Abstract:
:A technique was developed to reduce the size and magnitude of the hot and cold spots in the abutting regions of photon and electron fields. The photon and electron fields were set up such that the photon field extended approximately 2 cm into the electron field in the abutting region. The region of the photon beam that overlapped the electron field was modulated using a multileaf collimator, effectively broadening the photon penumbra to make it complimentary to the electron penumbra. The computer calculations were verified using film measurements for abutting a 6 MV photon beam with a 9 MeV electron beam. A uniform dose was achieved at a prespecified depth of 2 cm, and dose uniformity was improved at the specified depth and beyond compared with unmodulated photon beams. A slight increase in dose inhomogeneity was seen at shallower depths. The overall areas of the hot and cold spots were significantly reduced. The technique also reduced the sensitivity of dose homogeneity to setup errors such that the magnitudes of the hot and cold spots were about half of those produced with unmodulated photon beam when an overlap or gap of 4 mm was introduced. The technique was applied to the treatment of a head and neck cancer and a lymphoma involving the right pleura with markedly reduced dose inhomogeneity in the abutting regions.
journal_name
Med Physjournal_title
Medical physicsauthors
Li JG,Xing L,Boyer AL,Hamilton RJ,Spelbring DR,Turian JVdoi
10.1118/1.598753subject
Has Abstractpub_date
1999-11-01 00:00:00pages
2379-84issue
11eissn
0094-2405issn
2473-4209journal_volume
26pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract:PURPOSE:To estimate organ and effective radiation doses due to backscatter security scanners using Monte Carlo simulations and a voxelized phantom set. METHODS:Voxelized phantoms of male and female adults and children were used with the GEANT4 toolkit to simulate a backscatter security scan. The backscatter system was...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4718680
更新日期:2012-06-01 00:00:00
abstract::Assessment of clinic and site specific margins are essential for the effective use of three-dimensional and intensity modulated radiation therapy. An electronic portal imaging device (EPID) based methodology is introduced which allows individual and population based CTV-to-PTV margins to be determined and compared wit...
journal_title:Medical physics
pub_type: 临床试验,杂志文章
doi:10.1118/1.1800712
更新日期:2004-11-01 00:00:00
abstract:PURPOSE:Phase contrast imaging, particularly of the breast, is being actively investigated. The purpose of this work is to investigate the x-ray phase contrast properties of breast tissues and commonly used breast tissue substitutes or phantom materials with an aim of determining the phantom materials best representati...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4794503
更新日期:2013-04-01 00:00:00
abstract:PURPOSE:Intraoperative electron radiation therapy (IOERT) involves the delivery of a high radiation dose during tumor resection in a shorter time than other radiation techniques, thus improving local control of tumors. However, a linear accelerator device is needed to produce the beam safely. Mobile linear accelerators...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12482
更新日期:2017-10-01 00:00:00
abstract:PURPOSE:To develop and test the feasibility of a two-pass iterative reconstruction algorithm with material decomposition designed to obtain quantitative iodine measurements in digital breast tomosynthesis. METHODS:Contrast-enhanced mammography has shown promise as a cost-effective alternative to magnetic resonance ima...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14400
更新日期:2020-10-01 00:00:00
abstract:PURPOSE:Two diodes which do not require correction factors for small field relative output measurements are designed and validated using experimental methodology. This was achieved by adding an air layer above the active volume of the diode detectors, which canceled out the increase in response of the diodes in small f...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4894728
更新日期:2014-10-01 00:00:00
abstract::A multislit collimator was designed and fabricated for basic studies on microbeam radiation therapy (MRT) with an x-ray energy of about 100 keV. It consists of 30 slits that are 25 microm high, 30 mm wide, and 5 mm thick in the beam direction. The slits were made of 25 microm-thick polyimide sheets that were separated...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2940157
更新日期:2008-07-01 00:00:00
abstract::The effective energy of the x-ray beam from linear accelerators changes as a function of the position in the beam due to nonuniform filtration by the flattening filter. In this work, the transmittance through a water column was measured in good geometry and the beam quality characterized in units of HVL in water. Meas...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594677
更新日期:1980-03-01 00:00:00
abstract::A detailed Monte Carlo study of the PTW-diamond solid state detector response in megavoltage photon beams (60Co gamma rays to 25 MV x rays) has been performed with the EGS4 Monte Carlo Code. The sensitive volume of the diamond detector is a disk of diameter 4.4 mm and thickness 0.40 mm. The phantom material was water ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598771
更新日期:1999-11-01 00:00:00
abstract:PURPOSE:Recent guidance by The Joint Commission and CRCPD recommendations require establishing CT reference dose levels (RDLs) for clinical protocols and recording CT dose metrics in the patient's medical record. This presentation addresses which dose values in the CT report should be recorded for the purposes of monit...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4734773
更新日期:2012-06-01 00:00:00
abstract::Computed tomography dose index (CTDI) is a conventional indicator of the patient dose in CT studies. It is measured as the integration of the longitudinal single scan dose profile (SSDP) by using a 100-mm-long pencil ionization chamber and a single axial scan. However, the assumption that most of the SSDP is contained...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1835571
更新日期:2005-01-01 00:00:00
abstract:PURPOSE:The authors investigated the potential of optimized noncoplanar irradiation trajectories for volumetric modulated arc therapy (VMAT) treatments of nasopharyngeal patients and studied the trade-off between treatment plan quality and delivery time in radiation therapy. METHODS:For three nasopharyngeal patients, ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4914863
更新日期:2015-05-01 00:00:00
abstract::Frequent and repeated imaging procedures such as those performed in image-guided radiotherapy (IGRT) programs may add significant dose to radiosensitive organs of radiotherapy patients. It has been shown that kV-CBCT results in doses to bone that are up to a factor of 3-4 higher than those in surrounding soft tissue. ...
