Abstract:
PURPOSE:The absolute dose rate of the Imaging and Medical Beamline (IMBL) on the Australian Synchrotron was measured with a graphite calorimeter. The calorimetry results were compared to measurements from the existing free-air chamber, to provide a robust determination of the absolute dose in the synchrotron beam and provide confidence in the first implementation of a graphite calorimeter on a synchrotron medical beam line. METHODS:The graphite calorimeter has a core which rises in temperature when irradiated by the beam. A collimated x-ray beam from the synchrotron with well-defined edges was used to partially irradiate the core. Two filtration sets were used, one corresponding to an average beam energy of about 80 keV, with dose rate about 50 Gy/s, and the second filtration set corresponding to average beam energy of 90 keV, with dose rate about 20 Gy/s. The temperature rise from this beam was measured by a calibrated thermistor embedded in the core which was then converted to absorbed dose to graphite by multiplying the rise in temperature by the specific heat capacity for graphite and the ratio of cross-sectional areas of the core and beam. Conversion of the measured absorbed dose to graphite to absorbed dose to water was achieved using Monte Carlo calculations with the EGSnrc code. The air kerma measurements from the free-air chamber were converted to absorbed dose to water using the AAPM TG-61 protocol. RESULTS:Absolute measurements of the IMBL dose rate were made using the graphite calorimeter and compared to measurements with the free-air chamber. The measurements were at three different depths in graphite and two different filtrations. The calorimetry measurements at depths in graphite show agreement within 1% with free-air chamber measurements, when converted to absorbed dose to water. The calorimetry at the surface and free-air chamber results show agreement of order 3% when converted to absorbed dose to water. The combined standard uncertainty is 3.9%. CONCLUSIONS:The good agreement of the graphite calorimeter and free-air chamber results indicates that both devices are performing as expected. Further investigations at higher dose rates than 50 Gy/s are planned. At higher dose rates, recombination effects for the free-air chamber are much higher and expected to lead to much larger uncertainties. Since the graphite calorimeter does not have problems associated with dose rate, it is an appropriate primary standard detector for the synchrotron IMBL x rays and is the more accurate dosimeter for the higher dose rates expected in radiotherapy applications.
journal_name
Med Physjournal_title
Medical physicsauthors
Harty PD,Lye JE,Ramanathan G,Butler DJ,Hall CJ,Stevenson AW,Johnston PNdoi
10.1118/1.4870387subject
Has Abstractpub_date
2014-05-01 00:00:00pages
052101issue
5eissn
0094-2405issn
2473-4209journal_volume
41pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract::The dosimetric characteristics of a new dedicated radiosurgical treatment unit are systematically measured in terms of its percent depth dose, beam profile, and relative scatter factor. High-resolution diode detector, mini-ion-chamber detector, and conventional Kodak XV films are used to measure dosimetric data for a ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1494830
更新日期:2002-08-01 00:00:00
abstract::Computer-aided diagnostic (CAD) schemes have been developed to assist radiologists in the early detection of lung cancer in radiographs and computed tomography (CT) images. In order to improve sensitivity for nodule detection, many researchers have employed a filter as a preprocessing step for enhancement of nodules. ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1581411
更新日期:2003-08-01 00:00:00
abstract::The bremsstrahlung spectrum from an 8-MeV linear accelerator has been measured using a NaI(T1) spectrometer system. The spectrum shows a low-energy cutoff at 0.4 MeV and the maximum photon energy to be approximately 6% greater than the nominal energy. The maximum emission of energy fluence was 1.6 and 1.8 MeV for meas...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594221
更新日期:1976-05-01 00:00:00
abstract::The BrachySeed model LS-1 is one of the latest in a series of new brachytherapy 125I seeds that have recently become available commercially for interstitial implants. The dosimetric properties of the seed were investigated analytically, experimentally, and by Monte Carlo simulation. Following the AAPM Task Group 43 fo...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1445411
