Abstract:
:Current dosimetry protocols for clinical protons do not take into account any secondary electron fluence perturbation in ion chambers. In this work, we performed a systematic study of secondary electron fluence perturbation factors for spherical and cylindrical ion chambers in proton beams (70-250 MeV). The electron fluence perturbation factor, pe, was calculated using Monte Carlo transport of protons and secondary electrons. The influence of proton energy, cavity wall material (graphite, water, A150, PMMA, polystyrene), cavity radius, cavity wall thickness and positioning depth in water is studied. The influence of inelastic nuclear proton interactions is briefly discussed. It was found that pe depends on wall material; the largest values for pe were obtained for ion chambers with A150 walls (pe=1.009), the smallest values for graphite walls. The perturbation factor was found to be largely independent of proton energy. A slight decrease of pe with cavity radius was obtained, especially for low energy protons. The wall thickness was found to have no effect on pe in the range studied (0.025-0.1 cm). The depth of the cavity in a water phantom was also found to have an insignificant effect on pe. Based on the results in the paper for spherical and cylindrical ion chambers, a method to calculate pe for a thimble ion chamber is presented. The results presented in this paper for cylindrical and spherical ion chambers are in contradiction to the calculated electron fluence perturbation factors for planar ion chambers in the paper by Casnati et al.
journal_name
Med Physjournal_title
Medical physicsauthors
Verhaegen F,Palmans Hdoi
10.1118/1.1406519subject
Has Abstractpub_date
2001-10-01 00:00:00pages
2088-95issue
10eissn
0094-2405issn
2473-4209journal_volume
28pub_type
杂志文章相关文献
MEDICAL PHYSICS文献大全abstract::A commercial optical system developed by Solid Photography, Inc., has been used to generate precise paraffin--polyethylene tissue compensators. A program with the objective of constructing a medical facility has been undertaken to access patient topology for treatment planning, tissue-compensator fabrication, and pati...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594447
更新日期:1978-11-01 00:00:00
abstract::Current generation electronic portal imaging devices (EPID) contain a 1.0 mm copper conversion plate to increase detection efficiency of a therapeutic megavoltage spectrum. When using these EPIDs for low-Z target imaging, the conversion plate largely attenuates the large populations of diagnostic energy photons, there...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4740105
更新日期:2012-07-01 00:00:00
abstract:PURPOSE:Radiosensitizer enhanced radiotherapy provides the possibility of improved treatment outcomes by preferentially increasing the effectiveness of radiation within the tumor. Proton therapy offers improved sparing of tissue distal of the tumor along the beam path and reduced integral dose compared to conventional ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13923
更新日期:2020-02-01 00:00:00
abstract::When a beam-modifying filter such as a wedge or a compensator is placed in an x-ray beam, scattered photons are generated in the filter material. The magnitude of the dose contribution from these photons for a 4-MV x-ray beam was measured. At a distance of 30 cm from the filter, a copper sheet of 1-cm thickness produc...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.595923
更新日期:1986-01-01 00:00:00
abstract:PURPOSE:Monte Carlo (MC) dose calculation is generally superior to analytical dose calculation (ADC) used in commercial TPS to model the dose distribution especially for heterogeneous sites, such as lung and head/neck patients. The purpose of this study was to provide a validated, fast, and open-source MC code, MCsquar...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.13231
更新日期:2018-12-01 00:00:00
abstract:PURPOSE:To evaluate dosimetric variations of planning target volume (PTV) on critical organs such as rectal wall, bladder and femoral head, when the patient size changes due to weight loss in prostate volumetric modulated arc therapy (VMAT). METHODS:Three patients with small (32.0 cm3 ), medium (48.4 cm3 ) and large (...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4735610
更新日期:2012-06-01 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::The nucletron Leipzig applicator is designed for (HDR) 192Ir brachy radiotherapy of surface lesions. The dosimetric characteristics of this applicator were investigated using simulation method based on Monte Carlo N-particle (MCNP) code and phantom measurements. The simulation method was validated by comparing calcula...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1812609
更新日期:2004-12-01 00:00:00
abstract::Currently, patients with brain neoplasms must undergo both computed tomography (CT) and magnetic resonance (MR) imaging to take advantage of CT's density information and MR's soft tissue imaging capabilities. A method has been developed that allows virtual simulation, digitally reconstructed radiographs (DRRs), and 3-...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598382
更新日期:1998-10-01 00:00:00
abstract:PURPOSE:The outcome of radiotherapy can be further improved by combining irradiation with dose enhancers such as high-Z nanoparticles. Since 2004, spectacular results have been obtained when low-energy x-ray irradiations have been combined with nanoparticles. Recently, the same combination has been explored in hadron t...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4934370
更新日期:2015-11-01 00:00:00
abstract::Cone-beam computed tomography systems have been developed to provide in situ imaging for the purpose of guiding radiation therapy. Clinical systems have been constructed using this approach, a clinical linear accelerator (Elekta Synergy RP) and an iso-centric C-arm. Geometric calibration involves the estimation of a s...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1869652
更新日期:2005-04-01 00:00:00
abstract:PURPOSE:The biologically effective dose (BED) of temporary brachytherapy treatments is a function of both chosen radionuclide (R) and implant duration (T). This study endeavored to evaluate BED delivered to the tumor volume and surrounding ocular structures as a function of plaque position (P), prescription dose, R, an...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4735548
更新日期:2012-06-01 00:00:00
