Abstract:
:A method of computing optimized intensity-modulated beam profiles has been further developed and used to generate highly conformal radiotherapy dose distributions. The features of these distributions are shown to be strongly dependent on the tuning built into the algorithm. The optimization aims to achieve a specified dose prescription with a posteriori computation of probabilistic biological response. A method has been developed to show the effect of stratifying the intensity-modulated beam profiles into a number of finite intensity increments. It is shown that, provided the number of intensity strata is not too small, highly conformal dose distributions can be achieved with a number of fields (e.g. 7 or 9) which is not excessively large. This number, however, depends on the exact shape of the planning target volume (PTV and its disposition with respect to juxtaposed organs at risk (OARs). These intensity-modulated profiles can therefore be delivered either by apparatus for 'tomotherapy' or by using the multileaf collimator at each gantry orientation to deliver a sequence of fixed fields with different field sizes, constructing the beam profile via finite increments of beam intensity. When the PTV and OARS overlap, due to including a finite margin on the clinical target volume to account for tissue movement, it is shown that the dose delivered to the overlap region provides a limit on what can be achieved with conformal therapy. This problem is encountered, for example, when treating the prostate which lies next to part of the rectum and bladder. Some comment is provided on, but not a solution for, the problem of optimizing field orientation.
journal_name
Phys Med Bioljournal_title
Physics in medicine and biologyauthors
Webb Sdoi
10.1088/0031-9155/39/12/007subject
Has Abstractpub_date
1994-12-01 00:00:00pages
2229-46issue
12eissn
0031-9155issn
1361-6560journal_volume
39pub_type
杂志文章abstract::The purpose of this paper for four-dimensional (4D) computed tomography (CT) is threefold. (1) A new spatiotemporal model is presented from the matrix perspective with the row dimension in space and the column dimension in time, namely the robust PCA (principal component analysis)-based 4D CT model. That is, instead o...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/56/11/002
更新日期:2011-06-07 00:00:00
abstract::Permanent in vivo verification of IMRT photon beam profiles by a radiation detector with spatial resolution, positioned on the radiation entrance side of the patient, has not been clinically available so far. In this work we present the DAVID system, which is able to perform this quality assurance measurement while th...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/51/5/013
更新日期:2006-03-07 00:00:00
abstract::Mean glandular dose is the quantity used for dosimetry in mammography and depends on breast-related characteristics, such as thickness and density, and on the x-ray spectrum used for breast imaging. This work aims to present an experimentally-based method to derive polyenergetic normalized glandular dose coefficients ...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/ab171a
更新日期:2019-05-10 00:00:00
abstract::The aim of this study is to calculate realistic dose distributions that include the continuous deformation of organs and continuous motion of machine using 4D Monte Carlo methods for both volumetric modulated arc therapy and helical tomotherapy treatments. As part of a previous study, we presented a method to perform ...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/58/9/2807
更新日期:2013-05-07 00:00:00
abstract::In recent codes of practice for reference dosimetry in clinical proton beams using ionization chambers, it is recommended to perform the measurement in a water phantom. However, in situations where the positioning accuracy is very critical, it could be more convenient to perform the measurement in a plastic phantom. I...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/47/17/302
更新日期:2002-09-07 00:00:00
abstract::The results of optimization of inverse treatment plans depend on a choice of the objective function. Even when the optimal solution for a given cost function can be obtained, a better solution may exist for a given clinical scenario and it could be obtained with a revised objective function. In the approach presented ...
journal_title:Physics in medicine and biology
pub_type: 临床试验,杂志文章
doi:10.1088/0031-9155/49/12/003
更新日期:2004-06-21 00:00:00
abstract::Automatic cell cycle analysis (DNA histograms) is usually performed with flow cytometry. In cases when only few cells are available, the DNA content has to be measured with a fluorescence microscope combined with sensitive camera systems (SIT, MCP, cooled CCDs) and a frame grabber for image analysis. The fluorescent c...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/41/3/013
更新日期:1996-03-01 00:00:00
abstract::Beam hardening is inevitable due to the polychromatic X-ray spectrum and energy-dependent attenuation coefficients of materials, leading to the underestimation of artifacts arising from projection data, especially on metal regions. State-of-the-art research on beam-hardening artifacts is based on a numerical method th...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/abe026
更新日期:2021-01-26 00:00:00
abstract::Fixed-pattern noise in electronic portal images (EPIs) is normally eliminated by dividing raw image data by an open-field calibration image (OFCI). However, for successful elimination, there must be exact registration between the two image sets. Any movement within the imaging system, such as that which occurs with ga...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/41/11/007
更新日期:1996-11-01 00:00:00
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journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/aa9502
更新日期:2017-12-19 00:00:00
abstract::Results from dielectric studies on the freshwater fish Cyprinus carpio exposed to a sublethal concentration of sodium alkyl benzene sulphonate were compared with those from untreated control fish; recovery from the test solution was also checked. The influence of the anionic detergent on the intracellular matter of fi...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/29/5/005
更新日期:1984-05-01 00:00:00
abstract::Radiation dose calculation using models of the human anatomy has been a subject of great interest to radiation protection, medical imaging, and radiotherapy. However, early pioneers of this field did not foresee the exponential growth of research activity as observed today. This review article walks the reader through...
