Abstract:
PURPOSE:Megavoltage grid therapy is currently delivered with step-and-shoot multisegment techniques or using a high attenuation block with divergent holes. However, the commercial availability of grid blocks is limited, their construction is difficult, and step-and-shoot techniques require longer treatment times and are not practical with some multileaf collimators. This work studies the feasibility of a hybrid collimation system for grid therapy that does not require multiple segments and can be easily implemented with widely available technical means. METHODS:The authors have developed a system to generate a grid of beamlets by the simultaneous use of two perpendicular sets of equally spaced leaves that project stripe patterns in orthogonal directions. One of them is generated with the multileaf collimator integrated in the accelerator and the other with an in-house made collimator constructed with a low melting point alloy commonly available at radiation oncology departments. The characteristics of the grid fields for 6 and 18 MV have been studied with a shielded diode, an unshielded diode, and radiochromic film. RESULTS:The grid obtained with the hybrid collimation is similar to some of the grids used clinically with respect to the beamlet size (about 1 cm) and the percentage of open beam (1/4 of the total field). The grid fields are less penetrating than the open fields of the same energy. Depending on the depth and the direction of the profiles (diagonal or along the principal axes), the measured valley-to-peak dose ratios range from 5% to 16% for 6 MV and from 9% to 20% for 18 MV. All the detectors yield similar results in the measurement of profiles and percent depth dose, but the shielded diode seems to overestimate the output factors. CONCLUSIONS:The combination of two stripe pattern collimators in orthogonal directions is a feasible method to obtain two-dimensional arrays of beamlets and has potential usefulness as an efficient way to deliver grid therapy. The implementation of this method is technically simpler than the construction of a conventional grid block.
journal_name
Med Physjournal_title
Medical physicsauthors
Almendral P,Mancha PJ,Roberto Ddoi
10.1118/1.4801902subject
Has Abstractpub_date
2013-05-01 00:00:00pages
051712issue
5eissn
0094-2405issn
2473-4209journal_volume
40pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract:PURPOSE:Real-time adaptive planning and treatment has been infeasible due in part to its high computational complexity. There have been many recent efforts to utilize graphics processing units (GPUs) to accelerate the computational performance and dose accuracy in radiation therapy. Data structure and memory access pat...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4895822
更新日期:2014-10-01 00:00:00
abstract::Routine electron beam quality assurance requires an accurate, yet practical, method of energy characterization. Subtle shifts in beam energy may be produced by the linac bending magnet assembly, and the sensitivity of a commercially available electron beam energy-monitoring device for monitoring these small energy dri...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.599033
更新日期:2000-07-01 00:00:00
abstract:PURPOSE:The depth dose of a monoenergetic broad parallel proton beam has been modeled in a number of ways, but evidently not yet for oblique incidence. The purpose of this investigation is to find an accurate analytic formula for this case, which can then be used to model the depth dose of a broad beam with an initial ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3495969
更新日期:2010-11-01 00:00:00
abstract:PURPOSE:A three-dimensional finite element analysis based canine heart model is introduced that would enable the assessment of cardiac function. METHODS:The three-dimensional canine heart model is based on the cardiac deformation and motion model obtained from the Cardiac Mechanics Research Group at UCSD. The canine h...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3496326
更新日期:2010-11-01 00:00:00
abstract:PURPOSE:To develop a new scintillating fiber-based electronic portal imaging device (EPID) with a high quantum efficiency (QE) while preserving an adequate spatial resolution. METHODS:Two prototypes were built: one with a single pixel readout and the other with an active matrix flat-panel imager (AMFPI) for readout. T...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13900
更新日期:2020-01-01 00:00:00
abstract:PURPOSE:Bone strength is the key factor impacting fracture risk. Assessment of bone strength from high-resolution (HR) images have largely relied on linear micro-finite element analysis (μFEA) even though failure always occurs beyond the yield point, which is outside the linear regime. Nonlinear μFEA may therefore be m...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4802085
