bluuebunny/crossref_metadata_2025_split huggingface dataset:
EGSnrc‐based Monte Carlo dosimetry of CSA1 and CSA2 brachytherapy source models
Authors: Selvam T. Palani , Sahoo S. , Vishwakarma R. S. 
Published: August 2009

Purpose:AAPM TG‐56 recommends the use of a specific dosimetric dataset for each brachytherapy source model. In this study, a full dosimetric dataset for indigenously developedsource models, namely, the CSA1 and CSA2, in accordance with the AAPM TG‐43U1 formalism is presented. The study includes calculation of dose‐to‐kerma ratioin water around these sources including stainless steel encapsulatedsources such as RTR, 3M, and selectron/LDR.Methods:The Monte Carlo–based EGSnrcMP code system is employed for modeling the sources in vacuum and in water. Calculations of air‐kerma strength,for the investigated sources and collision kerma in water along the transverse axis of the RTR source are based on the FLURZnrc code. Simulations of water‐kerma and dose in water for the CSA1, CSA2, RTR, 3M, and selectron/LDRsources are carried out using the DOSRZnrc code. In DOSRZnrc calculations, water‐kerma and dose are scored in a cylindrical water phantom having dimensions of.Results:The calculated dose‐rate constants for the CSA1 and CSA2 sources are 0.945(1) and 1.023(1) cGy/(h U), respectively. The calculated value ofper unit source activity,for the CSA1 and CSA2 sources is. The EGSnrcMP‐based collision kerma rates for the RTR source along the transverse axis (0.25–10 cm) agree with the correspondingGEANT4‐based published values within 0.5%. Anisotropy profiles of the CSA1 and CSA2 sources are significantly different from those of other sources. For the selectron/LDR single pelletspherical source (modeled as a cylindrical pellet with dimensions similar to the seed selectron), the values ofat 1 and 1.25 mm from the capsule are 1.023(1) and 1.029(1), respectively. The value ofat 1 mm from the CSA1, CSA2, RTR, and 3Msource capsules (all sources have an external radius of 1.5 mm) is 1.017(1) and this ratio is applicable to axial positionsto. This is in contrast to a publishedGEANT4‐based Monte Carlo dosimetric study on RTR and 3Msources wherein the authors have assumed that collision kerma is approximately equal to absorbed dose at 1 mm from the source capsules. Collision kerma is approximately equal to absorbed dose for distancesfrom source capsules as opposed toreported in published studies. A detailed electron transport is necessary up to 2 mm from source capsules.Conclusions:The Monte Carlo–calculated dose‐rate data for the CSA1 and CSA2 sources can be used as input data for treatment planning or to verify the calculations by radiotherapy treatment planning system.
A general analytical solution to the geometrical problem of field matching in radiotherapy
Authors: Hernandez V. , Arenas M. , Pons F. , Sempau J. 
Published: August 2009

Purpose:Several authors studied the problem of geometrical matching of fields produced by medical linear accelerators. However, a general solution has yet to be published. Currently available solutions are based on parallelism arguments. This study provides a general solution, considering not only parallelism but also field sizes.Methods:A fixed field with arbitrary field size, gantry, collimator, and couch angle is considered, and another field with a fixed gantry angle is matched to it. A single reference system attached to the treatment couch is used, and two approaches are followed. In the first approach, fixed field sizes are assumed and parallelism of the adjacent field‐side planes is imposed. In the second approach, fixed isocenter positions are considered and both parallelism and coincidence between field‐side planes are required.Results:When fixed field sizes are assumed, rotation angles are obtained; however, the isocenters may need to be shifted to make side planes coincident and therefore achieve a proper match. When fixed isocenter positions are considered, solutions for all parameters, including the field size, are obtained and an exact geometrical match is achieved.Conclusions:General expressions to the field‐matching problem are found for the two approaches followed, fixed field sizes, and fixed isocenter positions. These results can be applied to any treatment technique and can easily be implemented in modern treatment planning systems.
Scintillator avalanche photoconductor with high resolution emitter readout for low dose x‐ray imaging: Lag
Authors: Li Dan , Zhao Wei , Nanba Masakazu , Egami Norifomi 
Published: August 2009

