bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulation of the precision limits of plastic scintillation detectors using optimal component selection
Authors: Lacroix Frédéric , Beaulieu Luc , Archambault Louis , Beddar A. Sam 
Published: January 2010

Purpose:The purpose of this work was threefold: First, to determine which type of charge‐coupled device (CCD) would provide the best dosimetric precision for plastic scintillation detectors (PSDs); second, to design a high‐photon‐efficiency PSD system by optimizing its signal‐to‐noise ratio (SNR) using off‐the‐shelf technology; and third, to establish the spatial, temporal, and dose precision limits of such a PSD system. The authors have attempted to design a dosimetric tool suitable for radiotherapy treatment modalities employing small fields or fast temporal modulation of the radiation fields, and to explore the current precision limits of PSD systems.Methods:The authors used an SNR simulation model to design and calculate the dosimetric precision of a PSD employing a fiber taper to couple the optical fiber to the photodetector. The authors also used the SNR simulation model to evaluate the impact of the photodetector performance characteristics on the SNR and to establish the spatial, temporal, and dose precision limits.Results:The authors found that a high‐photon‐efficiency PSD can provide a precision of 1% in of integration time for a dose rate of 400 cGy/min when a single image is taken, detect a dose of 1 cGy with a detector volume of , and image over 15 000 detectors with a precision of 1% on a CCD imaging area.Conclusions:These characteristics establish that PSDs theoretically constitute a suitable dosimetric tool for radiotherapy treatment modalities employing small fields or fast temporal modulation of the radiation fields.
Replacement correction factors for plane‐parallel ion chambers in electron beams
Authors: Wang Lilie L. W. , Rogers David W. O. 
Published: January 2010

Purpose:Plane‐parallel chambers are recommended by dosimetry protocols for measurements in (especially low‐energy) electron beams. In dosimetry protocols, the replacement correction factor is assumed unity for “well‐guarded” plane‐parallel chambers in electron beams when the front face of the cavity is the effective point of measurement. There is experimental evidence that ion chambers which are not well‐guarded (e.g., Markus) have nonunity values. Monte Carlo simulations are employed in this study to investigate the replacement correction factors for plane‐parallel chambers in electron beams.Methods:Using previously established Monte Carlo calculation methods, the values of are calculated with high statistical precision for the cavities of a variety of plane‐parallel chambers in a water phantom irradiated by various electron beams. The dependences of the values of on the beam quality, phantom depth, as well as the guard ring width are studied.Results:In the dose fall‐off region for low‐energy beams, the values are very sensitive to depth. It is found that this is mainly due to the gradient effect, which originates from the fact that the effective point of measurement for many plane‐parallel chambers should not be at the front face of the cavity but rather shifted toward the center of the cavity by a fraction of a millimeter. Using the front face of the cavity as the effective point of measurement, the calculated values of at are not unity for some well‐guarded plane‐parallel chambers. The calculated values for the Roos chamber are close to 1 for all electron beams. The calculation results for the Markus chamber are in good agreement with the measured values.Conclusions:The appropriate selection of the effective point of measurement for plane‐parallel chambers in electron beams is an important issue. If the effective point of measurement is correctly accounted for, the values would be almost independent of depth. Both the guard ring width and the ratio of the collecting volume diameter to the cavity thickness can influence the values of . For a diameter to thickness ratio of 5 (e.g., NACP02 chamber), the guard width has to be 6 mm for the chamber to be considered as well‐guarded, i.e., have a value of 1.00.
Optical spectroscopy of the breast in premenopausal women reveals tissue variation with changes in age and parity
Authors: Knight Julia A. , Blackmore Kristina M. , Wong Jody , Tharmalingam Sukirtha , Lilge Lothar 
Published: January 2010

