Abstract:
:Recent working groups of the AAPM [Almond et al., Med. Phys. 26, 1847 (1999)] and the IAEA (Andreo et al., Draft V.7 of "An International Code of Practice for Dosimetry based on Standards of Absorbed Dose to Water," IAEA, 2000) have described guidelines to base reference dosimetry of high energy photon beams on absorbed dose to water standards. In these protocols use is made of the absorbed-dose beam quality conversion factor, kQ which scales an absorbed-dose calibration factor at the reference quality 60Co to a quality Q, and which is calculated based on state-of-the-art ion chamber theory and data. In this paper we present the measurement and analysis of beam quality conversion factors kQ for cylindrical chambers in high-energy photon beams. At least three chambers of six different types were calibrated against the Canadian primary standard for absorbed dose based on a sealed water calorimeter at 60Co [TPR10(20)=0.572, %dd(10)x=58.4], 10 MV [TPR10(20)=0.682, %dd(10)x=69.6), 20 MV (TPR10(20)=0.758, %dd(10)x= 80.5] and 30 MV [TPR10(20) = 0.794, %dd(10)x= 88.4]. The uncertainty on the calorimetric determination of kQ for a single chamber is typically 0.36% and the overall 1sigma uncertainty on a set of chambers of the same type is typically 0.45%. The maximum deviation between a measured kQ and the TG-51 protocol value is 0.8%. The overall rms deviation between measurement and the TG-51 values, based on 20 chambers at the three energies, is 0.41%. When the effect of a 1 mm PMMA waterproofing sleeve is taken into account in the calculations, the maximum deviation is 1.1% and the overall rms deviation between measurement and calculation 0.48%. When the beam is specified using TPR10(20), and measurements are compared with kQ values calculated using the version of TG-21 with corrected formalism and data, differences are up to 1.6% when no sleeve corrections are taken into account. For the NE2571 and the NE2611A chamber types, for which the most literature data are available, using %dd(10)x, all published data show a spread of 0.4% and 0.6%, respectively, over the entire measurement range, compared to spreads of up to 1.1% for both chambers when the kQ values are expressed as a function of TPR10(20). For the PR06-C chamber no clear preference of beam quality specifier could be identified. When comparing the differences of our kQ measurements and calculations with an analysis in terms of air-kerma protocols with the same underlying calculations but expressed in terms of a compound conversion factor CQ, we observe that a system making use of absorbed-dose calibrations and calculated kQ values, is more accurate than a system based on air-kerma calibrations in combination with calculated CQ (rms deviation of 0.48% versus 0.67%, respectively).
journal_name
Med Physjournal_title
Medical physicsauthors
Seuntjens JP,Ross CK,Shortt KR,Rogers DWdoi
10.1118/1.1328081subject
Has Abstractpub_date
2000-12-01 00:00:00pages
2763-79issue
12eissn
0094-2405issn
2473-4209journal_volume
27pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract:PURPOSE:There is significant current interest in the use of biological image guidance in radiotherapy planning. In lung-cancer treatment, tumor motion due to respiration is known to be a limitation. This is particularly true in PET, where image data are collected over a number of minutes. An in-house-developed 4D PET a...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3276776
更新日期:2010-02-01 00:00:00
abstract::The data from Meisberger et al. [Radiology 90, 953-957 (1968)] are often used as a basis for dose calculations in brachytherapy. In order to describe the absorbed dose in water around a brachytherapy point source, Meisberger provided a polynomial fit for different isotopes taking into account the effect of attenuation...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597583
更新日期:1995-05-01 00:00:00
abstract:PURPOSE:The authors use reduced-order constrained optimization (ROCO) to create clinically acceptable IMRT plans quickly and automatically for advanced lung cancer patients. Their new ROCO implementation works with the treatment planning system and full dose calculation used at Memorial Sloan-Kettering Cancer Center (M...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3575416
更新日期:2011-05-01 00:00:00
abstract::Compared with slice-by-slice approaches for SPECT reconstruction, three-dimensional iterative methods provide a more accurate physical model and an improved SPECT image. Clinical application of these methods, however, is limited primarily to their computational demands. This paper investigates the methods for approxim...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598030
更新日期:1997-09-01 00:00:00
abstract::The concept of equivalent uniform dose (EUD) has been suggested as a means to quantitatively consider heterogeneous dose distributions within targets. Tumor cell density/function is typically assumed to be uniform. We herein propose to use 18F-labeled 2-deoxyglucose (FDG) positron emission tomography (PET) tumor imagi...
