Abstract:
:A simple approach was developed that calculates the output factors and tissue maximum ratio of an asymmetric field at any point within the open field, and specifically both at the central axis (when the jaws do not shadow it) and at the effective center of the open field, using the existing tables for symmetric fields and the multidepth profile information for the largest available field size (either open or with a wedge present). Day's method was adapted to calculate the effective values of the usual field-size-dependent parameters. This approach makes these parameters also dependent on the location of the calculation point relative to the field edges in an asymmetric field. This algorithm was tested by comparing its predictions with measurements of asymmetric and half blocked fields, with and without wedges, in a water phantom at different depths and off-axis distances. The agreement between calculated and measured dose rate is within 1%-3% even in highly asymmetric fields for both 6- and 18-MV photons.
journal_name
Med Physjournal_title
Medical physicsauthors
Rosenberg I,Chu JC,Saxena Vdoi
10.1118/1.597524subject
Has Abstractpub_date
1995-01-01 00:00:00pages
55-61issue
1eissn
0094-2405issn
2473-4209journal_volume
22pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract:PURPOSE:Intensity modulated proton therapy (IMPT) is sensitive to errors, mainly due to high stopping power dependency and steep beam dose gradients. Conventional margins are often insufficient to ensure robustness of treatment plans. In this article, a method is developed that takes the uncertainties into account duri...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3556559
更新日期:2011-03-01 00:00:00
abstract::A proton beam is extracted from the 200-MeV linear accelerator at the Fermi National Accelerator Laboratory to investigate the efficacy of proton radiography in medical diagnosis. Fluence rates from 2 X 10(3) to 2 X 10(5) protons/cm2s over a 28-cm diameter field are obtained with a full width at half-maximum beam-ener...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594426
更新日期:1978-05-01 00:00:00
abstract:PURPOSE:Many biological objects, including neuronal dendrites, blood vasculature, airways, phylogenetic trees, produce tree structured data. Current methods of analysis either ignore the complex structure of trees or use distance-based methods which limit the scope of multivariate modeling. METHODS:We propose a branch...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12751
更新日期:2018-03-01 00:00:00
abstract:PURPOSE:To apply the recent code of practice from the IAEA/AAPM, TRS 483, to helical tomotherapy (HT) for reference and relative dosimetry obtaining correction factors for the Exradin A1SL ionization chamber. METHODS:The beam quality correction factor for the A1SL chamber was obtained through three different approache...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13855
更新日期:2019-12-01 00:00:00
abstract:PURPOSE:Automated detection of solitary pulmonary nodules using positron emission tomography (PET) and computed tomography (CT) images shows good sensitivity; however, it is difficult to detect nodules in contact with normal organs, and additional efforts are needed so that the number of false positives (FPs) can be fu...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4948498
更新日期:2016-06-01 00:00:00
abstract:PURPOSE:Current treatment planning for 90 Y radioembolization estimates lung mean dose (LMD) by measuring the lung shunt fraction (LSF) from 99m Tc-macroaggregated albumin (MAA) planar imaging and assuming a 1-kg lung mass. This methodology, however, overestimates LSF and LMD and could therefore unnecessarily limit the...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13575
更新日期:2019-09-01 00:00:00
abstract:PURPOSE:The purpose of this study is to investigate some characteristics of the beam delivery system and their effects on the dose distribution of intensity-modulated radiation therapy (IMRT) and the results of patient-specific IMRT quality assurance (QA). These characteristics include the accelerator source distributi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3413997
更新日期:2010-06-01 00:00:00
abstract:PURPOSE:Osteoporosis is a common bone disease associated with increased risk of low-trauma fractures leading to substantial morbidity, mortality, and financial costs. Clinically, osteoporosis is defined by low bone mineral density (BMD); however, increasing evidence suggests that trabecular bone (TB) microarchitectural...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4928481
更新日期:2015-09-01 00:00:00
abstract:PURPOSE:The automated correct segmentation of left and right lungs is a nontrivial problem, because the tissue layer between both lungs can be quite thin. In the case of lung segmentation with left and right lung models, overlapping segmentations can occur. In this paper, the authors address this issue and propose a so...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4894817
更新日期:2014-10-01 00:00:00
abstract:PURPOSE:The authors are developing a system for calibrated breast density measurements using full field digital mammography (FFDM). Breast tissue equivalent (BTE) phantom images are used to establish baseline (BL) calibration curves at time zero. For a given FFDM unit, the full BL dataset is comprised of approximately ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4903299
更新日期:2015-02-01 00:00:00
abstract:PURPOSE:The aim of this study is to investigate the performance of Sentinel(™), a patient setup verification device based on a laser/camera system, when used on rigid-body phantoms. METHODS:The Sentinel system consists of a scanner unit, containing the laser and the camera, and surface-matching registration software. ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3675973
更新日期:2012-02-01 00:00:00
abstract::The implementation of an improved model for multiple scattering into the-Voxel Monte Carlo (VMC) algorithm for fast electron dose calculation in radiation therapy is presented. The model takes into account path-length corrections (PLC) and lateral displacement in the individual electron steps. The extraction of the sc...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597933
更新日期:1997-04-01 00:00:00
abstract:PURPOSE:It is very important for calculation of clinical indices and diagnosis to detect thyroid nodules from ultrasound images. However, this task is a challenge mainly due to heterogeneous thyroid nodules with distinct components are similar to background in ultrasound images. In this study, we employ cascade deep co...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12134
更新日期:2017-05-01 00:00:00
abstract::We believe that, for the purpose of evaluation and optimization of treatment plans, quasirandom sampling is superior to grid sampling and should be the method of choice. We believe it to be on average more efficient than grid sampling (i.e., more accurate for any given number of dose estimates) and, even more importan...