Purpose:A new concept of indirect conversion flat‐panel imager with avalanche gain and field emitter array (FEA) readout is being investigated. It is referred to as scintillator avalanche photoconductor with high resolution emitter readout (SAPHIRE). The present work investigates the temporal performance, i.e., lag, of SAPHIRE.Methods:Since the temporal performance of the x‐ray detection materials, i.e., the structured scintillator and avalanche amorphous selenium photoconductor, has been studied previously, the investigation is focused on lag due to the FEA readout method. The principle of FEA readout is similar to that of scanning electron beam readout used in camera tubes, where the dominant source of lag is the energy spread of electrons. Since the principles of emission and beam focusing methods for FEA are different from thermionic emission used in camera tubes, its electron beam energy spread and hence lag is expected to be different. In the present work, the energy spread of the electrons emitted from a FEA was investigated theoretically by analyzing different contributing factors due to the FEA design and operations: The inherent energy spread of field emission, the FEA driving pulse delay, and the angular distribution of emitted electrons. The electron energy spread determined the beam acceptance characteristic curve of the photoconductive target, i.e., the accepted beam current as a function of target potential , from which lag could be calculated numerically. Lag calculation was performed using FEA parameters of two prototype HARP‐FEA image sensors, and the results were compared with experimental measurements. Strategies for reducing lag in SAPHIRE were proposed and analyzed.Results:The theoretical analysis shows that the dominant factor for lag is the angular distribution of electrons emitted from the FEA. The first frame lags for two prototype sensors with 4 and HARP layer thicknesses were 62.1% and 9.1%, respectively. A lag clearance procedure can be implemented by turning on all the FEA pixels simultaneously between subsequent frames without negative impact of readout speed. For large‐area SAPHIRE, the bias electrode for the HARP needs to be divided into strips to allow parallel readout. With typical cardiac detector parameters, SAPHIRE with 128 parallel strips can provide real‐time readout (30 frames/s) with first frame lag of .Conclusions:The investigation of lag in SAPHIRE shows that the angular distribution of emitted electrons from FEA can result in substantial lag if the readout was performed pixel by pixel. Effective strategies for reducing lag include dividing the bias electrode into multiple strips to allow parallel readout and the incorporation of rapid charge clearance procedure between subsequent frames or rows.
Spatial analysis of magnetic resonance and relaxation times improves classification between subjects with and without osteoarthritis
Authors: Carballido‐Gamio Julio , Stahl Robert , Blumenkrantz Gabrielle , Romero Adan , Majumdar Sharmila , Link Thomas M. 
Published: August 2009

Purpose:Studies have shown that functional analysis of knee cartilage based on magnetic resonance (MR) relaxation times is a valuable tool in the understanding of osteoarthritis (OA). In this work, the regional spatial distribution of knee cartilage and relaxation times based on texture and laminar analyses was studied to investigate if they provide additional insight compared to global mean values in the study of OA.Methods:Knee cartilage of 36 subjects, 19 healthy controls and 17 with mild OA, was divided into 16 compartments. and relaxation times were studied with first order statistics, eight texture parameters with four different orientations using gray‐level co‐occurrence matrices and by subdividing each compartment into two different layers: Deep and superficial. Receiver operating characteristic curve analysis was performed to evaluate the potential of each technique to correctly classify the populations.Results:Although the deep and superficial cartilage layers had in general significantly different and relaxation times, they performed similarly in terms of subject discrimination. The subdivision of lateral and medial femoral compartments into weight‐bearing and non‐weight‐bearing regions did not improve discrimination. Also it was found that the most sensitive region was the patella and that discriminated better than . The most important finding was that with respect to global mean values, laminar and texture analyses improved subject discrimination.Conclusions:Results of this study suggest that spatially assessing MR images of the knee cartilage relaxation times using laminar and texture analyses could lead to better and probably earlier identification of cartilage matrix abnormalities in subjects with OA.
On the speckle‐free nature of photoacoustic tomography
Authors: Guo Zijian , Li Li , Wang Lihong V. 
Published: August 2009

