Abstract:
PURPOSE:The complex beam delivery techniques for patient treatment using a clinical linear accelerator (linac) may result in variations in the photon spectra, which can lead to dosimetric differences in patients that cannot be accounted for by current treatment planning systems (TPSs). Therefore, precise knowledge of the fluence and energy spectrum (ES) of the therapeutic beam is very important. However, owing to the high energy and flux of the beam, the ES cannot be measured directly, and validation of the spectrum modeled in the TPS is difficult. The aim of this study is to develop an efficient beam transmission measurement procedure for accurately reconstructing the ES of a therapeutic x-ray beam generated by a clinical linac. METHODS:The attenuation of a 6 MV photon beam from an Elekta Synergy Platform clinical linac through different thicknesses of graphite and lead was measured using an ion chamber. The response of the ion chamber as a function of photon energy was obtained using the Monte Carlo (MC) method in the Geant4 simulation code. Using the curves obtained in the photon beam transmission measurements and the ion chamber energy response, the ES was reconstructed using an iterative algorithm based on a mathematical model of the spectrum. To evaluate the accuracy of the spectrum reconstruction method, the reconstructed ES (ESrecon ) was compared to that determined by the MC simulation (ESMC ). RESULTS:The ion chamber model in the Geant4 simulation was well validated by comparing the ion chamber perturbation factors determined by the TRS-398 calibration protocol and EGSnrc; the differences were within 0.57%. The number of transmission measurements was optimized to 10 for efficient spectrum reconstruction according to the rate of increase in the spectrum reconstruction accuracy. The distribution of ESrecon obtained using the measured transmission curves was clearly similar to the reference, ESMC , and the dose distributions in water calculated using ESrecon and ESMC were similar within a 2% local difference. However, in a heterogeneous medium, the dose discrepancy between them was >5% when a complex beam delivery technique composed of 171 control points was used. CONCLUSIONS:The proposed measurement procedure required a total time of approximately 1 h to obtain and analyze 20 transmission measurements. In addition, it was confirmed that the transmission curve of high-Z materials influences the accuracy of spectrum reconstruction more than that of low-Z materials. A well-designed transmission measurement protocol suitable for clinical environments could be an essential tool for better dosimetric accuracy in patient treatment and for periodic verification of the beam quality.
journal_name
Med Physjournal_title
Medical physicsauthors
Choi HJ,Park H,Yi CY,Kim BC,Shin WG,Min CHdoi
10.1002/mp.13569subject
Has Abstractpub_date
2019-07-01 00:00:00pages
3285-3297issue
7eissn
0094-2405issn
2473-4209journal_volume
46pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract:PURPOSE:The authors investigate the extent to which Response Evaluation Criteria in Solid Tumors (RECIST) can predict tumor volumes in ideal geometric settings and using clinical data. METHODS:The authors consider a hierarchy of models including uniaxial ellipsoids, general ellipsoids, and composites of ellipsoids, us...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3577602
更新日期:2011-05-01 00:00:00
abstract::The Radiological Physics Center (RPC) developed two heterogeneous anthropomorphic quality assurance phantoms for use in verifying the accuracy of radiation delivery: one for intensity-modulated radiation therapy (IMRT) to the pelvis and the other for stereotactic body radiation therapy (SBRT) to the thorax. The purpos...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2737158
更新日期:2007-06-01 00:00:00
abstract::Computed tomography colonography (CTC) is a minimally invasive method that allows the evaluation of the colon wall from CT sections of the abdomen/pelvis. The primary goal of CTC is to detect colonic polyps, precursors to colorectal cancer. Because imperfect cleansing and distension can cause portions of the colon wal...