journal_title:Physics in medicine and biology
pub_type: 杂志文章,评审
doi:10.1088/0031-9155/59/18/R233
更新日期:2014-09-21 00:00:00
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journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/59/6/1339
更新日期:2014-03-21 00:00:00
abstract::Evaluation of the radioisotopic purity of technetium-99m (99mTc) produced in GBq amounts by proton bombardment of enriched molibdenum-100 (100Mo) metallic targets at low proton energies (i.e. within 15-20 MeV) is conducted. This energy range was chosen since it is easily achievable by many conventional medical cyclotr...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/aadc88
更新日期:2018-09-19 00:00:00
abstract::A pencil beam model for the calculation of the lateral scattering in water of protons for any therapeutic energy and depth is presented. It is based on the full Molière theory, taking into account the energy loss and the effects of mixtures and compounds. Concerning the electromagnetic part, the model has no free para...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/61/4/N102
更新日期:2016-02-21 00:00:00
abstract::Four dimensional cone beam computed tomography (4DCBCT) uses a constant gantry speed and imaging frequency that are independent of the patient's breathing rate. Using a technique called respiratory motion guided 4DCBCT (RMG-4DCBCT), we have previously demonstrated that by varying the gantry speed and imaging frequency...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/62/11/4300
更新日期:2017-06-07 00:00:00
abstract::In this work, we propose a framework for optimizing spectral CT imaging parameters and hardware design with regard to material classification tasks. Compared with conventional CT, many more parameters must be considered when designing spectral CT systems and protocols. These choices will impact material classification...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/61/12/4599
更新日期:2016-06-21 00:00:00
abstract::Uncertainties in determining clinically used relative biological effectiveness (RBE) values for ion beam therapy carry the risk of absolute and relative misestimations of RBE-weighted doses for clinical scenarios. This study assesses the consequences of hypothetical misestimations of input parameters to the RBE modell...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/57/23/7983
更新日期:2012-12-07 00:00:00
abstract::Compact gamma cameras with a square-shaped monolithic scintillator crystal and an array of silicon photomultipliers (SiPMs) are actively being developed for applications in areas such as small animal imaging, cancer diagnostics and radiotracer guided surgery. Statistical methods of position reconstruction, which are p...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/aa6029
更新日期:2017-05-07 00:00:00
abstract::The advent of real-time ultrasound in the 1970s, together with a growing interest in tissue characterization, led to a number of investigators using the nature of tissue motion to distinguish healthy from diseased tissue. Our group at the (then) Ultrasonics Institute demonstrated the use of phase methods for detecting...
journal_title:Physics in medicine and biology
pub_type: 历史文章,杂志文章
doi:10.1088/0031-9155/45/6/301
更新日期:2000-06-01 00:00:00
abstract::A theoretical analysis is presented of the biologically effective dose of the solar long wave ultraviolet radiation (UVA) received by patients who are being treated for psoriasis by oral psoralen photochemotherapy. It is shown that patients treated during the summer months in the UK may well receive a UV dose which is...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/26/6/011
更新日期:1981-11-01 00:00:00
abstract::The widely applied single-interaction analytic expression characterizing the energy resolution component of the angular resolution precision for an electronically collimated point source is extended to include multiple-interaction Compton scatter sequences as well as sequences terminated by photoelectric absorption. T...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/43/10/021
更新日期:1998-10-01 00:00:00
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journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/aaaa95
更新日期:2018-02-21 00:00:00
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journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/41/10/024
更新日期:1996-10-01 00:00:00
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journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/43/1/001
更新日期:1998-01-01 00:00:00
abstract::The signal properties of polycrystalline mercuric iodide (HgI2) film detectors, under irradiation conditions relevant to mammographic, radiographic, fluoroscopic and radiotherapy x-ray imaging, are reported. Each film detector consists of an approximately 230 to approximately 460 microm thick layer of HgI2 (fabricated...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/50/12/012
更新日期:2005-06-21 00:00:00
abstract::A step and shoot sequencer was developed that can be integrated into an IMRT optimization algorithm. The method uses non-uniform fluence steps and is adopted to the constraints of an MLC. It consists of a clustering, a smoothing and a segmentation routine. The performance of the algorithm is demonstrated for eight mat...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/46/7/319
更新日期:2001-07-01 00:00:00
abstract::The degradation of low energy electrons in a methane based, tissue equivalent gas was studied experimentally by ionization chamber experiments and theoretically by Monte Carlo electron transport simulation in the energy range between 25 eV and 5 keV. From measured ionization yields and calculated ionization and energy...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/37/5/008
更新日期:1992-05-01 00:00:00
abstract::In this study, we explore the potential of compressed sensing (CS) accelerated broadband 3D phase-encoded turbo spin-echo (3D-PE-TSE) for the purpose of geometrically undistorted imaging in the presence of field inhomogeneities. To achieve this goal 3D-PE-SE and 3D-PE-TSE sequences with broadband rf pulses and dedicat...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/0031-9155/60/2/615
更新日期:2015-01-21 00:00:00
abstract::The first trimester fetal ultrasound scan is important to confirm fetal viability, to estimate the gestational age of the fetus, and to detect fetal anomalies early in pregnancy. First trimester ultrasound images have a different appearance than for the second trimester scan, reflecting the different stage of fetal de...
journal_title:Physics in medicine and biology
pub_type: 杂志文章
doi:10.1088/1361-6560/ab3ad1
更新日期:2019-09-17 00:00:00