Abstract:
:Electron-beam characteristics of a Philips SL25 linear accelerator have been studied. Central-axis percentage depth doses, cross-beam profiles and beam output factors of 6-, 10-, and 20-MeV beams, selected from the available energy range of 4 to 22 MeV, are reported in this paper. The main thrust of this work is to determine the systematic variation of beam characteristics, especially the output factor, with standard cone sizes and cerrobend beam-shaping cutouts down to a field size of 2 X 2 cm Output factors for the standard cones (open field) are energy dependent in a complex manner, increasing with the cone size for the 6-MeV beam whereas decreasing for 10- and 20-MeV beams. The output factor falls below unity at lower energies (6 and 10 MeV) for fields with at least one side smaller than 6 cm, and stays nearly constant for the 20-MeV beam. Measured output factors of small fields are least squares fitted by a second-order polynomial function. Output factors for small rectangular fields have been derived from the one-dimensional and square-root formulas, and the equivalent-square method. Only the one-dimensional formula predicts the measured output factors of highly elongated fields to within +/- 1% experimental uncertainties. Different cones with the same size electron cutout show a varied dose response, primarily due to variation in scattered electron contamination from the cones.
journal_name
Med Physjournal_title
Medical physicsauthors
Rashid H,Islam MK,Gaballa H,Rosenow UF,Ting JYdoi
10.1118/1.596471subject
Has Abstractpub_date
1990-07-01 00:00:00pages
710-4issue
4eissn
0094-2405issn
2473-4209journal_volume
17pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract:PURPOSE:To develop a real-time markerless 3D tumor tracking using kilovoltage (kV) cone-beam CT (CBCT) projection images during volumetric modulated arc therapy (VMAT) treatment of lung tumors. METHODS:The authors have developed a method to identify the position of lung tumors during VMAT treatment, where the current ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4821545
更新日期:2013-10-01 00:00:00
abstract:PURPOSE:There is evidence that computed tomography (CT) and positron emission tomography (PET) imaging metrics are prognostic and predictive in nonsmall cell lung cancer (NSCLC) treatment outcomes. However, few studies have explored the use of standardized uptake value (SUV)-based image features of nodal regions as pre...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4926755
更新日期:2015-08-01 00:00:00
abstract::The optimum x-ray spectra for acquisition of digital mammographic images using an amorphous selenium (a-Se) photoconductor are investigated. The recorded images consist of latent charge distributions on the surface of an a-Se plate, which are then read out using two methods, laser discharge, or flat panel recharge. Th...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597688
更新日期:1996-04-01 00:00:00
abstract::Intrafraction organ motion can limit the advantage of highly conformal dose techniques such as intensity modulated radiation therapy (IMRT) due to target position uncertainty. To ensure high accuracy in beam targeting, real-time knowledge of the target location is highly desired throughout the beam delivery process. T...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2905225
更新日期:2008-05-01 00:00:00
abstract::The output factor for a therapy photon beam is defined as the dose per monitor unit relative to the dose per monitor unit in a reference field. Convolution models for photon dose calculations yield the dose in units normalized to the incident energy fluence with phantom scatter intrinsically modeled. Output factors ca...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596859
更新日期:1992-03-01 00:00:00
abstract:PURPOSE:Motion compensated positron emission tomography (PET) imaging requires detecting and monitoring of patient body motion. We developed a semiautomatic list-mode method to track the three-dimensional (3D) motion of fiducial positron-emitting markers during PET imaging. METHODS:A previously developed motion tracki...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14206
更新日期:2020-08-01 00:00:00
abstract:PURPOSE:The treatment of thoracic cancer using external beam radiation requires an optimal selection of the radiation beam directions to ensure effective coverage of the target volume and to avoid unnecessary treatment of normal healthy tissues. Intensity modulated radiation therapy (IMRT) planning is a lengthy process...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4908000
更新日期:2015-04-01 00:00:00
abstract::We attempt to select an optimal value of regularization parameter in the optimization problems for intensity-modulated radiotherapy which are solved using a variational regularization technique. We apply to inverse treatment planning the L-curve method which was developed to determine the regularization parameter in t...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1949750
更新日期:2005-08-01 00:00:00
abstract::Neutron and photon energy spectra were measured in different depths and lateral positions in tissue-equivalent phantoms exposed to a therapeutical 14.1 MeV neutron beam. Intensity weighted mass energy absorption coefficients were derived for application in ionization chamber dosimetry in mixed neutron-gamma fields. Th...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594744
更新日期:1980-09-01 00:00:00
abstract::A conceptual design is presented showing that, by judiciously choosing the beryllium target thickness and the backstop material, improvements can be achieved in dose-rate, skin sparing, and penetration of neutron beams generated by the same proton accelerator. ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594748
更新日期:1980-09-01 00:00:00
abstract:PURPOSE:In order to build up a reliable dose monitoring system for boron neutron capture therapy (BNCT) applications at the TRIGA reactor in Mainz, a computer model for the entire reactor was established, simulating the radiation field by means of the Monte Carlo method. The impact of different source definition techni...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4897242
更新日期:2014-11-01 00:00:00
abstract::The scattered-photon part of pencil-beam dose kernels for high-energy x-ray beams can be derived experimentally by differentiating the broad-beam scatter-to-primary dose ratio as a function of radius. Formally, this requires a uniform and parallel beam, and the procedure is complicated by the nonideal, actual beam con...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597884
更新日期:1996-09-01 00:00:00
abstract:PURPOSE:Colon cancer is a major public health problem due to its high disease rate and death toll worldwide. The use of FTIR microscopy in the field of cancer diagnosis has become attractive over the past 20 years. In the present study, the authors investigated the potential of FTIR microscopy to define spectral change...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3298013
更新日期:2010-03-01 00:00:00