journal_title:Medical physics
pub_type: 临床试验,杂志文章
doi:10.1118/1.1796171
更新日期:2004-10-01 00:00:00
abstract::The performance of a diode array (Profiler) was evaluated by comparing its enhanced dynamic wedge (EDW) profiles measured at various depths with point measurements using a 0.03 cm3 ionization chamber on a commercial linear accelerator. The Profiler, which covers a 22.5 cm width, was used to measure larger field widths...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598019
更新日期:1997-07-01 00:00:00
abstract::Monte Carlo dose calculations will potentially reduce systematic errors that may be present in currently used dose calculation algorithms. However, Monte Carlo calculations inherently contain random errors, or statistical uncertainty, the level of which decreases inversely with the square root of computation time. Our...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598916
更新日期:2000-03-01 00:00:00
abstract::Neutron energy spectra and spectra of dose deposition in tissue-equivalent material have been measured for neutron sources produced by 16-, 22-, 35-, and 45.5-MeV deuterons and 22.5-, 35-, 45-, and 65.5-MeV protons incident upon a thick beryllium target. Neutron spectra were measured using time-of-flight techniques an...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594392
更新日期:1977-05-01 00:00:00
abstract::A photon transport algorithm for fully three-dimensional radiotherapy treatment planning has been developed based on the discrete ordinates (SN) solution of the Boltzmann equation. The algorithm is characterized by orthogonal adaptive meshes, which place additional points where large gradients occur and a procedure to...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2960247
更新日期:2008-09-01 00:00:00
abstract::A scintillation dosemeter is calibrated for 90Sr/90Y beta rays from an ophthalmic applicator, using an extrapolation ionization chamber as a reference instrument. The calibration factor for the scintillation dosemeter agrees with that given by the manufacturer of the dosemeter within ca. 2%. The estimated overall unce...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1709490
更新日期:2004-05-01 00:00:00
abstract::Modern linear accelerators contain multiple isocentres, defined by the mechanical motions of gantry, collimator and table. Isocentre localization for these motions has been performed using film and manual evaluations which have difficulty in relating the individual motions. To address these limitations, we have develo...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2965950
更新日期:2008-07-01 00:00:00
abstract:PURPOSE:Automated 3D breast ultrasound (ABUS) has gained interest in breast imaging. Especially for screening women with dense breasts, ABUS appears to be beneficial. However, since the amount of data generated is large, the risk of oversight errors is substantial. Computer aided detection (CADe) may be used as a secon...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4914162
更新日期:2015-04-01 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
abstract:PURPOSE:Mega-voltage cone-beam CT (MVCBCT) imaging can be used to monitor changes in neck flexion and calculate the true spinal cord dose during radiotherapy. To sum the dose over multiple fractions and compare with the planned dose requires deformable image registration. This study investigates the accuracy of deforma...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4734919
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:Magnetic resonance imaging (MRI) is increasingly used for radiotherapy target delineation, image guidance, and treatment response monitoring. Recent studies have shown that an entire external x-ray radiotherapy treatment planning (RTP) workflow for brain tumor or prostate cancer patients based only on MRI refer...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4958677
更新日期:2016-08-01 00:00:00
abstract::Two new liquid ionization chamber (LIC) designs, consisting of cylindrical and plane-parallel configurations, are presented. They are designed to be suitable for high-precision measurements of absorbed dose-to-water at dose rates and photon energies typical for LDR intermediate photon energy brachytherapy sources. The...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598268
更新日期:1998-06-01 00:00:00
abstract::A number of relocatable head fixation systems have become commercially available or developed in-house to perform fractionated stereotactic radiotherapy (SRT) treatment. The uncertainty usually quoted for the target repositioning in SRT is over 2 mm, more than twice that of stereotactic radiosurgery (SRS) systems. Thi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598930
更新日期:2000-04-01 00:00:00
abstract::Encapsulated, cylindrical sources containing 2, 5, and 8 Ci of 241Am have been designed and fabricated for intracavitary irradiation of uterine cancers. Exposure rates in air and dose rates in water around these sources have been measured using an ionization chamber and a lithium fluoride thermoluminescent dosimetry s...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.596007
