Abstract：
:The photon energy spectrum emanating from a Leksell Gamma Knife, Model 23004B, was measured between 0.250 and 3.5 MeV with the sources exposed. Measurements were made using a 2x2 inch NaI detector enclosed in a lead-shielded apparatus having a 1/4 inch diameter measurement aperture, which reduced the amount of radiation received by the crystal. All measurements were made one meter above the floor within a quadrant toward one side of the Gamma Knife couch. The measured spectra displayed the expected 60Co doublet of photon peaks at energies of 1.17 and 1.33 MeV. These peaks appeared in spectra beginning at approximately 50 degrees, as one proceeds from a point directly lateral to the source enclosure (0 degrees) toward the foot of the couch (90 degrees). The average photon energy of the spectrum shifts to lower values as the doublet decreases in magnitude with increasing angle until almost vanishing at an angle equal to 90 degrees. Inserting a 16 cm diameter plastic sphere phantom, provided with the Gamma Knife, into the radiation beams increases the low energy photon emissions appearing in the spectrum, especially for measurements at the foot of the couch. Implications for the design of shielding a treatment room containing the Gamma Knife, Model B, and estimation of the radiation exposure to personnel during an emergency procedure in the treatment room with the sources exposed are discussed.
journal_name
Med Physjournal_title
Medical physicsauthors
Drzymala RE,Sohn JW,Guo C,Sobotka LG,Purdy JAdoi
10.1118/1.1355305subject
Has Abstractpub_date
2001-04-01 00:00:00pages
620-8issue
4eissn
0094-2405issn
2473-4209journal_volume
28pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract：PURPOSE:The quantification of vessel wall morphology and plaque burden requires vessel segmentation, which is generally performed by manual delineations. The purpose of our work is to develop and evaluate a new 3D model-based approach for carotid artery wall segmentation from dual-sequence MRI. METHODS:The proposed me...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1002/mp.12476
更新日期：2017-10-01 00:00:00
abstract：:The purpose of this study was to investigate the effect of z overscanning on eye lens dose and effective dose received by pediatric patients undergoing head CT examinations. A pediatric patient study was carried out to obtain the exposure parameters and data regarding the eye lens position with respect to imaged volum...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.2207212
更新日期：2006-07-01 00:00:00
abstract：:The American Association of Physicists in Medicine recommends that the reference dose-rate distribution, used for treatment planning for low-energy photon brachytherapy sources in routine clinical use, must be based on at least two independent determinations: one using experimentally measured dose rates and one using ...
journal_title：Medical physics
pub_type： 指南,杂志文章
doi：10.1118/1.1690712
更新日期：2004-05-01 00:00:00
abstract：:Traditionally, short scan helical FDK algorithms have been implemented based on horizontal transaxial slices. However, not every point on the horizontal transaxial slice satisfies Tuy's condition for the corresponding (pi+fan angle) segment of helix, which means that some points on the horizontal slices are incomplete...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.1916077
更新日期：2005-06-01 00:00:00
abstract：PURPOSE:Researchers write many computer programs with unique implementations, usually requiring a great amount of effort for other researchers to learn how to install, configure, and use. Some programs require specialized hardware platforms such as GPU workstation or CPU cluster, which may not readily available for man...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.4735274
更新日期：2012-06-01 00:00:00
abstract：PURPOSE:We propose a new method for efficient particle transportation in voxelized geometry for Monte Carlo simulations. We describe its use for calculating dose distribution in CT images for radiation therapy. MATERIAL AND METHODS:The proposed approach, based on an implicit volume representation named segmented volum...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.2884854
更新日期：2008-04-01 00:00:00
abstract：:A beam stop technique was used to measure the densitometric scatter fractions under three regions of a humanoid chest phantom utilizing LaOBr and Gd2O2S screens. For these receptors, the scatter fractions under the lung and retrocardiac areas were 13%-36% lower than published values for CaWO4. In the mediastinal area,...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.597041
更新日期：1993-03-01 00:00:00
abstract：:A beam intensity monitor was tested in a 230-MeV proton beam at the Loma Linda Proton Therapy Accelerator during its commissioning at Fermi National Accelerator Laboratory. The intensity monitor was designed to regulate the beam intensity extracted from the proton synchrotron. The proton beam is tunable between 70 and...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.596636
更新日期：1991-07-01 00:00:00
abstract：PURPOSE:Most clinically deployed strategies for respiratory motion management in lung radiotherapy (e.g., gating and tracking) use external markers that serve as surrogates for tumor motion. However, typical lung phantoms used to validate these strategies are based on a rigid exterior and a rigid or a deformable-interi...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.4918581
更新日期：2015-05-01 00:00:00
abstract：PURPOSE:The appearance of parenchymal∕stromal patterns in mammography have been characterized as having a Wiener power spectrum with an inverse power-law shape described by the exponential parameter, β. The amount of fibroglandular tissue, which can be quantified in terms of volumetric breast density (VBD), influences ...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.4736422
更新日期：2012-08-01 00:00:00
abstract：:Optimal visualization of moving structures such as the heart and coronary arteries using digital radiographic imaging systems is a difficult problem that can involve tradeoffs between temporal, spatial, and density resolution. The motion dependence of four angiographic measures of vessel dimensions is given and demons...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.595651
更新日期：1985-11-01 00:00:00
abstract：PURPOSE:In the past decade, phase-contrast imaging (PCI) has been applied to study different kinds of tissues and human body parts, with an increased improvement of the image quality with respect to simple absorption radiography. A technique closely related to PCI is phase-retrieval imaging (PRI). Indeed, PCI is an ima...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.3447727