Purpose:A long‐standing conundrum is why photoacoustic tomography (PAT) possesses the unique ability to produce images devoid of speckle artifacts while all other coherent imaging technologies do not.Methods:In this paper, we explain the inherent mechanism that suppresses speckle in PAT, and the analysis was validated by simulations based on an experimental PAT system.Results:We found that the speckle‐free feature of PAT results directly from the optical absorption contrast.Conclusions:All optical absorbers expand on laser excitation, and therefore all initial photoacoustic pressure rises are positive, which engenders strong correlations among the photoacoustic waves from the absorbers. As a result, prominent boundaries always build up in photoacoustic images and suppress the interior speckle.
Monte Carlo model for a prototype CT‐compatible, anatomically adaptive, shielded intracavitary brachytherapy applicator for the treatment of cervical cancer
Authors: Price Michael J. , Gifford Kent A. , Horton John L. , Eifel Patricia J. , Gillin Michael T. , Lawyer Ann A. , Mourtada Firas 
Published: August 2009

Purpose:Current, clinically applicable intracavitary brachytherapy applicators that utilize shielded ovoids contain a pair of tungsten‐alloy shields which serve to reduce dose delivered to the rectum and bladder during source afterloading. After applicator insertion, these fixed shields are not necessarily positioned to provide optimal shielding of these critical structures due to variations in patient anatomies. The authors present a dosimetric evaluation of a novel prototype intracavitary brachytherapy ovoid [anatomically adaptive applicator], featuring a single shield whose position can be adjusted with two degrees of freedom: Rotation about and translation along the long axis of the ovoid.Methods:The dosimetry of the device for a HDR was characterized using radiochromic film measurements for various shield orientations. A MCNPX Monte Carlo model was developed of the prototype ovoid and integrated with a previously validated model of a v2 mHDR source (Nucletron Co.). The model was validated for three distinct shield orientations using film measurements.Results:For the most complex case, 91% of the absolute simulated and measured dose points agreed within 2% or and 96% agreed within 10% or .Conclusions:Validation of the Monte Carlo model facilitates future investigations into any dosimetric advantages the use of the may have over the current state of art with respect to optimization and customization of dose delivery as a function of patient anatomical geometries.
Evaluation of high‐energy brachytherapy source electronic disequilibrium and dose from emitted electrons
Authors: Ballester Facundo , Granero Domingo , Pérez‐Calatayud José , Melhus Christopher S. , Rivard Mark J. 
Published: August 2009

Purpose:The region of electronic disequilibrium near photon‐emitting brachytherapy sources of high‐energy radionuclides (, , , and ) and contributions to total dose from emitted electrons were studied using the GEANT4 and PENELOPE Monte Carlo codes.Methods:Hypothetical sources with active and capsule materials mimicking those of actual sources but with spherical shape were examined. Dose contributions due to source photons, x rays, and bremsstrahlung; source , Auger electrons, and internal conversion electrons; and water collisional kerma were scored. To determine if conclusions obtained for electronic equilibrium conditions and electron dose contribution to total dose for the representative spherical sources could be applied to actual sources, the mHDR‐v2 source model (Nucletron B.V., Veenendaal, The Netherlands) was simulated for comparison to spherical source results and to published data.Results:Electronic equilibrium within 1% is reached for, , , and at distances greater than 7, 3.5, 2, and 1 mm from the source center, respectively, in agreement with other published studies. At 1 mm from the source center, the electron contributions to total dose are 1.9% and 9.4% for and , respectively. Electron emissions become important (i.e., ) within 3.3 mm of and 1.7 mm of sources, yet are negligible over all distances for and . Electronic equilibrium conditions along the transversal source axis for the mHDR‐v2 source are comparable to those of the spherical sources while electron dose to total dose contribution are quite different.Conclusions:Electronic equilibrium conditions obtained for spherical sources could be generalized to actual sources while electron contribution to total dose depends strongly on source dimensions, material composition, and electron spectra.
Monte Carlo simulation and patient dosimetry for a kilovoltage cone‐beam CT unit
Authors: Downes P. , Jarvis R. , Radu E. , Kawrakow I. , Spezi E. 
Published: August 2009