Purpose:Variations during breast tissue development can influence later breast cancer risk. In particular, prolonged nulliparity increases risk. The authors used optical spectroscopy to compare breast tissue in 115 nulliparous women aged 31–40 (group 2) to 140 nulliparous women aged 18–21 (group 1), and also to 36 parous women aged 31–40 (group 3), and to evaluate the relationship between IGF‐1 and optical breast tissue properties. IGF‐1 has been linked in particular to premenopausal breast cancer.Methods:The authors measured the transmission spectra from 625 to 1050 nm wavelengths in each breast and determined regions of interindividual variation using principal components analysis. Spectral differences represent variation in lipid, water, oxyhemoglobin, deoxyhemoglobin, and collagen content. Group differences and the relationship with IGF‐1 were estimated by linear regression after adjustment for multiple factors including height, weight, ethnicity, hormonal contraceptive use, and days since last menstrual period.Results:Principal component 3 scores were more negative in the older nulliparous women compared to either younger nulliparous women or to parous women of the same age (, for group 2 vs group 1 and , for group 3 vs group 2). These differences appear to indicate increased deoxyhemoglobin relative to oxyhemoglobin content in the tissue of the older, nulliparous premenopausal women compared to the other groups, which may be an indicator of proportionally increased proliferative tissue. Principal component 4 also differed between older and younger nulliparous women (, for group 2 vs group 1) and was negatively associated with IGF‐1 in younger women (, ) and positively associated with IGF‐1 in older women (, ).Conclusions:Optical spectroscopy may be useful to identify breast tissue at increased risk of cancer development and track changes over time, particularly in young women where exposure to radiation is of particular concern. Additional work is needed to confirm the observed breast tissue differences and to determine the specific tissue chromophore changes with age and parity.
Dose‐rate distribution of ‐glass microspheres for intra‐arterial brachytherapy
Authors: Guimarães Carla C. , Moralles Maurício , Sene Frank F. , Martinelli José R. 
Published: January 2010

Purpose:The intra‐arterial administration of radioactive glass microspheres is an alternative therapy option for treating primary hepatocellular carcinoma, the main cause of liver cancer death, and metastatic liver cancer, another important kind of cancer induced in the liver. The technique involves the administration of radioactive microspheres in the hepatic artery, which are trapped preferentially in the tumor.Methods:In this work the GEANT4 toolkit was used to calculate the radial dose‐rate distributions in water from‐loaded glass microspheres and also from ‐loaded glass microspheres. To validate the toolkit for this application, the authors compared the dose‐rate distribution of and point sources in water with data from the International Commission on Radiation Units and Measurements report 72.Results:Tables of radial dose‐rate distributions are provided for practical use in brachytherapy planning with these microspheres.Conclusions:The simulations with the microspheres show that the shape of the beta ray energy spectra with respect to the and sources is significantly modified by the glass matrix.
Automated aortic calcium scoring on low‐dose chest computed tomography
Authors: Išgum Ivana , Rutten Annemarieke , Prokop Mathias , Staring Marius , Klein Stefan , Pluim Josien P. W. , Viergever Max A. , van Ginneken Bram 
Published: January 2010

Purpose:Thoracic computed tomography (CT) scans provide information about cardiovascular risk status. These scans are non‐ECG synchronized, thus precise quantification of coronary calcifications is difficult. Aortic calcium scoring is less sensitive to cardiac motion, so it is an alternative to coronary calcium scoring as an indicator of cardiovascular risk. The authors developed and evaluated a computer‐aided system for automatic detection and quantification of aortic calcifications in low‐dose noncontrast‐enhanced chest CT.Methods:The system was trained and tested on scans from participants of a lung cancer screening trial. A total of 433 low‐dose, non‐ECG‐synchronized, noncontrast‐enhanced 16 detector row examinations of the chest was randomly divided into 340 training and 93 test data sets. A first observer manually identified aortic calcifications on training and test scans. A second observer did the same on the test scans only. First, a multiatlas‐based segmentation method was developed to delineate the aorta. Segmented volume was thresholded and potential calcifications (candidate objects) were extracted by three‐dimensional connected component labeling. Due to image resolution and noise, in rare cases extracted candidate objects were connected to the spine. They were separated into a part outside and parts inside the aorta, and only the latter was further analyzed. All candidate objects were represented by 63 features describing their size, position, and texture. Subsequently, a two‐stage classification with a selection of features and‐nearest neighbor classifiers was performed. Based on the detected aortic calcifications, total calcium volume score was determined for each subject.Results:The computer system correctly detected, on the average, out of (97.9%) calcified plaque volume in the aorta with an average of of false positive volume per scan. Spearman rank correlation coefficient was between the system and the first observer compared to between the two observers.Conclusions:Automatic calcium scoring in the aorta thus appears feasible with good correlation between manual and automatic scoring.
Technical Note: Development of a tidal volume surrogate that replaces spirometry for physiological breathing monitoring in 4D CT
Authors: Werner René , White Benjamin , Handels Heinz , Lu Wei , Low Daniel A. 
Published: January 2010