更新日期:2013-05-01 00:00:00
abstract:PURPOSE:Integrating a linac with a magnetic resonance imager (MRI) will revolutionize the accuracy of external beam radiation treatments. Irradiating in the presence of a strong magnetic field, however, will modify the dose distribution. These dose modifications have been investigated previously, mainly using Monte Car...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12413
更新日期:2017-09-01 00:00:00
abstract::To develop volumetric micro-CT fluoroscopy for small animal imaging, we have proposed a cone-beam system with multiple x-ray sources. In this paper, we extend Parker's single-source half-scan weighting scheme to the case of an odd number of x-ray sources that are equiangularly distributed, and apply it for half-scan F...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1381549
更新日期:2001-07-01 00:00:00
abstract:PURPOSE:Currently, in clinical practice of intensity-modulated proton therapy (IMPT), the influence of the minimum monitor unit (MU) constraint is taken into account through postprocessing after the optimization is completed. This may degrade the plan quality and plan robustness. This study aims to mitigate the impact ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12677
更新日期:2018-01-01 00:00:00
abstract::A method to significantly reduce the exposure area product in fluoroscopy using a pre-patient region-of-interest (ROI) attenuator is presented. The attenuator has a thin central region and a gradually increasing thickness away from the center. It is shown that the unwanted brightening artifact caused by the attenuator...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1470205
更新日期:2002-05-01 00:00:00
abstract:PURPOSE:X-ray phase-contrast tomography (PCT) is a rapidly emerging imaging modality for reconstructing estimates of an object's three-dimensional x-ray refractive index distribution. Unlike conventional x-ray computed tomography methods, the statistical properties of the reconstructed images in PCT remain unexplored. ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3267548
更新日期:2010-01-01 00:00:00
abstract:PURPOSE:This article aims to introduce a novel algorithm for fast beam angle selection in intensity modulated radiotherapy (IMRT). METHODS:The algorithm models the optimization problem as a beam angle ranking problem and chooses suitable beam angles according to their rank. A new parameter called "beam intensity profi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3517866
更新日期:2010-12-01 00:00:00
abstract:PURPOSE:Dual-energy computed tomography and dual-energy cone-beam computed tomography (DE-CBCT) are promising modalities for applications ranging from vascular to breast, renal, hepatic, and musculoskeletal imaging. Accordingly, the optimization of imaging techniques for such applications would benefit significantly fr...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4736420
更新日期:2012-08-01 00:00:00
abstract::We are developing computerized methods for characterizing the bone texture pattern from digitized skeletal radiographs. For this method to be useful clinically, it must be able to distinguish between weak and strong bone under the range of exposure conditions potentially encountered in the clinical setting. In this st...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598858
更新日期:2000-01-01 00:00:00
abstract::A Monte Carlo computer study of the total dose distribution from neutrons and prompt gamma emissions (but excluding the contribution from conversion and Auger electrons) for gadolinium neutron capture therapy of brain tumors has been carried out in order to test the theoretic feasibility of this modality using commerc...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596761
更新日期:1992-09-01 00:00:00
abstract::Intensity modulated radiation therapy (IMRT) treatment planning typically considers beam optimization and beam delivery as separate tasks. Following optimization, a multi-leaf collimator (MLC) or other beam delivery device is used to generate fluence patterns for patient treatment delivery. Due to limitations and char...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1477230
更新日期:2002-06-01 00:00:00
abstract::The goal is to perform geometric studies on cone-beam CT scanning along a three-dimensional (3D) spiral of variable radius. First, the background for variable radius spiral cone-beam scanning is given in the context of electron-beam CT/micro-CT. Then, necessary and sufficient conditions are proved for existence and un...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1751251
更新日期:2004-06-01 00:00:00
abstract:PURPOSE:Several works have recently focused on flattening-filter-free (FFF) beams of linear accelerators of various companies (in particular, Varian and Elekta), but no overview as yet exists for the flattening-filter free 7XU beam (Siemens Artiste). METHODS:Dosimetric properties of the 7XU beam were measured in May a...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3703835