Purpose:The purpose of this work is to characterize the x‐ray volume imager (XVI), the cone‐beam computed tomography (CBCT) unit mounted on the Elekta Synergy linac, with F1 bowtie filter and to calculate the three‐dimensional dose delivered to patients using volumetric acquisition.Methods:The XVI is modeled in detail using a new Monte Carlo (MC) code,BEAMPP, under development at the National Research Council Canada. In this investigation, a new component module is developed to accurately model the unit's bowtie filter used in conjunction with the available beam collimators at the clinical energy of. The modeling is compared against percentage depth dose (PDD) and profile measurements. Kilovoltage radiation beams’ phase space files are also analyzed. The authors also describe a method for the absolute dose calibration of the MC model of the CBCT unit when used in a clinical volumetric acquisition mode. Finally, they calculate three‐dimensional patient dose from CBCT image acquisition in three clinical cases of interest: Pelvis, lung, and head and neck.Results:The agreement between measurement and MC is shown to be very good: Withinfor the PDD and withininside the radiation field for all the collimators with the F1 bowtie filter. A full account of the absolute calibration method is given and dose calculation is validated against ion chamber measurements in different locations of a plastic phantom. Calculations and experiments agree withinor better in both at the center and the periphery of the phantom, with worst agreement of 4.5% at the surface of the phantom and for one specific combination of collimator and filter. Patient dose from CBCT scan reveals that dose to tissue is between 2 andfor a pelvis or a lung full acquisition. For H&N dose to tissue is, with the unit presets used in this work. Dose to bony structures can be two to three times higher than dose to tissue.Conclusions:The XVI CBCT unit has been fully modeled including the F1 bowtie filter. Absolute dose distribution from the unit has been successfully validated. Full MC patient dose calculation has shown that the three‐dimensional dose distribution from CBCT is complex. Patient dose from CBCT exposure cannot be completely accounted for by using a numerical factor as an estimate of the dose at the center of the body. Furthermore, additional dose to bone should be taken into account when adopting any IGRT strategy and weighed vs the unquestionable benefits of the technique in order to optimize treatment. Full three‐dimensional dose calculation is recommended if patient dose from CBCT is to be integrated in any adaptive planning strategy.
Argon and nitrogen adsorption on graphite at high temperatures
Authors: Bottani Eduardo Jorge , Llanos Jorge Luis , Cascarini de Torre Lydia Ethel 
Published: August 2009

Nitrogen and argon adsorption on two graphites differing in their surface homogeneity was studied in a wide range of temperatures (77.5 K up to 183.2 K). The experimentally determined entropy of the adsorbed phase and isoteric heat of adsorption were analyzed. The Hill-de Boer adsorption isotherm was employed to calculate the apparent two-dimensional critical temperature. The behaviour of the adsorbed film was analyzed to explain the influence exerted upon it by temperature and surface homogenity.
Use of inhibited enzyme electrode for estimation of PEA diamine oxidase inhibitors
Authors: Macholán Lumír , Slanina Jiří 
Published: August 2009

A biosensor consisting of a Clark type oxygen electrode and immobilized pea diamine oxidase makes it possible amperometrically to quantify, on the basis of an inhibition effect, substrate analogues of the enzyme (aliphatic amino ketones and monoamines, aromatic diamines), some alkaloids (cinchonine, lobeline, norsedamine) and drugs (1-phenylcyclopropylamine, naphazoline). The output current signal of the inhibited bioelectrode is influenced by the thickness of the membrane and its enzyme content as well as by the sort of the substrate and oxygen concentration in the reaction medium. With most of the tested substances, the response time τ90 is 20-100 s and the linear concentration range about 10-6-10-3 mol l-1 can be observed. The inhibitor concentrations causing a change of the initial current by 50% correspond mostly to the published values of inhibition constants for soluble enzyme. The most efficient inhibitor of the pea diamine oxidase is 1,5-diamino-3-pentanone, for which the accuracy of the method was 5.6%, its reproducibility 7.2%, and detection limit 5 . 10-9 mol l-1.
Formation of sodium disulfite in a solid-gas system
Authors: Vobiš Jiří , Mocek Karel , Erdös Emerich 
Published: August 2009