Purpose:Spirometry exhibits baseline drift and frequent measurement errors so it cannot be used by itself to provide tidal volume‐based image sorting or breathing motion modeling. Other breathing surrogates, in this study an abdominal bellows system, are drift free but do not measure tidal volume. Simultaneously using spirometry and the bellows system allows the user to convert the recorded bellows signal to tidal volume but still relies on spirometry measurements. The authors therefore propose to use CT‐based air content, rather than a spirometer, to convert the bellows signal to tidal volume.Methods:41 4D CT data sets are acquired, while the breathing cycle is simultaneously measured using spirometry and an abdominal pressure bellows system. The assumptions underlying the conversion of the bellows measurement to tidal volume by CT‐based air content are analyzed. This comprises of detailed correlation studies of the spirometry‐measured tidal volume, the bellows signal, and CT‐based air content.Results:For patients, the spirometry signals are not consistently acquired during the 4D CT session, so correlating spirometry to bellows measurements and CT‐based air content leads to erroneous conversion coefficients. After introducing a minimum correlation threshold to remove these data, good correlations are obtained between the remaining breathing signals. The ratio of CT‐based air content to tidal volume is measured to be ; the expected value is 1.11 because room air is 11% more dense than air in the lungs.Conclusions:The observed problems of spirometry recording illustrate the challenges encountered when using spirometers as breathing surrogate for 4D CT acquisition. The high correlation between spirometry and bellows breathing signals and the verified factor of 1.11 between CT‐based air content and tidal volume mean that the bellows measurement (or other equivalent surrogates) can be reliably converted to tidal volume using the CT‐based air content, avoiding the need for a spirometer.
Biological effect of different IMRT delivery techniques: SMLC, DMLC, and helical tomotherapy
Authors: Shaikh Mubin , Burmeister Jay , Joiner Michael , Pandya Shalini , Zhao Bo , Liu Qiang 
Published: January 2010

Purpose:Intensity‐modulated radiotherapy (IMRT) is delivered using a variety of techniques with differing temporal dose characteristics. Spatial dose metrics are generally used to evaluate treatment plan quality. However, the use of this information alone neglects the effects of the significant differences in dose delivery duration and dose accumulation patterns, both of which can impact cell survival. This study uses the linear‐quadratic model with dose protraction corrections to evaluate the biological effectiveness of different IMRT delivery techniques, including fixed gantry IMRT in SMLC (step‐and‐shoot) and DMLC (sliding window) modes and a rotational IMRT technique (helical tomotherapy) for the treatment of prostate and head/neck sites.Methods:The temporal dose pattern was measured using a small volume ion chamber (A1SL—) to calculate the protraction factor, and biological equivalent dose (BED) was calculated for a range of repair half‐times and ratios. The treatment BED is compared to an ideal delivery of the target prescription dose, in which dose is delivered instantaneously , to evaluate loss in biological effectiveness due to protraction in delivery. In the case of a conventional prescription, the loss in biological effectiveness was further evaluated using published tumor control probability (TCP) data.Results:With SMLC and DMLC IMRT delivery, for both prostate and head/neck, the expected additional loss in BED is about 1% compared to 3D CRT, which corresponds to a predicted 2%–3% reduction in TCP. For tomotherapy, the prostate BED loss is smaller in comparison to 3D CRT; hence, the authors expect a TCP increase of the order of 2%–3%. The aforementioned differences are due to the dose accumulation time.Conclusions:While it is theoretically possible to compensate for changes in biologically effective dose, this would be hindered by large uncertainties in parameters used for such calculations; therefore, it is advantageous to irradiate target volume elements as rapidly as possible. The results of this study indicate that temporal dose delivery pattern is an important component in determining the biological effects of IMRT treatment.
Nonlinear registration of serial coronary CT angiography (CCTA) for assessment of changes in atherosclerotic plaque
Authors: Woo Jonghye , Dey Damini , Cheng Victor Y. , Hong Byung‐Woo , Ramesh Amit , Sundaramoorthi Ganesh , Nakazato Ryo , Berman Daniel S. , Germano Guido , Kuo C.‐C. Jay , Slomka Piotr J. 
Published: January 2010