journal_title:Medical physics
pub_type: 临床试验,杂志文章
doi:10.1118/1.1779372
更新日期:2004-09-01 00:00:00
abstract::Studies suggest that clinical outcomes are improved in repeat trigeminal neuralgia (TN) Gamma Knife radiosurgery if a different part of the nerve from the previous radiosurgery is treated. The MR images taken in the first and repeat radiosurgery need to be coregistered to map the first radiosurgery volume onto the sec...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1944287
更新日期:2005-07-01 00:00:00
abstract:PURPOSE:The efficiency of radioembolization procedures could be greatly enhanced if results of the 99m Tc-MAA pretreatment procedure were immediately available in the interventional suite, enabling 1-day procedures as a result of direct estimation of the hepatic radiation dose and lung shunt fraction. This would, howev...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13253
更新日期:2019-01-01 00:00:00
abstract::Variation of the photoactivation rate across radiation fields of three different bremsstrahlung beams of two medical accelerators has been measured, making use of the photonuclear reactions in natural indium probes: 115In(y,y')115mIn and 115In(y,n)114mIn. The third nuclear reaction, 115In(n,y)116mIn, was used to detec...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598558
更新日期:1999-04-01 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::A method is described for calibration of 192Ir high-dose-rate (HDR) brachytherapy afterloading systems. Since NIST does not offer calibration of ionization chambers with the gamma-ray spectrum of iridium-192, an interpolation procedure is employed, using calibrations above (137Cs, 662 keV) and below (250 kVcp, 146-keV...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596649
更新日期:1991-05-01 00:00:00
abstract::A clamp-on current probe utilizing the Hall effect was used to determine x-ray tube current. This noninvasive technique was compared to two other methods of mA measurement: the Machlett Dynalyzer and the mR/mAs linearity method. Three diagnostic x-ray units were used in the comparison; two modern three-phase rooms and...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596080
更新日期:1987-03-01 00:00:00
abstract:PURPOSE:Diabetic retinopathy (DR) is one of the most widespread causes of preventable blindness in the world. The most dangerous stage of this condition is proliferative DR (PDR), in which the risk of vision loss is high and treatments are less effective. Fractal features of the retinal vasculature have been previously...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12627
更新日期:2017-12-01 00:00:00
abstract::Results of a human observer performance study using a new ultrasound contrast-detail (CD) phantom are reported. The new phantom allows estimates of the fundamental statistical uncertainties involved in CD analysis. Results of these experiments show that observers generally considered to be "trained" require experience...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597147
更新日期:1993-01-01 00:00:00
abstract:PURPOSE:The authors introduce a novel method for defining standardized uptake values (SUVs) in PET∕CT based on routinely collected CT data. The goal of the study is to reduce, if possible, the variability of SUV in a heterogeneous population. Two well established methods for defining SUV are based on body weight (BW) a...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4816656
更新日期:2013-09-01 00:00:00
abstract::Total scalp irradiation is a treatment technique used for a variety of superficial malignancies. Helical tomotherapy is an effective technique used for total scalp irradiation. Recent published work has shown the TomoTherapy planning system to overestimate the superficial dose. In this study, the superficial doses for...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2996288
更新日期:2008-11-01 00:00:00
abstract::Vessel size measurement is perhaps the most often performed quantitative analysis in diagnostic and interventional angiography. Although automated vessel sizing techniques are generally considered to have good accuracy and precision, we have observed that clinicians rarely use these techniques in standard clinical pra...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1562491
更新日期:2003-04-01 00:00:00
abstract:PURPOSE:Plastic scintillation detectors are used for dosimetry in small radiation fields with high dose gradients, e.g., provided by β-emitting sources like 106 Ru/106 Rh eye plaques. A drawback is a background signal caused by Cerenkov radiation generated by electrons passing the optical fibers (light guides) of this ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12374
更新日期:2017-09-01 00:00:00
