Abstract:
PURPOSE:Cone beam computed tomography (CBCT) image quality suffers from contamination from scattered photons in the projection images. Monte Carlo simulations are a powerful tool to investigate the properties of scattered photons.egs_cbct, a recent EGSnrc user code, provides the ability of performing fast scatter calculations in CBCT projection images. This paper investigates how optimization of user inputs can provide the most efficient scatter calculations. METHODS:Two simulation geometries with two different x-ray sources were simulated, while the user input parameters for the efficiency improving techniques (EITs) implemented inegs_cbct were varied. Simulation efficiencies were compared to analog simulations performed without using any EITs. Resulting scatter distributions were confirmed unbiased against the analog simulations. RESULTS:The optimal EIT parameter selection depends on the simulation geometry and x-ray source. Forced detection improved the scatter calculation efficiency by 80%. Delta transport improved calculation efficiency by a further 34%, while particle splitting combined with Russian roulette improved the efficiency by a factor of 45 or more. Combining these variance reduction techniques with a built-in denoising algorithm, efficiency improvements of 4 orders of magnitude were achieved. CONCLUSIONS:Using the built-in EITs inegs_cbct can improve scatter calculation efficiencies by more than 4 orders of magnitude. To achieve this, the user must optimize the input parameters to the specific simulation geometry. Realizing the full potential of the denoising algorithm requires keeping the statistical uncertainty below a threshold value above which the efficiency drops exponentially.
journal_name
Med Physjournal_title
Medical physicsauthors
Thing RS,Mainegra-Hing Edoi
10.1118/1.4881142subject
Has Abstractpub_date
2014-07-01 00:00:00pages
071902issue
7eissn
0094-2405issn
2473-4209journal_volume
41pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract::In patients with lymphoma, identification and quantification of the tumor extent on serial CT examinations is critical for assessing tumor response to therapy. In this paper, we present a computer method to automatically match and segment lymphomas in follow-up CT images. The method requires that target lymph nodes in...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2404617
更新日期:2007-01-01 00:00:00
abstract:PURPOSE:This study aims to investigate the feasibility of using the images of the treatment fields acquired by an electronic portal imaging device (EPID) for real-time target localization. METHODS:Forty one patients treated with IMRT and RapidArc were recruited in this study including 37 prostate patients and 4 lung p...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4734975
更新日期:2012-06-01 00:00:00
abstract::Deformable image registration is an important tool for image-guided radiotherapy. Physics-model-based deformable image registration using finite element analysis is one of the methods currently being investigated. The calculation accuracy of finite element analysis is dependent on given boundary conditions, which are ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1774131
更新日期:2004-09-01 00:00:00
abstract:PURPOSE:For accurate tissue inhomogeneity correction in radiotherapy treatment planning, the authors had previously proposed a novel conversion of the energy-subtracted CT number to an electron density (ΔHU-ρe conversion), which provides a single linear relationship between ΔHU and ρe over a wide ρe range. The purpose ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4881327
更新日期:2014-07-01 00:00:00
abstract:PURPOSE:Stereotactic body radiation therapy (SBRT) is a radiotherapy technique which uses high dose fractions with multiple coplanar and noncoplanar beams. Due to the large fractional doses, treatments are typically protracted and there are more fields than in conventional radiation treatment schemes. The effect of tem...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4709605
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:A critical step in adaptive radiotherapy (ART) workflow is deformably registering the simulation CT with the daily or weekly volumetric imaging. Quantifying the deformable image registration accuracy under these circumstances is a complex task due to the lack of known ground-truth landmark correspondences betwe...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12321
更新日期:2017-08-01 00:00:00
abstract::The purpose of this study was to investigate if interfraction and intrafraction motion in free-breathing and gated lung IMRT can lead to systematic dose differences between 3DCT and 4DCT. Dosimetric effects were studied considering the breathing pattern of three patients monitored during the course of their treatment ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2821704
更新日期:2008-01-01 00:00:00
abstract:PURPOSE:Positron emission tomography (PET) is considered the gold standard for measuring myocardial blood flow in vivo but it is known that respiratory motion can lead to misalignment of the PET and computed tomography (CT) data sets and introduce artifacts in the CT-based attenuation correction (AC) of images. In addi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4788669
更新日期:2013-02-01 00:00:00
abstract::Radiographic image guidance has emerged as the new paradigm for patient positioning, target localization, and external beam alignment in radiotherapy. Although widely varied in modality and method, all radiographic guidance techniques have one thing in common--they can give a significant radiation dose to the patient....
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2775667
更新日期:2007-10-01 00:00:00
abstract::In this work, we present a calcification-detection scheme that automatically localizes calcifications in a previously detected cluster in order to generate the input for a cluster-classification scheme developed in the past. The calcification-detection scheme makes use of three pieces of a priori information: the loca...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1559884
更新日期:2003-05-01 00:00:00
abstract::AAPM Magnetic Resonance Task Group #9 on proton magnetic resonance spectroscopy (MRS) in the brain was formed to provide a reference document for acquiring and processing proton (1H) MRS acquired from brain tissue. MRS is becoming a common adjunct to magnetic resonance imaging (MRI), especially for the differential di...