Purpose: Coronary CT angiography (CCTA) is a high‐resolution three‐dimensional imaging technique for the evaluation of coronary arteries in suspected or confirmed coronary artery disease (CAD). Coregistration of serial CCTA scans would allow precise superimposition of images obtained at two different points in time, which could aid in recognition of subtle changes and precise monitoring of coronary plaque progression or regression. To this end, the authors aimed at developing a fully automatic nonlinear volume coregistration for longitudinal CCTA scan pairs.Methods: The algorithm combines global displacement and local deformation using nonlinear volume coregistration with a volume‐preserving constraint. Histogram matching of intensities between two serial scans is performed prior to nonlinear coregistration with dense nonparametric local deformation in which sum of squared differences is used as a similarity measure. The approximate segmentation of coronary arteries obtained from commercially available software provides initial anatomical landmarks for the coregistration algorithm that help localize and emphasize the structure of interest. To avoid possible bias caused by incorrect segmentation, the authors convolve the Gaussian kernel with the segmented binary coronary tree mask and define an extended weighted region of interest. A multiresolution approach is employed to represent coarse‐to‐fine details of both volumes and the energy function is optimized using a gradient descent method. The authors applied the algorithm in ten paired CCTA datasets (20 scans in total) obtained within from each other on a dual source CT scanner to monitor progression of CAD.Results: Serial CCTA coregistration was successful in 9/10 cases as visually confirmed. The global displacement and local deformation of target registration error obtained from four anatomical landmarks were and , respectively, and the inverse consistency error of local deformation was . The observer variability between two expert observers was .Conclusions: The proposed coregistration algorithm demonstrates potential to accurately register serial CCTA scans, which may allow direct comparison of calcified and noncalcified atherosclerotic plaque changes between the two scans.
Real‐time tumor tracking: Automatic compensation of target motion using the Siemens 160 MLC
Authors: Tacke Martin B. , Nill Simeon , Krauss Andreas , Oelfke Uwe 
Published: January 2010

Purpose:Advanced high quality radiation therapy techniques such as IMRT require an accurate delivery of precisely modulated radiation fields to the target volume. Interfractional and intrafractional motion of the patient's anatomy, however, may considerably deteriorate the accuracy of the delivered dose to the planned dose distributions. In order to compensate for these potential errors, a dynamic real‐time capable MLC control system was designed.Methods:The newly developed adaptive MLC control system contains specialized algorithms which are capable of continuous optimization and correction of the aperture of the MLC according to the motion of the target volume during the dose delivery. The algorithms calculate the new leaf positions based on target information provided online to the system. The algorithms were implemented in a dynamic target tracking control system designed for a Siemens 160 MLC™. To assess the quality of the new target tracking system in terms of dosimetric accuracy, experiments with various types of motion patterns using different phantom setups were performed. The phantoms were equipped with radiochromic films placed between solid water slabs. Dosimetric results of exemplary deliveries to moving targets with and without dynamic MLC tracking applied were compared in terms of the gamma criterion to the reference dose delivered to a static phantom.Results:Our measurements indicated that dose errors for clinically relevant two‐dimensional target motion can be compensated by the new control system during the dose delivery of open fields. For a clinical IMRT dose distribution, the gamma success rate was increased from 19% to 77% using the new tracking system. Similar improvements were achieved for the delivery of a complete IMRT treatment fraction to a moving lung phantom. However, dosimetric accuracy was limited by the system's latency of 400 ms and the finite leaf width of 5 mm in the isocenter plane.Conclusions:Different experimental setups representing different target tracking scenarios proved that the tracking concept, the new algorithms and the dynamic control system make it possible to effectively compensate for dose errors due to target motion in real‐time. These early results indicate that the method is suited to increasing the accuracy and the quality of the treatment delivery for the irradiation of moving tumors.
Quantification of breast density with dual energy mammography: An experimental feasibility study
Authors: Ducote Justin L. , Molloi Sabee 
Published: January 2010