abstract:PURPOSE:Stray neutron radiation is of concern after radiation therapy, especially in children, because of the high risk it might carry for secondary cancers. Several previous studies predicted the stray neutron exposure from proton therapy, mostly using Monte Carlo simulations. Promising attempts to develop analytical ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4829512
更新日期:2013-12-01 00:00:00
abstract::The validity of conclusions drawn from multi-institutional radiotherapy studies is dependent upon the degree to which participating hospitals adhere to study requirements. A major effort undertaken by the Quality Assurance Review Center (QARC) assesses whether or not patient data which are deemed evaluable actually co...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595221
更新日期:1982-03-01 00:00:00
abstract:PURPOSE:Tissue textures have been recognized as biomarkers for various clinical tasks. In computed tomography (CT) image reconstruction, it is important but challenging to preserve the texture when lowering x-ray exposure from full- toward low-/ultra-low dose level. Therefore, this paper aims to explore the texture-dos...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14449
更新日期:2020-10-01 00:00:00
abstract:PURPOSE:Scattered radiation remains to be a major cause of image quality degradation in Flat Panel Detector (FPD)-based Cone-beam computed tomography (CBCT). We have been investigating a novel two-dimensional antiscatter grid (2D-ASG) concept to reduce scatter intensity, and hence improve CBCT image quality. We present...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12724
更新日期:2018-02-01 00:00:00
abstract::Limiting spatial resolution is a key metric of the quality of magnetic resonance (MR) images, which can provide an indication of the smallest region that can effectively be imaged. In this paper a novel methodology for measuring the limiting spatial resolution of MR images is mathematically analyzed and successfully i...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3097633
更新日期:2009-05-01 00:00:00
abstract::This study presents experimental results about the effective depth of penetration and about the radiofrequency (rf) power absorption in humans as a function of frequency. The frequency range investigated covers 10 up to 220 MHz. For the main part, the results were derived from bench measurements of the quality factor ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595995
更新日期:1987-11-01 00:00:00
abstract::Methods for scatter dose calculations in brachytherapy have been developed based on the collapsed cone superposition algorithm. The methods account for effects on the scatter dose caused by the three-dimensional distribution of heterogeneities in the irradiated volume and are considerably faster than methods based on ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1290485
更新日期:2000-10-01 00:00:00
abstract::A novel iterative penalized likelihood algorithm with evolutionary components for the optimization of beamlet fluences for intensity modulated radiation therapy (IMRT) is presented. This algorithm is designed to be flexible in terms of the objective function and automatically escalates dose, as long as the objective f...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1773631
更新日期:2004-08-01 00:00:00
abstract::In proton therapy, it is important to evaluate the field irradiated with protons and the deposited dose distribution in a patient's body. Positron emitters generated through fragmentation reactions of target nuclei can be used for this purpose. By detecting the annihilation gamma rays from the positron emitters, the a...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2712572
更新日期:2007-05-01 00:00:00
abstract:PURPOSE:Tumor grading is an important part of breast cancer diagnosis and currently requires biopsy as its standard. Here, the authors investigate quantitative ultrasound parameters in locally advanced breast cancers that can potentially separate tumors from normal breast tissue and differentiate tumor grades. METHODS...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4852875
更新日期:2014-01-01 00:00:00
abstract::Deionized water is commonly used to couple microwave applicators to the patient surface in the administration of local hyperthermia. Profiles of the specific absorption rate (SAR) at 1-cm depth show that deionized water coupling significantly distorts the SAR distributions of the Clini-Therm 915-MHz 10 X 10 and 15 X 1...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595881
更新日期:1986-05-01 00:00:00
abstract:PURPOSE:The aim of this paper was to investigate the relationship between the physical and subjective (observer) image quality metrics in digital chest radiography. METHODS:Five digital radiography systems, four with indirect flat panel detector and one with storage phosphor-based computed radiography system, were use...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14244
更新日期:2020-09-01 00:00:00
abstract:PURPOSE:Measuring and incorporating a scanner-specific point spread function (PSF) within image reconstruction has been shown to improve spatial resolution in PET. However, due to the short half-life of clinically used isotopes, other long-lived isotopes not used in clinical practice are used to perform the PSF measure...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4870985
更新日期:2014-05-01 00:00:00
abstract::Model-based deformable organ registration techniques using the finite element method (FEM) have recently been investigated intensively and applied to image-guided adaptive radiotherapy (IGART). These techniques assume that human organs are linearly elastic material, and their mechanical properties are predetermined. U...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2163838
更新日期:2006-02-01 00:00:00
abstract:PURPOSE:Robust registration of prone and supine colonie surfaces acquired during CT colonography may lead to faster and more accurate detection of colorectal cancer and polyps. Any directional bias when registering one surface to the other could precipitate incorrect anatomical correspondence and engender reader error....
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4736159
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:Because the small-radius photon beams shaped by cones in stereotactic radiosurgery (SRS) lack lateral electronic equilibrium and a detector's finite cross section, direct experimental measurement of dosimetric data for these beams can be subject to large uncertainties. As the dose calculation accuracy of a trea...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3488900
更新日期:2010-10-01 00:00:00
abstract::Using stable materials capable of mimicking any soft tissues of the human body--quantitatively with respect to speed of sound, density, and attenuation coefficient and semiquantitatively with respect to scatter--we have constructed a torso section phantom containing simulated bowel gas, kidney, kidney fat pad, liver, ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594657
更新日期:1980-01-01 00:00:00