更新日期:2002-02-01 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:Because the small-radius photon beams shaped by cones in stereotactic radiosurgery (SRS) lack lateral electronic equilibrium and a detector's finite cross section, direct experimental measurement of dosimetric data for these beams can be subject to large uncertainties. As the dose calculation accuracy of a trea...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3488900
更新日期:2010-10-01 00:00:00
abstract:PURPOSE:This study aims to investigate carotid plaque calcification (CPC) using two-dimensional (2D) and 3D ultrashort echo time (UTE) magnetic resonance imaging (MRI) sequences and compare T1, T2*, water concentration, and bone mineral density (BMD) of CPC with those of cortical bone. METHODS:Twelve carotid plaque sp...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4819944
更新日期:2013-10-01 00:00:00
abstract:PURPOSE:Scattered radiation remains to be a major cause of image quality degradation in Flat Panel Detector (FPD)-based Cone-beam computed tomography (CBCT). We have been investigating a novel two-dimensional antiscatter grid (2D-ASG) concept to reduce scatter intensity, and hence improve CBCT image quality. We present...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12724
更新日期:2018-02-01 00:00:00
abstract::The dosimetry for radiocolloid therapy of cystic craniopharyngiomas is investigated. Analytical calculations based on the Loevinger and the Berger formulas for electrons and photons, respectively, are compared with Monte Carlo simulations. The role of the material of which the colloid introduced inside the craniophary...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1599653
更新日期:2003-09-01 00:00:00
abstract::Breast density is a strong predictor of the failure of mammography screening to detect breast cancer and is a strong predictor of the risk of developing breast cancer. The many imaging options that are now available for imaging dense breasts show great promise, but there is still the question of determining which wome...
journal_title:Medical physics
pub_type: 杂志文章,评审
doi:10.1118/1.4935141
更新日期:2015-12-01 00:00:00
abstract::Optical-resolution photoacoustic microscopy (OR-PAM) has been validated as a valuable tool for label-free volumetric microvascular imaging. More importantly, the advantages of noninvasiveness and measurement consistency suggest the use of OR-PAM for chronic imaging of intact microcirculation. Here, such chronic imagin...
journal_title:Medical physics
pub_type: 信件
doi:10.1118/1.3137572
更新日期:2009-06-01 00:00:00
abstract::A modified neutron production target assembly has been developed to provide improved performance of the proton-cyclotron-based neutron radiotherapy facility at the University of Washington for applications involving neutron capture enhanced fast-neutron therapy. The new target produces a neutron beam that yields essen...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598839
更新日期:2000-02-01 00:00:00
abstract::Surgical guidance with fluorescence has been demonstrated in individual clinical trials for decades, but the scientific and commercial conditions exist today for a dramatic increase in clinical value. In the past decade, increased use of indocyanine green based visualization of vascular flow, biliary function, and tis...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4951732
更新日期:2016-06-01 00:00:00
abstract:PURPOSE:This article presents a computer-aided diagnosis technique for improving the accuracy of the early diagnosis of Alzheimer's disease (AD). Two hundred and ten 18F-FDG PET images from the ADNI initiative [52 normal controls (NC), 114 mild cognitive impairment (MCI), and 53 AD subjects] are studied. METHODS:The p...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3488894
更新日期:2010-11-01 00:00:00
abstract:PURPOSE:A radiophotoluminescent glass rod dosimeter (RGD) has recently become commercially available. It is being increasingly used for dosimetry in radiotherapy to measure the absorbed dose including scattered low-energy photons on the body surface of a patient and for postal dosimetry audit. In this article, the dosi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4747261
更新日期:2012-10-01 00:00:00
abstract:PURPOSE:To establish accurate experimental dosimetry techniques for reference dose measurements in nonstandard composite fields. METHODS:A cylindrical PMMA phantom filled with water was constructed, at the center of which reference absorbed dose to water for a head and neck IMRT delivery was measured. Based on the pro...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3392247
更新日期:2010-06-01 00:00:00
abstract::The validity of conclusions drawn from multi-institutional radiotherapy studies is dependent upon the degree to which participating hospitals adhere to study requirements. A major effort undertaken by the Quality Assurance Review Center (QARC) assesses whether or not patient data which are deemed evaluable actually co...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595221