journal_title:Medical physics
pub_type: 指南,杂志文章,实务指引,评审
doi:10.1118/1.1501822
更新日期:2002-09-01 00:00:00
abstract::A new rubber band straightening transform (RBST) is introduced for characterization of mammographic masses as malignant or benign. The RBST transforms a band of pixels surrounding a segmented mass onto the Cartesian plane (the RBST image). The border of a mammographic mass appears approximately as a horizontal line, a...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598228
更新日期:1998-04-01 00:00:00
abstract:PURPOSE:Pulse pileup occurring at high x-ray fluxes can severely degrade the energy resolution provided by a photon counting detector, which can represent a problem in spectroscopic CT when performing quantitative material discrimination tasks. As the effects of pileup can be most easily seen as a degradation of a dete...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4820535
更新日期:2013-10-01 00:00:00
abstract::A slat collimator in single photon emission computed tomography consists of a set of parallel slats. As the collimator spins, the detector measures a one-dimensional projection data set. A complete data set can be obtained by rotating the detector/collimator assembly around the object (patient) while the collimator sp...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1485057
更新日期:2002-07-01 00:00:00
abstract:PURPOSE:The biologically effective dose (BED) of temporary brachytherapy treatments is a function of both chosen radionuclide (R) and implant duration (T). This study endeavored to evaluate BED delivered to the tumor volume and surrounding ocular structures as a function of plaque position (P), prescription dose, R, an...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4735548
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:Intensity modulated proton therapy (IMPT) of head and neck (H&N) cancer patients may be improved by plan adaptation. The decision to adapt the treatment plan based on a dose recalculation on the current anatomy requires a diagnostic quality computed tomography (CT) scan of the patient. As gantry-mounted cone be...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4908223
更新日期:2015-03-01 00:00:00
abstract::With intensity-modulated radiotherapy (IMRT), a variety of user-defined dose distribution can be produced using inverse planning. The generalized equivalent uniform dose (gEUD) has been used in IMRT optimization as an alternative objective function to the conventional dose-volume-based criteria. The purpose of this st...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1897464
更新日期:2005-05-01 00:00:00
abstract::Patient-specific intensity-modulated radiotherapy (IMRT) verifications require an accurate two-dimensional dosimeter that is not labor-intensive. We assessed the precision and reproducibility of film calibrations over time, measured the elemental composition of the film, measured the intermittency effect, and measured...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1852791
更新日期:2005-02-01 00:00:00
abstract::A simple modification is presented for two commercially available hyperthermia applicators which dramatically improves the regulation and dynamic control of the temperature at the bolus/tissue interface. This alteration requires the addition of a variable speed pump, bubble trap, simple heat exchanger, and a few minor...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597196
更新日期:1994-09-01 00:00:00
abstract:PURPOSE:Measured values of ultrasound attenuation in bone represent a combination of different loss mechanisms. As a wave is transmitted from a fluid into bone, reflections occur at the interface. In the bone, mode conversion occurs between longitudinal and shear modes and the mechanical wave is scattered by its comple...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3668316
更新日期:2012-01-01 00:00:00
abstract::Modern radiotherapy linacs often use carbon fibre for their couch tops due to its radio translucent properties. Beam attenuation by the couches is often ignored during planning and MU calculation. This work examines beam attenuation and loss of "skin sparing" (dose build up region) when various photon beams transit ei...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2965951
更新日期:2008-07-01 00:00:00
abstract:PURPOSE:Concurrent irradiation of the prostate and pelvic lymph nodes is technically challenging due to treating one moving target and one immobile target. The purposes of this article are to propose a new management strategy and to compare this strategy to the conventional isocenter shift method and the previously pro...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3480505
更新日期:2010-09-01 00:00:00
abstract:PURPOSE:A radiophotoluminescent glass rod dosimeter (RGD) has recently become commercially available. It is being increasingly used for dosimetry in radiotherapy to measure the absorbed dose including scattered low-energy photons on the body surface of a patient and for postal dosimetry audit. In this article, the dosi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4747261
更新日期:2012-10-01 00:00:00
abstract::In this study, we present an algorithm for three-dimensional (3-D) dose reconstruction using portal images obtained with an electronic portal imaging device (EPID). For this purpose an algorithm for 2-D dose reconstruction, which was previously developed in our institution, was adapted. The external contour of the pat...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1589496
更新日期:2003-09-01 00:00:00
abstract:PURPOSE:The local depth dose gradient and the displacement correction factor for Farmer-type ionization chambers are quantified for reference dosimetry at shallow depth in single-layer scanned proton fields. METHOD:Integrated radial profiles as a function of depth (IRPDs) measured at three proton therapy centers were ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14554
更新日期:2020-12-01 00:00:00
abstract::Stereotactic Body Radiation Therapy (SBRT) is an important form of cancer therapy with increasingly broad application across a spectrum of tumor types in primary and metastatic settings. In this presentation the radiation biology, clinical experience from various trials, and cautionary updates on normal tissue toleran...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4735812
更新日期:2012-06-01 00:00:00
abstract::Surgical guidance with fluorescence has been demonstrated in individual clinical trials for decades, but the scientific and commercial conditions exist today for a dramatic increase in clinical value. In the past decade, increased use of indocyanine green based visualization of vascular flow, biliary function, and tis...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4951732
更新日期:2016-06-01 00:00:00
abstract:PURPOSE:Stereotactic ablative body radiotherapy (SABR) for lung patients can be performed with volumetric-modulated arc therapy (VMAT) plans using off-axis target geometry to allow treatment in their CBCT verified position. For patient-specific quality assurance measurements using the PTW Octavius 4D phantom (PTW, Frei...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12805
更新日期:2018-04-01 00:00:00
abstract:PURPOSE:In breast radiotherapy with intensity modulation, it is a well established practice to extend the dose fluence outside the limit of the body contour to account for small changes in size and position of the target and the rest of the tissues due to respiration or to possible oedema. A simple approach is not appl...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3598442
更新日期:2011-07-01 00:00:00
abstract::Multimodality NIR spectroscopy systems offer the possibility of region-based vascular and molecular characterization of tissue in vivo. However, computationally efficient 3D image reconstruction algorithms specific to these image-guided systems currently do not exist. Image reconstruction is often based on finite-elem...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2795832
更新日期:2007-11-01 00:00:00