journal_title:Medical physics
pub_type: 评论,信件
doi:10.1118/1.597103
更新日期:1993-09-01 00:00:00
abstract::We are investigating computerized methods to ultimately characterize bone trabecular pattern from clinical skeletal radiographs. In this paper, we present a "phantom" for potential use in the development and evaluation of computerized methods for characterizing radiographic trabecular patterns and ultimately bone stre...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598743
更新日期:1999-11-01 00:00:00
abstract::Because of the high energy of the treatment beam, contrast of portal verification films is very poor. A simple contrast enhancement technique is described which we have labeled selective histogram equalization (SHE), to improve visualization of double-exposure portal images and this facilitate the beam verification pr...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597085
更新日期:1993-01-01 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::The modulation transfer function (MTF) and the noise power spectrum (NPS) are widely recognized as the most relevant metrics of resolution and noise performance in radiographic imaging. These quantities have commonly been measured using various techniques, the specifics of which can have a bearing on the accuracy of t...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2188816
更新日期:2006-05-01 00:00:00
abstract::Errors in the determination of xenon concentrations in arterial blood during inhalation of xenon-oxygen mixtures are used to assess errors in the derivation of regional cerebral blood flow by the xenon-enhanced computed tomography (CT) method. The results of this study indicate that approximating the arterial buildup ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596051
更新日期:1987-05-01 00:00:00
abstract::Depth dose distributions for a d(14)Be neutron beam, measured separately for total and gamma absorbed dose, are presented for nine tissue substitutes and for two field sizes. These data are used to examine methods to transform depth dose curves from one material to another. Best results are found when the local depths...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595695
更新日期:1985-05-01 00:00:00
abstract::The GEANT4 application for tomographic emission (GATE) is one of the most detailed Monte Carlo simulation tools for SPECT and PET. It allows for realistic phantoms, complex decay schemes, and a large variety of detector geometries. However, only a fraction of the information in each particle history is available for p...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3078045
更新日期:2009-04-01 00:00:00
abstract:PURPOSE:The Imaging and Radiation Oncology Core Houston (IROC-H) (formerly the Radiological Physics Center) has reported varying levels of agreement in their anthropomorphic phantom audits. There is reason to believe one source of error in this observed disagreement is the accuracy of the dose calculation algorithms an...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12426
更新日期:2017-09-01 00:00:00
abstract::A method for finding optimal primary fluence profiles for multiple field external beam radiation therapy techniques has been developed using a radiobiologically based objective function that quantifies the probability of achieving complication-free tumor control, P+. The objective function P+ has the valuable property...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596971
更新日期:1993-07-01 00:00:00
abstract::Modern linear accelerators contain multiple isocentres, defined by the mechanical motions of gantry, collimator and table. Isocentre localization for these motions has been performed using film and manual evaluations which have difficulty in relating the individual motions. To address these limitations, we have develo...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2965950
更新日期:2008-07-01 00:00:00
abstract:PURPOSE:To investigate the effect of energy (kVp) and filters (no filter, half Bowtie, and full Bowtie) on the dose response curves of the Gafchromic XRQA2 film and nanoDot optical stimulated luminescence dosimeters (OSLDs) in CBCT dose fields. To measure surface and internal doses received during x-ray volume imager (...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4803466
更新日期:2013-06-01 00:00:00
abstract:PURPOSE:To develop a real time dose monitoring and dose reconstruction tool to identify and quantify sources of errors during patient specific volumetric modulated arc therapy (VMAT) delivery and quality assurance. METHODS:The authors develop a VMAT delivery monitor tool called linac data monitor that connects to the ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4764482
更新日期:2012-12-01 00:00:00
abstract:PURPOSE:Alpha-emitting radionuclides exhibit a potential advantage for cancer treatments because they release large amounts of ionizing energy over a few cell diameters (50-80 μm), causing localized, irreparable double-strand DNA breaks that lead to cell death. Radioimmunotherapy (RIT) approaches using monoclonal antib...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4921997
更新日期:2015-07-01 00:00:00
abstract::A test device which can indirectly measure the performance of an automatic exposure control system and which offers the potential to reduce the time and film requirements for such tests has been evaluated. Evaluation results demonstrate that the device can successfully predict image optical density to within +/- 0.10 ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597252
更新日期:1994-01-01 00:00:00
abstract::We present a technique for semiautomated segmentation of human prostates using suprapubic ultrasound (US) images. In this approach, a speckle reducing anisotropic diffusion (SRAD) is applied to enhance the images and the instantaneous coefficient of variation (ICOV) is utilized for edge detection. Segmentation is acco...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1809791
更新日期:2004-12-01 00:00:00
abstract:PURPOSE:An optimized air ventilation system design for a treatment room in Heavy-ion Medical Facility is an important issue in the aspects of nuclear safety because the activated air produced in a treatment room can directly affect the medical staff and the general public in the radiation-free area. METHODS:Optimized ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12914
更新日期:2018-06-01 00:00:00