Abstract:
:One of the key components in modern LINAC room shielding design is the amount of 90 degrees head leakage radiation levels. With the general clinical acceptance of intensity-modulated radiation therapy (IMRT) technique, accurate knowledge of this quantity has become even more important. Measurement of 90 degrees head leakage radiation of medical linear accelerators can be technically challenging due to the low dose rate causing poor signal-to-noise ratios in most detectors. 90 degrees leakage tenth-value layer (TVL) values in concrete have not been reported for the Elekta linear accelerators. This report describes our measurements of 90 degrees leakage TVL values for 6, 10, and 18 MV x-ray beams for an Elekta Precise Treatment System. A large-volume (1000 cm3) unpressurized ionization chamber and a high sensitivity electrometer, together with a separate chamber bias power supply, were used in these measurements in order to maximize the signal-to-noise ratio. A lead enclosure, of minimum thickness 10 cm, was constructed inside the treatment room to house the ion chamber to reduce the influence of room-scattered radiation. A square aperture of 10 X 10 cm2 area was left in the shield and aimed towards the accelerator head. Measurements were performed with the chamber placed at approximately 2 m from the accelerator isocenter. Concrete slabs with individual dimensions of approximately 40 X 40 cm2 cross-sectional area and 5 cm thickness were placed between the accelerator head and the ion chamber for these measurements. The measurements were performed with total concrete thickness of up to 80 cm, so that values up to the third TVL were measured. These measurements showed thatthe first concrete TVL values are 22, 23, and 28 cm (8.6, 9.1, and 10.5 in.) for 6, 10, and 18 MV beams, while the average of the first 3 TVL's were 25, 26, and 29 cm (9.9, 10.2, and 11.5 in.). Measured values agreed to within 10% of previously reported values for Varian linear accelerators for equivalent radiation beam qualities.
journal_name
Med Physjournal_title
Medical physicsauthors
Li Z,Mutic S,Low Ddoi
10.1118/1.2335489subject
Has Abstractpub_date
2006-09-01 00:00:00pages
3541-5issue
9eissn
0094-2405issn
2473-4209journal_volume
33pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract::Cone beam transmission CT (CB-CT) improves SPECT imaging by providing high-quality attenuation maps for attenuation compensation and for correlated SPECT and CT imaging. The present work measures the detection nonuniformity for CB-CT implemented with a gamma camera, and applies nonuniformity corrections to make CB-CT ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596838
更新日期:1992-03-01 00:00:00
abstract:PURPOSE:To develop a novel aperture-based algorithm for volumetric modulated are therapy (VMAT) treatment plan optimization with high quality and high efficiency. METHODS:The VMAT optimization problem is formulated as a large-scale convex programming problem solved by a column generation approach. The authors consider...
journal_title:Medical physics
pub_type: 信件
doi:10.1118/1.3491675
更新日期:2010-11-01 00:00:00
abstract::While simple, intravascular brachytherapy (IVB) presents a considerable potential for harm to the patient. The medical physicist maintains the responsibility to minimize the likelihood of operational problems or dosimetric errors. The principals for safe operation remain the same as with any radiotherapy treatment: to...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1524167
更新日期:2002-12-01 00:00:00
abstract:PURPOSE:Bilateral filters have been substantially exploited in numerous magnetic resonance (MR) image restoration applications for decades. Due to the deficiency of theoretical basis on the filter parameter setting, empirical manipulation with fixed values and noise variance-related adjustments has generally been emplo...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12157
更新日期:2017-04-01 00:00:00
abstract::As different types of radionuclides (e.g., 131Cs source) are introduced for clinical use in brachytherapy, the question is raised regarding whether a relatively simple method exists for the derivation of values of the half value layer (HVL) or the tenth value layer (TVL). For the radionuclide that has been clinically ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2905356
更新日期:2008-06-01 00:00:00
abstract:PURPOSE:To quantify detector perturbation effects in megavoltage small photon fields and support the theoretical explanation on the nature of quality correction factors in these conditions. METHODS:In this second paper, a modern approach to radiation dosimetry is defined for any detector and applied to small photon fi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4930798
更新日期:2015-10-01 00:00:00
abstract:PURPOSE:Although small animal image-guided radiotherapy (SA-IGRT) systems are used increasingly in preclinical research, tools for performing routine quality assurance (QA) have not been optimized and are not readily available. Robust, efficient, and reliable QA tools are needed to ensure the accuracy and reproducibili...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12939
更新日期:2018-07-01 00:00:00
abstract::Significant advances have been made in recent years to improve photon dose calculation. However, accurate prediction of dose perturbation effects near the interfaces of different media, where charged particle equilibrium is not established, remain unsolved. Furthermore, changes in atomic number, which affect the multi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597611
更新日期:1995-07-01 00:00:00
abstract:PURPOSE:To investigate whether functionally-weighted dose-volume histogram (DVH) parameters are more predictive of radiation-induced pneumonitis (RP) than standard parameters such as V20 and mean lung dose (MLD). MATERIALS AND METHODS:A retrospective chart review identified 26 patients who received curative-intent rad...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4740190
更新日期:2012-07-01 00:00:00
abstract:PURPOSE:Accurate detection of pulmonary nodules remains a technical challenge in computer-aided diagnosis systems because some nodules may adhere to the blood vessels or the lung wall, which have low contrast compared to the surrounding tissues. In this paper, the analysis of typical shape features of candidate nodules...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4907961
更新日期:2015-03-01 00:00:00
abstract::In the present investigation, the necessary tests for implementing a quality assurance program for a commercial treatment planning system (TPS), recently installed at Sao Paulo University School of Medicine Clinicas Hospital-Brazil, was established and performed in accordance with the new IAEA publication TRS 430, and...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2742779