更新日期:1987-09-01 00:00:00
abstract:PURPOSE:Timely identification of systematic changes in radiation delivery of an imaging system can lead to a reduction in risk for the patients involved. However, existing quality assurance programs involving the routine testing of equipment performance using phantoms are limited in their ability to effectively carry o...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3524224
更新日期:2011-01-01 00:00:00
abstract::The paper presents a theoretical derivation of the photon fluence simulation efficiency in photon beam treatment head simulations without and with bremsstrahlung splitting. The expressions obtained provide a rigorous explanation of the efficiency dependence on scoring zone size and splitting number and explain the lar...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1943808
更新日期:2005-07-01 00:00:00
abstract::The purpose of this paper is to develop a method that reduces the number of segments for intensity modulated arc therapy (IMAT) and intensity modulated radiotherapy (IMRT) for concave target volumes (TV). The aim was to utilize no more than two intensity levels per organ at risk (OAR) and to derive both optimal segmen...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1861161
更新日期:2005-03-01 00:00:00
abstract::The effects of small cavities on dose in water and the dose in a homogeneous nonunit density medium illustrate that inhomogeneities do not act independently in photon dose perturbation, and serve as two constraints which should be satisfied by approximate methods of computed tomography (CT) pixel-based dose calculatio...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595294
更新日期:1983-03-01 00:00:00
abstract:PURPOSE:Planning for the delivery of intensity-modulated radiation therapy (IMRT) to a moving target, referred to as four-dimensional (4D) IMRT planning, is a crucial step for achieving the treatment objectives for sites that move during treatment delivery. The authors proposed a simplistic method that accounts for bot...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.3319498
更新日期:2010-05-01 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
abstract:PURPOSE:Radiosurgery uses small fields and high-radiation doses to treat intra- and extracranial lesions in a single session. The lack of a lateral electronic equilibrium and the presence of high-dose gradients in these fields are challenges for adequate measurements. The availability of radiation detectors with the hi...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4752211
更新日期:2012-10-01 00:00:00
abstract:PURPOSE:Colitis refers to inflammation of the inner lining of the colon that is frequently associated with infection and allergic reactions. In this paper, we propose deep convolutional neural networks methods for lesion-level colitis detection and a support vector machine (SVM) classifier for patient-level colitis dia...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12399
更新日期:2017-09-01 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:A series of examples are presented in which potential errors in the delivery of radiation therapy were prevented through use of incident learning. These examples underscore the value of reporting near miss incidents. METHODS:Using a departmental incident learning system, eight incidents were noted over a two-y...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4760774
更新日期:2012-11-01 00:00:00
abstract::The relatively precise placement of brachytherapy sources afforded by stereotactic frames for brain implants is not generally achievable for other sites, which lack the fixed geometry of the cranium and its contents. An exception is a source-containing rigid mold that delivers brachytherapy when inserted securely in a...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597454
更新日期:1995-03-01 00:00:00
abstract::The purpose of this work is to compare the efficacy of mathematical models in predicting the occurrence of radiotherapy-induced left ventricular perfusion defects assessed using single-photon emission computed tomography (SPECT). The basis of this study is data from 73 left-sided breast/ chestwall patients treated wit...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1823571
更新日期:2005-01-01 00:00:00
abstract::Accurate dosimetry of small-field photon beams tends to be difficult to perform due to the presence of lateral electronic disequilibrium and steep dose gradients. In stereotactic radiosurgery (SRS), small fields of 6-30 mm in diameter are used. Generally thermoluminescence dosimetry chips, Farmer, Thimble ion chamber,...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1350437
更新日期:2001-03-01 00:00:00
abstract:PURPOSE:To investigate the effect of energy (kVp) and filters (no filter, half Bowtie, and full Bowtie) on the dose response curves of the Gafchromic XRQA2 film and nanoDot optical stimulated luminescence dosimeters (OSLDs) in CBCT dose fields. To measure surface and internal doses received during x-ray volume imager (...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4803466
更新日期:2013-06-01 00:00:00