abstract::Clinical and biological evidence suggest that the success of GRID therapy in debulking large tumors depends on the high peak-to-valley contrast in the dose distribution. In this study, we show that the peaks and valleys can be significantly blurred out by respiration-induced tumor motion, possibly affecting the clinic...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2977538
更新日期:2008-10-01 00:00:00
abstract::The Anisotropic Analytical Algorithm (AAA) of the Varian Eclipse treatment planning system calculates absolute dose for a variety of beam settings including those with an enhanced dynamic wedge (EDW). This algorithm has gone through a number of version updates since it was first released in July 2005. Previous version...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2965929
更新日期:2008-07-01 00:00:00
abstract::Monte Carlo calculations have been performed for the purpose of characterizing the dosimetric properties of three brachytherapy sources. The three sources are manufactured by Syncor Pharmaceuticals Inc. and consist of two 125I seeds (BT-125-1 and BT-125-2) and one 103Pd seed (BT-103-3). The BT-125-1 and BT-125-2 seed ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.1469627
更新日期:2002-05-01 00:00:00
abstract::Generating an optimized radiation treatment plan requires understanding the factors affecting tumour control. Mathematical models of tumour dynamics may help in future studies of factors predicting tumor sensitivity to radiotherapy. In this study, a time-dependent differential model, incorporating biological cancer ma...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.2965923
更新日期:2008-07-01 00:00:00
abstract:PURPOSE:The purpose of this study is to evaluate the feasibility of kilovoltage cone-beam CT (CBCT) images that are obtained with the Varian On-Board Imager in dose calculation at each radiation therapy. METHODS:CBCT images are commonly degraded by scattered radiations originating in the patient's body, and so the CT ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4734936
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::A contrast-detail (CD) experiment was performed to study the effect of lossy compression on computed radiographic (CR) images. Digital CR images of a phantom were compressed by quantizing the full-frame discrete cosine transform and Huffman encoding the result. Since low-contrast detectability is directly linked to an...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.597489
更新日期:1995-06-01 00:00:00
abstract:PURPOSE:The objectives of this study were (a) to devise a technique for measuring quantum noise in clinical body computed tomography (CT) images and (b) to develop a model for predicting that noise with high accuracy. METHODS:The study included 83 clinical image sets at two dose levels (clinical and 50% reduced dose l...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4938588
更新日期:2016-01-01 00:00:00
abstract::A realistic photon beam model based on Monte Carlo simulation of clinical linear accelerators was implemented in a convolution/superposition dose calculation algorithm. A primary and an extra-focal sources were used in this beam model to represent the direct photons from the target and the scattered photons from other...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598111
更新日期:1997-12-01 00:00:00
abstract:PURPOSE:To evaluate a model which can predict patient's Entrance Skin Exposure (ESE) from height and weight and a single kVp mR/mAs measurement for radiographic. METHODS:Patient height, weight and post exposure mAs are obtained to assess ESE based on IAEA model. Patient's thickness is obtained by assuming a cylindrica...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4734825
更新日期:2012-06-01 00:00:00
abstract:PURPOSE:Flattening filters (FFs) have been considered as an integral part of the treatment head of a medical accelerator for more than 50 years. The reasons for the longstanding use are, however, historical ones. Advanced treatment techniques, such as stereotactic radiotherapy or intensity modulated radiotherapy have s...
journal_title:Medical physics
pub_type: 杂志文章,评审
doi:10.1118/1.3554643
更新日期:2011-03-01 00:00:00
abstract::The method of images is employed to insert the effects of the presence of a single lateral boundary on contrast functions previously derived for an infinite slab using a random walk model of photon transport. The predictions of the model for zero and extrapolated boundary conditions are compared with Monte Carlo (MC) ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.598687
更新日期:1999-09-01 00:00:00
abstract:PURPOSE:The purpose of this study was to investigate the potential of MR-guided pulsed focused ultrasound (pFUS) for the enhancement of drug uptake in prostate tumors in vivo using doxorubicin (Dox). METHODS:An antitumor drug Dox, an orthotopic animal prostate tumor model using human prostate cancer, LNCaP cell line, ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4705346
更新日期:2012-05-01 00:00:00
abstract:PURPOSE:Cone beam computed tomography (CBCT) suffers from a large amount of scatter, resulting in severe scatter artifacts in the reconstructions. Recently, a new scatter correction approach, called improved primary modulator scatter estimation (iPMSE), was introduced. That approach utilizes a primary modulator that is...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1002/mp.12094
更新日期:2017-09-01 00:00:00
abstract:PURPOSE:To build a statistical model to quantitatively correlate the anatomic features of structures and the corresponding dose-volume histogram (DVH) of head and neck (HN) Tomotherapy (Tomo) plans. To study if the model built upon one intensity modulated radiation therapy (IMRT) technique (such as conventional Linac) ...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4828788
更新日期:2013-12-01 00:00:00
abstract:PURPOSE:To evaluate the energy dependence of Gafchromic EBT3 film for establishing a quality assurance method of bolus electron conformal radiotherapy. METHODS:We irradiated electron beam to EBT3 films, which were set in the water tank. The linear accelerator used was Varian Clinac 21EX. The energy of electron beams w...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.4735200
更新日期:2012-06-01 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::We have recently installed a linear accelerator, modified to allow computer control of several machine parameters during irradiation of the patient. As an initial feasibility study of computer-controlled radiation therapy, its application to produce wedge-shaped dose distributions by moving the collimator jaws has bee...
journal_title:Medical physics
pub_type: 杂志文章
doi:10.1118/1.594440
更新日期:1978-09-01 00:00:00