更新日期:2007-07-01 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::The large variation of x-ray fluence at the detector in cone-beam CT (CBCT) poses a significant challenge to detectors' limited dynamic range, resulting in the loss of skinline as well as reduction of CT number accuracy, contrast-to-noise ratio, and image uniformity. The authors investigate the performance of a bowtie...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3017470
更新日期:2009-01-01 00:00:00
abstract:PURPOSE:Radiation therapy is often delivered by multiple sequential treatment plans. For an accurate radiobiological evaluation of the overall treatment, fractionation corrections to each dose distribution must be applied before summing the three-dimensional dose matrix of each plan since the simpler approach of perfor...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4792636
更新日期:2013-03-01 00:00:00
abstract:PURPOSE:To compare esophageal dose distributions in esophageal sparing IMRT plans with predicted dose distributions which include the effect of inter-fraction motion. METHODS:Seven lung cancer patients were used, each with a standard and an esophageal sparing plan (74Gy, 2Gy fractions). The average max dose to esophag...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4735647
更新日期:2012-06-01 00:00:00
abstract::This article is the first in a series on the calculation of electron dose using multiple-scattering theory. In it we develop a unified theory, which we term Gaussian multiple-scattering theory, starting from a number of contributions already in the literature: the Fermi-Eyges multiple-scattering theory, the Yang path ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596166
更新日期:1988-03-01 00:00:00
abstract:PURPOSE:High resolution three-dimensional (3D) magnetic resonance (MR) images are well suited for automated cartilage segmentation in the human knee joint. However, volumetric scans such as 3D Double-Echo Steady-State (DESS) images are not routinely acquired in clinical practice which limits opportunities for reliable ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14421
更新日期:2020-10-01 00:00:00
abstract::Nuclear magnetic resonance (NMR) imaging of perfluorocarbon (PFC) emulsions and neat liquids has shown potential for in vivo oxygen imaging in blood and organ tissue. PFC compounds exhibit complicated NMR spectra caused by chemical shifts and spin-spin couplings which can lead to artifacts and degraded spatial resolut...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595960
更新日期:1986-07-01 00:00:00
abstract:PURPOSE:To examine the response properties of cylindrical cavity ionization chambers (ICs) in the depth-ionization buildup region so as to obtain a robust chamber-signal - based method for definitive water surface identification, hence absolute ionization chamber depth localization. METHOD & MATERIALS:An analytical mo...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12319
更新日期:2017-07-01 00:00:00
abstract::Scanning film densitometry routinely used for obtaining dosimetric information about therapy treatment beams is subject to several sources of inaccuracies. The most significant of these are described and appropriate methods of testing are presented. This establishes the need for adequate acceptance testing followed by...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595407
更新日期:1983-09-01 00:00:00
abstract::In the last 30 years, thousands of basic or clinical studies have been devoted to atherosclerosis or to the problem of restenosis after angioplasty. In these studies, axial stresses in the vessel wall have received practically no attention, contrary to circumferential stress and purely biological aspects. Based on a r...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1844432
更新日期:2005-02-01 00:00:00
abstract::An important aspect of heavy charged particle radiotherapy is its ability to localize dose to the target volume. Current techniques generally employ beam delivery schemes which use range modulated beams in which the Bragg peak is spread out over a range of depths. The range modulation is constant over the entire beam ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595419
更新日期:1983-11-01 00:00:00
abstract:PURPOSE:Adding magnetic resonance (MR)-derived information to standard transrectal ultrasound (TRUS) images for guiding prostate biopsy is of substantial clinical interest. A tumor visible on MR images can be projected on ultrasound (US) by using MR-US registration. A common approach is to use surface-based registratio...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4917481
更新日期:2015-05-01 00:00:00
abstract:PURPOSE:Calculations of deoxyribonucleic acid (DNA) damages involve many parameters in the computation process. As these parameters are often subject to uncertainties, it is of central importance to comprehensively quantify their impacts on DNA single-strand break (SSB) and double-strand break (DSB) yields. This has be...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14036
更新日期:2020-04-01 00:00:00
abstract::We have studied the effect of real-time optical image processing (OIP) in an image intensifier/television (II-TV) radiographic imaging system by using a liquid-crystal display (LCD) placed between the II and the TV camera. The LCD compresses the dynamic range of the transmitted image by modulating the spatial distribu...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596199
更新日期:1988-11-01 00:00:00
abstract::Empirical functions that describe primary beam profiles for radiotherapy treatment planning systems generally account for finite source size only on beams unmodified by blocks, wedges, or compensating filters. To incorporate the effects of extended sources on such modified beams and to treat the effect of an extended ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596222
更新日期:1988-09-01 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:Lung cancer is a major cause of cancer deaths, and the 5-year survival rate of stage IV lung cancer patients is only 2%. However, the 5-year survival rate of stage I lung cancer patients significantly increases to 50%. As such, spiral computed tomography (CT) scans are necessary to diagnose high-risk lung cance...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12331
更新日期:2017-08-01 00:00:00
abstract:PURPOSE:The aim of this work is to search for new metrics that could give more reliable acceptance/rejection criteria on the IMRT verification process and to offer solutions to the discrepancies found among different conventional metrics. Therefore, besides conventional metrics, new ones are proposed and evaluated with...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4964796
更新日期:2016-11-01 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