更新日期:2012-05-01 00:00:00
abstract:PURPOSE:Respiratory gating in PET is an approach used to minimize the negative effects of respiratory motion on spatial resolution. It is based on an initial determination of a patient's respiratory movements during a scan, typically using hardware based systems. In recent years, several fully automated databased algor...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3483784
更新日期:2010-10-01 00:00:00
abstract:PURPOSE:Since the first publications on intensity modulated radiation therapy (IMRT) in the early 1980s almost all efforts have been focused on fairly time consuming dynamic or segmental multileaf collimation. With narrow fast scanned photon beams, the flexibility and accuracy in beam shaping increases, not least in co...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3615059
更新日期:2011-08-01 00:00:00
abstract::We describe the use of a graphical mathematical spreadsheet programming environment which can be used to simulate the acquisition and reconstruction processes of an x-ray computed tomography (CT) machine. The simulation is used to study the effect of photon counting statistics on the noise in the reconstructed image. ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598654
更新日期:1999-08-01 00:00:00
abstract:PURPOSE:To investigate the use of local noise power spectrum (NPS) to characterize image noise and wavelet analysis to isolate defective pixels and inter-subpanel flat-fielding artifacts for quantitative quality assurance (QA) of electronic portal imaging devices (EPIDs). METHODS:A total of 93 image sets including cus...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4959541
更新日期:2016-09-01 00:00:00
abstract::A method for the in vivo determination of the isocenter dose, Diso, and mid-plane dose, Dm, using the transmitted signal St measured by 25 central pixels of an aSi-based EPID is here reported. The method has been applied to check the conformal radiotherapy of pelvic tumors and supplies accurate in vivo dosimetry avoid...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2360014
更新日期:2006-11-01 00:00:00
abstract::Effects of changes in the physics of EGSnrc compared to EGS4/PRESTA on energy deposition kernels for monoenergetic photons and on dose point kernels for beta sources in water are investigated. In the diagnostic energy range, Compton binding corrections were found to increase the primary energy fraction up to 4.5% at 3...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1861412
更新日期:2005-03-01 00:00:00
abstract::This paper describes a multileaf collimator, designed to obtain irregularly shaped neutron fields, that fits into an existing fixed field-size collimator system. The shape of the desired portal field is obtained by appropriately setting the position of each leaf of the collimator. The collimator consists of 40 polyeth...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596084
更新日期:1987-03-01 00:00:00
abstract::Monte Carlo (MC) simulations were performed to estimate brachytherapy dose distributions for Collaborative Ocular Melanoma Study (COMS) eye plaques. Brachytherapy seed models 200, 6711, and CS-1 Rev2 carrying 103Pd, 125I, and 131Cs radionuclides, respectively, were modeled and benchmarked against previously published ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2940604
更新日期:2008-07-01 00:00:00
abstract:PURPOSE:To develop a novel three-dimensional (3D) hybrid-encoding framework using compressed sensing (CS) and Toeplitz encoding with variable phase-scrambled radio-frequency (RF) excitation, which has the following advantages: low power deposition of RF pulses, reduction of the signal dynamic range, no additional hardw...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13987
更新日期:2020-04-01 00:00:00
abstract:PURPOSE:Computational models are widely used during the design and characterization of microwave ablation (MWA) devices, and have been proposed for pretreatment planning. Our objective was to assess three-dimensional (3D) transient temperature and ablation profiles predicted by MWA computational models with temperature...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14318
更新日期:2020-09-01 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:PURPOSE:To design and quantify the shielding efficacy of an inner Borated Polyethylene (BPE)wall for a 15 MV linac in a low energy vault. METHODS:A Varian TrueBeam linac with a maximum photon energy of 15 MV was installed in asmaller, preexisting vault. This vault originally housed a low-energy machine and did not hav...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4735334
更新日期:2012-06-01 00:00:00