Abstract:
:Electron spectral reconstruction of medical accelerators from measured depth doses is a practical method for providing the input initial phase space distribution at the patient surface that is required by Monte Carlo treatment planning systems. The posed inverse problem of spectral reconstruction is ill conditioned and this may lead to nonphysical oscillations in the reconstructed spectra. Use of a variational method of solution with a regularization technique removes the oscillations but tends to smooth the sharp (deltalike) energy peak that is a common feature in electron spectra generated by medical accelerators. Because the sharp peak contains a large percentage of the electrons in the spectrum, an accurate estimate of the peak width, height and position is critical to the success of the technique for spectrum reconstruction with regularization. We propose use of an adaptive regularization term as a special form of the general Tichonov regularization function. The variational method with the adaptive regularization term is applied to reconstruct electron spectra for the 6, 9, and 18 MeV electron beams of a Varian Clinac 2100C accelerator and proves to be a very simple, effective and accurate approach. Results using this variational method with adaptive regularization almost perfectly reconstruct electron spectra from depth dose distributions.
journal_name
Med Physjournal_title
Medical physicsauthors
Wei J,Sandison GA,Chvetsov AVdoi
10.1118/1.2161404subject
Has Abstractpub_date
2006-02-01 00:00:00pages
354-9issue
2eissn
0094-2405issn
2473-4209journal_volume
33pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract::Both the design considerations and the dosimetric properties of the Siemens Model 5800 linear accelerator are discussed. This unit is of such an energy (3.3 MV) as to imitate Cobalt-60 teletherapy depth doses. A linear relation of dmax to depth dose at low energies was found for various wave guides and targets. The en...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596487
更新日期:1990-05-01 00:00:00
abstract:PURPOSE:The aim of this study was to assess the suitability of Gafchromic EBT3 films for reference dose measurements in the beam of a prototype high dose-per-pulse linear accelerator (linac), capable of delivering electron beams with a mean dose-rate (Ḋm ) ranging from 0.07 to 3000 Gy/s and a dose-rate in pulse (Ḋp ) o...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12066
更新日期:2017-02-01 00:00:00
abstract::The purpose of this work is to show the feasibility of using in vivo proton radiography of a radiotherapy patient for the patient individual optimization of the calibration from CT-Hounsfield units to relative proton stopping power. Water equivalent tissue (WET) calibrated proton radiographs of a dog patient treated f...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1833041
更新日期:2005-01-01 00:00:00
abstract:PURPOSE:State of the art to access radiofrequency (RF) heating near implants is computer modeling of the devices and solving Maxwell's equations for the specific setup. For a set of input parameters, a fixed result is obtained. This work presents a theoretical approach in the alternating current (ac) limit, which can p...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3637495
更新日期:2011-10-01 00:00:00
abstract:PURPOSE:To analyze the noise performance of the edge illumination phase-based x-ray imaging technique when applying "single-shot" phase retrieval. The latter consists in applying a sample-specific low-pass filter to the raw data, leading to "hybrid" images in which phase and attenuation contrast are merged with each ot...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14366
更新日期:2020-09-01 00:00:00
abstract::We measured the characteristic curve, modulation transfer function (MTF), and the Wiener spectrum of a commercially available computed radiographic (CR) system with photostimulable phosphor plate (imaging plate, IP). The characteristic curve (system response) obtained by an inverse-square x-ray sensitometry showed a w...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596402
更新日期:1989-01-01 00:00:00
abstract::The aim of this study is to perform a statistical analysis to verify the calculated percentage depth dose (PDD) based on the tissue maximum ratio (TMR) with the PDD measurements taken in water. 6 and 15 MV photon beams produced by a Varian linear 2100 C/D accelerator were used. PDDs and TMRs were measured at various d...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4740131
更新日期:2012-07-01 00:00:00
abstract:PURPOSE:To automatically detect and isolate areas of low and high stiffness temporal stability in shear wave elastography (SWE) image sequences and define their impact in chronic liver disease (CLD) diagnosis improvement by means of clinical examination study and deep learning algorithm employing convolutional neural n...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13521
更新日期:2019-05-01 00:00:00
abstract:PURPOSE:To assess the temporal and spatial accuracy of the GateCT™ system (VisionRT, London, UK), a recently released respiratory tracking system for 4DCT, under both ideal and nonideal respiratory conditions. METHODS:Three experiments were performed by benchmarking and comparing its results with the ground-truth inpu...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3671941
更新日期:2012-01-01 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::Permanent implantation of 125I (iodine) or 103Pd (palladium) sources is a popular treatment option in the management of early stage prostate cancer. New sources are being developed, some of which are being marketed for different clinical applications. A new technique of adjuvant stereotactic permanent seed breast impl...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3006151
更新日期:2008-12-01 00:00:00
abstract::A spread-out Bragg peak (SOBP) is used in proton beam therapy to create a longitudinal conformality of the required dose to the target. In order to create this effect in a passive beam scattering system, a variety of components must operate in conjunction to produce the desired beam parameters. We will describe how th...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2776255