abstract::Four different expressions, derived from the diffusion theory or the random walk model, were used to fit time-resolved reflectance data for the evaluation of tissue optical properties. The experimental reflectance curves were obtained from phantoms of known optical parameters (absorption and transport scattering coeff...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597739
更新日期:1996-09-01 00:00:00
abstract:PURPOSE:In C-arm computed tomography (CT), the field of view (FOV) is often not sufficient to acquire certain anatomical structures, e.g., a full hip or thorax. Proposed methods to extend the FOV use a fixed detector displacement and a 360° scan range to double the radius of the FOV. These trajectories are designed for...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4915542
更新日期:2015-05-01 00:00:00
abstract:PURPOSE:The ionizing radiation imparted to patients during computed tomography exams is raising concerns. This paper studies the performance of a scheme called dose reduction using prior image constrained compressed sensing (DR-PICCS). The purpose of this study is to characterize the effects of a statistical model of x...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4773866
更新日期:2013-02-01 00:00:00
abstract::Noise characterization through estimation of the noise power spectrum (NPS) is a central component of the evaluation of digital x-ray systems. We begin with a brief review of the fundamentals of NPS theory and measurement, derive explicit expressions for calculation of the one- and two-dimensional (1D and 2D) NPS, and...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598623
更新日期:1999-07-01 00:00:00
abstract::Molecular imaging is the direct or indirect noninvasive monitoring and recording of the spatial and temporal distribution of in vivo molecular, genetic, and/or cellular processes for biochemical, biological, diagnostic, or therapeutic applications. Molecular images that indicate the presence of malignancy can be acqui...
journal_title:Medical physics
pub_type: 杂志文章,评审
doi:10.1118/1.4819818
更新日期:2013-10-01 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:PURPOSE:The most appropriate method of evaluating the effective atomic number necessitates consideration of energy-dependent behavior. Previously, this required quite laborious calculation, which is why many scientists revert to over-simplistic power-law methods. The purpose of this work is to develop user-friendly sof...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3689810
更新日期:2012-04-01 00:00:00
abstract:PURPOSE:High-quality radiation therapy using highly conformal dose distributions and image-guided techniques requires optimum machine delivery performance. In this work, a monitoring system for multileaf collimator (MLC) performance, integrating semiautomated MLC quality control (QC) tests and statistical process contr...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4901520
更新日期:2014-12-01 00:00:00
abstract::Backscatter factors for kVps and half-value layers typical of mammographic beams have been determined as a function of beam diameter and half-value layer. The method utilized thin TLD-100 chips with the scattering medium alternately present and absent. Results indicate that the field-size dependence of the backscatter...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594312
更新日期:1977-09-01 00:00:00
abstract::Direct comparisons of the National Institute of Standards and Technology's (NIST) Ritz 20 kV to 100 kV standard free-air ionization chamber and a portable variable-length free-air ionization chamber designed by the University of Wisconsin-Madison Accredited Dosimetry Calibration Laboratory (UW-ADCL) were made on NISTs...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598148
更新日期:1997-08-01 00:00:00
abstract::Two experimental methods are described for obtaining average energies of neutron spectra produced by an electron accelerator in a medical treatment room. In the first method, the dose equivalent is measured by means of indium activation foils in an Andersson-Braun moderator. Fluences are determined by the usual activa...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595662
更新日期:1985-11-01 00:00:00
abstract::An automated data-acquisition and analysis system has been developed for dosimetry measurements on the pion therapy beam at the Clinton P. Anderson Meson Physics Facility Biomedical Channel in Los Alamos using a PDP-11/45 computer and CAMAC interface. Initialization, test, and monitor programs allow the user to set th...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594418
更新日期:1978-03-01 00:00:00
abstract:PURPOSE:Silicon photodetectors are of significant interest for use in positron emission tomography (PET) systems due to their compact size, insensitivity to magnetic fields, and high quantum efficiency. However, one of their main disadvantages is fluctuations in temperature cause strong shifts in gain of the devices. P...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4903889
更新日期:2015-01-01 00:00:00