journal_title:Medical physics
pub_type: 信件
doi:10.1118/1.3014197
更新日期:2008-12-01 00:00:00
abstract::A single-field rotational total skin electron irradiation technique has recently been developed at the McGill University for treatment of skin malignancies. The dose received by a given surface point during rotation in a uniform large electron field depends on the radius of rotation of the surface point, on the local ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595524
更新日期:1984-07-01 00:00:00
abstract:PURPOSE:The hematopoietically active tissues of skeletal bone marrow are a prime target for computational dosimetry given potential risks of leukemia and, at higher dose levels, acute marrow toxicity. The complex three-dimensional geometry of trabecular spongiosa, however, complicates schema for dose assessment in such...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12002
更新日期:2017-01-01 00:00:00
abstract:PURPOSE:The purpose of this study was to develop a practical method for estimating organ doses from kilovoltage cone-beam CT (CBCT) that can be performed with readily available phantoms and dosimeters. The accuracy of organ dose estimates made using the ImPACT patient dose calculator was also evaluated. METHODS:A 100 ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3476459
更新日期:2010-09-01 00:00:00
abstract:PURPOSE:Cone beam computed tomography (CBCT) image quality suffers from contamination from scattered photons in the projection images. Monte Carlo simulations are a powerful tool to investigate the properties of scattered photons.egs_cbct, a recent EGSnrc user code, provides the ability of performing fast scatter calcu...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4881142
更新日期:2014-07-01 00:00:00
abstract:PURPOSE:To investigate the accuracy of output factor measurements using a commercial (Exradin W1, SI) and a prototype, "in-house" developed, plastic scintillation dosimeter (PSD) in small photon fields. METHODS:Repetitive detector-specific output factor OFdet measurements were performed in water (parallel to the CAX) ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12064
更新日期:2017-02-01 00:00:00
abstract:PURPOSE:The liver segments divided by Couinaud classification method are used to understand the functional anatomy of liver, which is significant in hepatic resection surgery. In Couinaud classification method, each third-order branch of the portal vein (PV) defines the supplied territory of a corresponding liver segme...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.14745
更新日期:2021-02-02 00:00:00
abstract::Extensive information has been made available relative to the physical aspects necessary for calculation of radiation absorbed dose from radiopharmaceuticals. A similar data base for the biological factors involved in these calculations has not been documented as thoroughly. The authors present an extensive literature...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594679
更新日期:1980-05-01 00:00:00
abstract:PURPOSE:The purpose of this study is to estimate the effect of edema, developed during implant procedure, on tumor cell surviving fraction(SF) and tumor control probability(TCP) in the patients of prostate cancer who underwent 131 Cs permanent seed implants. METHODS:The impact of edema on SF and TCP, was calculated us...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4735061
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:Effective dose (ED) is a widely used metric for comparing ionizing radiation burden between different imaging modalities, scanners, and scan protocols. In computed tomography (CT), ED can be estimated by performing scans on an anthropomorphic phantom in which metal-oxide-semiconductor field-effect transistor (M...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4868693
更新日期:2014-04-01 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::Current edge detection methods used to determine coronary artery dimensions from digital (DSA) images suffer a strong dependence on the system's modulation transfer function (MTF). The videodensitometric algorithms are less sensitive to MTF blurring, yet still result in an overestimation of the vessel size of 10% to 2...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596370
更新日期:1989-03-01 00:00:00
abstract:PURPOSE:Normal patient databases (NPDs) are used to distinguish between normal and abnormal perfusion in SPECT myocardial perfusion imaging (MPI) and have gained wide acceptance in the clinical environment, yet there are limitations to this approach. This study introduces a template-based method for semi-quantitative M...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3595112
更新日期:2011-07-01 00:00:00
abstract:PURPOSE:Cone-beam CT (CBCT) images contain severe shading artifacts mostly due to scatter. Many algorithms have been proposed to alleviate this problem by data correction on projections. Sophisticated methods have also been designed to further improve the image quality when prior patient information is available. In th...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4736218
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:Small animal immobilization devices facilitate positioning of animals for reproducible imaging and accurate focal radiation therapy. In this study, the authors demonstrate the use of three-dimensional (3D) printing technology to fabricate a custom-designed mouse head restraint. The authors evaluate the accuracy...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4933200
更新日期:2015-11-01 00:00:00
abstract:PURPOSE:Flattening filter free (FFF) beams generated by medical linear accelerators have recently started to be used in radiotherapy clinical practice. Such beams present fundamental differences with respect to the standard filter flattened (FF) beams, making the generally used dosimetric parameters and definitions not...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4754799
更新日期:2012-10-01 00:00:00
abstract:PURPOSE:To apply the dual ionization chamber method for mixed radiation fields to an accurate comparison of the secondary neutron dose arising from the use of a tungsten alloy multileaf collimator (MLC) as opposed to a brass collimator system for defining the shape of a therapeutic proton field. METHODS:Hydrogenous an...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3656025
更新日期:2011-11-01 00:00:00
abstract:PURPOSE:Current respiratory motion monitoring devices used for motion synchronization in medical imaging and radiotherapy provide either 1D respiratory signal over a specific region or 3D information based on few external or internal markers. On the other hand, newer technology may offer the potential to monitor the en...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3589131
更新日期:2011-06-01 00:00:00