The formation of sodium disulfite by the heterogeneous reaction of solid active sodium sulfite with gaseous sulfur dioxide in the presence of water vapour was investigated over the temperature range of 293 to 393 K at SO2. H2O and O2 partial pressures of 1.2-7.4, 1.2-6.4 and 0-11.3 kPa, respectively. The effect of the reaction time was also examined. Kinetic measurements were supplemented with the determination of the equilibrium dissociation pressure of SO2 in contact with sodium sulfite at 373.15 K. The major aim of the work was to establish the optimum conditions for attaining the maximum degree of conversion of the solid reactant to sodium disulfite. The conditions for the formation of virtually pure sodium disulfite were found.
Would you sell a kidney in a regulated kidney market? Results of an exploratory study
Authors: Rid A , Bachmann L M , Wettstein V , Biller-Andorno N 
Published: August 2009

Background:It is often claimed that a regulated kidney market would significantly reduce the kidney shortage, thus saving or improving many lives. Data are lacking, however, on how many people would consider selling a kidney in such a market.Methods:A survey instrument, developed to assess behavioural dispositions to and attitudes about a hypothetical regulated kidney market, was given to Swiss third-year medical students.Results:Respondents’ (n = 178) median age was 23 years. Their socioeconomic status was high or middle (94.6%). 48 (27%) considered selling a kidney in a regulated kidney market, of whom 31 (66%) would sell only to overcome a particularly difficult financial situation. High social status and male gender was the strongest predictor of a disposition to sell. 32 of all respondents (18%) supported legalising a regulated kidney market. This attitude was not associated with a disposition to sell a kidney. 5 respondents (2.8%) endorsed a marketandconsidered providing a kidney to a stranger if and only if paid. 4 of those 5 would sell only under financial duress.Conclusions:Current understanding of a regulated kidney market is insufficient. It is unclear whether a regulated market would result in a net gain of kidneys. Most possible kidney vendors would only sell in a particularly difficult financial situation, raising concerns about the validity of consent and inequities in the provision of organs. Further empirical and normative analysis of these issues is required. Any calls to implement and evaluate a regulated kidney market in pilot studies are therefore premature.
Ethical analysis of the justifiability of labelling with COPD for smoking cessation
Authors: Kotz D , Vos R , Huibers M J H 
Published: August 2009

Background:Spirometry for early detection of chronic obstructive pulmonary disease (COPD) and smoking cessation is criticised because of the potential negative effects of labelling with disease.Aim:To assess the effects of opinions of smokers with mild to moderate COPD on the effectiveness of spirometry for smoking cessation, the justification of early detection of airflow limitation in smokers and the impact of confrontation with COPD.Design:Qualitative study with data from a randomised controlled trial.Setting:General population of Dutch and Belgian Limburg.Methods:Semistructured ethical exit interviews were conducted with 205 smokers who were motivated to quit smoking and had no prior diagnosis of COPD but were detected with airflows limitation by means of spirometry. They received either (1) counselling, including labelling with COPD, plus with nortriptyline for smoking cessation, (2) counselling excluding labelling with COPD, plus nortriptyline for smoking cessation or (3) care as usual for smoking cessation by the general practitioner, without labelling with COPD.Results:Of the participants, 177 (86%) agreed or completely agreed that it is justified to measure lung function in heavy smokers. These participants argued that measuring lung function raises consciousness of the negative effects of smoking, helps to prevent disease or increases motivation to stop smoking. Most of the 18 participants who disagreed argued that routinely measuring lung function in smokers would interfere with freedom of choice.Conclusions:Labelling with disease is probably a less important issue in the discussion about the pros and cons of early detection of COPD.