更新日期:1982-03-01 00:00:00
abstract::The modulation transfer function (MTF) and the noise power spectrum (NPS) are widely recognized as the most relevant metrics of resolution and noise performance in radiographic imaging. These quantities have commonly been measured using various techniques, the specifics of which can have a bearing on the accuracy of t...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2188816
更新日期:2006-05-01 00:00:00
abstract::Skeletal dosimetry based on microCT images of trabecular bone has recently been introduced to calculate the red bone marrow (RBM) and the bone surface cell (BSC) equivalent doses in human phantoms for external exposure to photons. In order to use the microCT images for skeletal dosimetry, spongiosa voxels in the skele...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3242266
更新日期:2009-11-01 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::This investigation contains the results of exposure measurements on two types of clinical I-125 seeds: a model 6702 no-marker seed, and a model 6711 silver wire seed. Measurements were made locally with a parallel-plate mammography chamber, traceable to the National Bureau of Standards (NBS) calibration. The same seed...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595784
更新日期:1985-03-01 00:00:00
abstract::The scattered-photon part of pencil-beam dose kernels for high-energy x-ray beams can be derived experimentally by differentiating the broad-beam scatter-to-primary dose ratio as a function of radius. Formally, this requires a uniform and parallel beam, and the procedure is complicated by the nonideal, actual beam con...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597884
更新日期:1996-09-01 00:00:00
abstract::A method to correct for geometric image distortion in the x-ray imaging chain, so-called dewarping, has been developed. A global two-dimensional polynomial model of which the degree is optimized is used. The performance of the method has been tested in a number of experiments using images of a plate with a 1 cm spaced...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598101
更新日期:1997-12-01 00:00:00
abstract::Linac calibration is done in water, but patients are comprised primarily of soft tissue. Conceptually, and specified in NRG/RTOG trials, dose should be reported as dose-to-muscle to describe the dose to the patient. Historically, the dose-to-water of the linac calibration was often converted to dose-to-muscle for pati...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13995
更新日期:2020-03-01 00:00:00
abstract::The physical characteristics of a clinical charge coupled device (CCD)-based imager (Senovision, GE Medical Systems, Milwaukee, WI) for small-field digital mammography have been investigated. The imager employs a MinR 2000 (Eastman Kodak Company, Rochester, NY) scintillator coupled by a 1:1 optical fiber to a front-il...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1286720
更新日期:2000-08-01 00:00:00
abstract::Determination of the relaxation times T1 and T2 which are important for tissue characterization generally requires the use of different pulse sequences in magnetic resonance imaging. In this study, a new pulse sequence which facilitates simultaneous determination of the T1 and T2 times is presented. Determination take...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595867
更新日期:1986-09-01 00:00:00
abstract::Two or more angiograms are being used frequently in medical imaging to reconstruct locations in three-dimensional (3D) space, e.g., for reconstruction of 3D vascular trees, implanted electrodes, or patient positioning. A number of techniques have been proposed for this task. In this simulation study, we investigate th...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2008467
更新日期:2005-09-01 00:00:00
abstract::The determination of the radiation exposure history of the population has become increasingly important in the study of the effects of low-level radiation. The present work was started to try to obtain an in vivo dosimeter that could give an indication of radiation exposure. Dental enamel is the only living tissue whi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595768
更新日期:1985-05-01 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:PURPOSE:Credentialing can have an impact on whether or not a clinical trial produces useful quality data that is comparable between various institutions and scanners. With the recent increase of dynamic contrast enhanced-computed tomography (DCE-CT) usage as a companion biomarker in clinical trials, effective quality a...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4812429
更新日期:2013-08-01 00:00:00