更新日期：2010-07-01 00:00:00
abstract：:The MCNP Monte Carlo radiation transport code was modified for diagnostic medical physics applications. In particular, the modified code was thoroughly benchmarked for the production of polychromatic tungsten x-ray spectra in the 30-150 kV range. Validating the modified code for coupled electron-photon transport with ...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.1288397
更新日期：2000-12-01 00:00:00
abstract：:A filtered backprojection algorithm is developed for single photon emission computed tomography (SPECT) imaging with an astigmatic collimator having a displaced center of rotation. The astigmatic collimator has two perpendicular focal lines, one that is parallel to the axis of rotation of the gamma camera and one that...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.598325
更新日期：1998-08-01 00:00:00
abstract：PURPOSE:In current clinical practice, there is no integrated 3D ultrasound (3DUS) guidance system clinically available for breast brachytherapy. In this study, the authors present a novel robot-assisted 3DUS system for real-time planning and guidance of breast interstitial high dose rate (HDR) brachytherapy treatment. ...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.4934832
更新日期：2015-12-01 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:Respiration-induced intrafraction target motion is a concern in liver cancer radiotherapy, especially in stereotactic body radiotherapy (SBRT), and therefore, verification of its motion is necessary. An effective means to localize the liver cancer is to insert metal fiducial markers to or near the tumor with si...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.3544369
更新日期：2011-02-01 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：:In a recent paper of Miller et al. (Med. Phys. 43(5), 2141-2152 (2016), the voltage dependence polarity effect of microionization chambers was studied. It was identified that polarity effect arises from the difference in electric potential between the collecting electrode and the guard electrode, which in turn deforms...
journal_title：Medical physics
pub_type： 信件
doi：10.1002/mp.12019
更新日期：2017-03-01 00:00:00
abstract：:Recently, new imaging modalities based on the detection of weak phase perturbations effects, among which are phase contrast and diffraction imaging, have been developed by several researchers. Due to their high sensitivity to weakly absorbing details, these techniques seem to be very promising for applications in the ...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.1388219
更新日期：2001-08-01 00:00:00
abstract：:Human tumors are characterized by an abnormal vascular network that develops because of unregulated angiogenesis. This contributes to abnormalities of the tumor microenvironment like hypoxia, acidosis and high interstitial fluid pressure that influence treatment response and patient survival. There is an important cli...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.4736156
更新日期：2012-06-01 00:00:00
abstract：:We are developing an automated stereo spot mammography technique for improved imaging of suspicious dense regions within digital mammograms. The technique entails the acquisition of a full-field digital mammogram, automated detection of a suspicious dense region within that mammogram by a computer aided detection (CAD...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.1737492
更新日期：2004-06-01 00:00:00
abstract：:The purpose of this paper is to develop a method that reduces the number of segments for intensity modulated arc therapy (IMAT) and intensity modulated radiotherapy (IMRT) for concave target volumes (TV). The aim was to utilize no more than two intensity levels per organ at risk (OAR) and to derive both optimal segmen...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.1861161
更新日期：2005-03-01 00:00:00
abstract：PURPOSE:To investigate energy deposition in glandular tissues of the breast on macro- and microscopic length scales in the context of mammography. METHODS:Multiscale mammography models of breasts are developed, which include segmented, voxelized macroscopic tissue structure as well as nine regions of interest (ROIs) e...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1002/mp.13372
更新日期：2019-03-01 00:00:00
abstract：PURPOSE:In the nuclear medicine department, the activity of radiopharmaceuticals is measured using dose calibrators (DCs) prior to patient injection. The DC consists of an ionization chamber that measures current generated by ionizing radiation (emitted from the radiotracer). In order to obtain an activity reading, the...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.4966027
更新日期：2016-12-01 00:00:00
abstract：PURPOSE:To increase diagnostic accuracy of breast MRI by increasing temporal resolution and more accurately sampling the early kinetics of contrast media uptake. We tested the feasibility of accelerating bilateral breast DCE-MRI by reducing the FOV, allowing aliasing, and unfolding the resulting images. METHODS:Previo...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1002/mp.12747
更新日期：2018-03-01 00:00:00
abstract：:Our purpose in this work is to demonstrate that the efficiency of dose-rate computations in 125I brachytherapy, using multigroup discrete ordinates radiation transport simulations, can be significantly enhanced using broad energy group cross sections without a loss of accuracy. To this end, the DANTSYS multigroup disc...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.1429238
更新日期：2002-02-01 00:00:00
abstract：PURPOSE:Metal artifact reduction (MAR) is a major problem and a challenging issue in x-ray computed tomography (CT) examinations. Iterative reconstruction from sinograms unaffected by metals shows promising potential in detail recovery. This reconstruction has been the subject of much research in recent years. However,...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.4950722
更新日期：2016-06-01 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：PURPOSE:The aim of this study was to develop a dose calculation method which is applicable to the interseed attenuation and the geometry lacking the equilibrium radiation scatter conditions in brachytherapy. METHODS:The dose obtained from measurement with a radiophotoluminescent glass rod dosimeter (GRD) was compared ...
journal_title：Medical physics
pub_type： 杂志文章
doi：10.1118/1.3590370
更新日期：2011-06-01 00:00:00
