm slit compared to the open beam for 6 MV and of up to 6% for 15 MV, respectively. In conclusion, the MSM supplemented with the dynamic MLC has proven to be a powerful tool for investigational and benchmarking purposes or even for dose calculations in IMRT.

关键词： microprocessor logic circuit radiation depth dose treatment planning RADIATION FIELD Film Dosimetry Steps RADIATION DOSE DISTRIBUTIONS MSM MLC1 gene beam intensity energy spectra

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：