更新日期:2007-10-01 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::Heating rate (HR) patterns in cylindrical structures were studied with inhomogeneous limb phantoms. These phantoms, arm and thigh models consisting of fat, bone, and muscle material, were heated with Clini-Therm L, M, and MS applicators at 915 MHz. The thigh model is 18 cm in diameter with 2.65-cm-thick fat on the out...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596627
更新日期:1991-11-01 00:00:00
abstract:PURPOSE:In intensity-modulated proton therapy (IMPT), protons are used to deliver highly conformal dose distributions, targeting tumors, and sparing organs-at-risk. However, due to uncertainties in both patient setup and relative stopping power (RSP) calculation, margins are added to the treatment volume during treatme...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14347
更新日期:2020-09-01 00:00:00
abstract::A simple noninvasive method is described for determining the backscatter to a monitor chamber of a medical accelerator based on the measurement of charge deposited in the target. This method is compared quantitatively to the more elaborate telescopic method for photon beams of 6 MV and 15 MV on linear accelerators hav...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598203
更新日期:1998-03-01 00:00:00
abstract:PURPOSE:The study aims to investigate whether Nakagami parameters--estimated from the statistical distribution of the backscattered ultrasound radio-frequency (RF) signals--could provide a means for quantitative characterization of parotid-gland injury resulting from head-and-neck radiotherapy. METHODS:A preliminary c...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4862507
更新日期:2014-02-01 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:Modern CT systems adjust X-ray flux accommodating for patient size to achieve certain image noise values. The effectiveness of this adaptation is an important aspect of CT performance and should ideally be characterized in the context of real patient cases. The objective of this study was to characterize CT per...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12172
更新日期:2017-06-01 00:00:00
abstract::Monte Carlo calculations have been performed for the purpose of characterizing the dosimetric properties of three brachytherapy sources. The three sources are manufactured by Syncor Pharmaceuticals Inc. and consist of two 125I seeds (BT-125-1 and BT-125-2) and one 103Pd seed (BT-103-3). The BT-125-1 and BT-125-2 seed ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1469627
更新日期:2002-05-01 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:To show that Cherenkov emission is generated by external radiotherapy beam in tissue, and could serve as optical source to excite an oxygen sensitive phosphor, Oxyphor G4, within tissue. The intensity and lifetime of the phosphorescence was measured with a time-gated system and reveals the oxygenation levels in...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4734811
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:To study the impact of target geometrical and linac operational parameters, such as target material and thickness, electron beam size, repetition rate, and mean current on the ability of the radiotherapy treatment head to deliver high-dose-rate x-ray irradiation in the context of novel linear accelerators capab...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12615
更新日期:2017-12-01 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::A comprehensive performance testing program is an essential ingredient of high-quality single-photon emission computed tomography (SPECT). Many of the procedures previously published are complicated, time consuming, or require a special testing environment. This Task Group developed a protocol for evaluating SPECT ima...
journal_title:Medical physics
pub_type: 指南,杂志文章
doi:10.1118/1.597605
更新日期:1995-04-01 00:00:00
abstract::Statistical image reconstruction (SIR) methods have shown potential to substantially improve the image quality of low-dose x-ray computed tomography (CT) as compared to the conventional filtered back-projection (FBP) method. According to the maximum a posteriori (MAP) estimation, the SIR methods are typically formulat...
journal_title:Medical physics
pub_type: 杂志文章,评审
doi:10.1002/mp.13123
更新日期:2018-10-01 00:00:00
abstract::The objective of this work is to assess the suitability and performance of a new dosimeter system with a novel geometry for the quality assurance (QA) of volumetric modulated arc therapy (VMAT). The new dosimeter system consists of a hollow cylinder (15 and 25 cm inner and outer diameters) with 124 diodes embedded in ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3117563
更新日期:2009-05-01 00:00:00
abstract::The assessment of differential left and right lung function is important for patients under consideration for lung resection procedures such as single lung transplantation. We developed an automated, knowledge-based segmentation algorithm for purposes of deriving functional information from dynamic computed tomography...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598898
更新日期:2000-03-01 00:00:00
abstract:PURPOSE:The spatial resolution of iterative reconstruction (IR) in computed tomography (CT) is contrast- and noise-dependent because of the nonlinear regularization. Due to the severe noise contamination, it is challenging to perform precise spatial-resolution measurements at very low-contrast levels. The purpose of th...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4916802
更新日期:2015-05-01 00:00:00
abstract::A study of the objective imaging characteristics of a new asymmetric screen-film system is presented herein. The system is characterized by high x-ray absorption asymmetric screens, and a low-noise, high-contrast asymmetric film having near-zero crossover. Comparisons are made with the imaging characteristics of two w...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597407
更新日期:1994-09-01 00:00:00