Purpose:Breast density, the percentage of glandular breast tissue, has been shown to be a strong indicator of breast cancer risk. A quantitative method to measure breast density with dual energy mammography was investigated using physical phantoms.Methods:The dual energy mammography system used a tungsten anode x‐ray tube with a rhodium beam filter for low energy images and a copper beam filter for high energy images. Glandular and adipose equivalent phantoms of uniform thickness were used to calibrate a dual energy basis decomposition algorithm. Four different phantom studies were used to evaluate the technique. The first study consisted of phantoms with thicknesses of 2.5–8.5 cm in 0.5 cm steps with variable densities centered at a mean of 28%. The second study consisted of phantoms at a fixed thickness of 4.0 cm, which ranged in densities from 0% to 100% in increments of 12.5%. The third study consisted of 4.0 cm thick phantoms at densities of 25%, 50% and 75% each imaged at three areal sizes, approximately 62.5, 125, and , in order to assess the effect of breast size on density measurement. The fourth study consisted of step phantoms designed to more closely mimic the shape of a female breast with maximal thicknesses from 3.0 to 7.0 cm at a fixed density of 50%. All images were corrected for x‐ray scatter.Results:The RMS errors in breast density measurements were 0.44% for the variable thickness phantoms, 0.64% for the variable density phantoms, 2.87% for the phantoms of different areal sizes, and 4.63% for step phantoms designed to closely resemble the shape of a breast.Conclusions:The results of the phantom studies indicate that dual energy mammography can be used to measure breast density with an RMS error of approximately 5%.
Semiautomatic vessel wall detection and quantification of wall thickness in computed tomography images of human abdominal aortic aneurysms
Authors: Shum Judy , DiMartino Elena S. , Goldhammer Adam , Goldman Daniel H. , Acker Leah C. , Patel Gopal , Ng Julie H. , Martufi Giampaolo , Finol Ender A. 
Published: January 2010

Purpose:Quantitative measurements of wall thickness in human abdominal aortic aneurysms (AAAs) may lead to more accurate methods for the evaluation of their biomechanical environment.Methods:The authors describe an algorithm for estimating wall thickness in AAAs based on intensity histograms and neural networks involving segmentation of contrast enhanced abdominal computed tomography images. The algorithm was applied to ten ruptured and ten unruptured AAA image data sets. Two vascular surgeons manually segmented the lumen, inner wall, and outer wall of each data set and a reference standard was defined as the average of their segmentations. Reproducibility was determined by comparing the reference standard to lumen contours generated automatically by the algorithm and a commercially available software package. Repeatability was assessed by comparing the lumen, outer wall, and inner wall contours, as well as wall thickness, made by the two surgeons using the algorithm.Results:There was high correspondence between automatic and manual measurements for the lumen area ( and for ruptured and unruptured aneurysms, respectively) and between vascular surgeons ( and for ruptured and unruptured aneurysms, respectively). The authors’ automatic algorithm showed better results when compared to the reference with an average lumen error of 3.69%, which is less than half the error between the commercially available application Simpleware and the reference (7.53%). Wall thickness measurements also showed good agreement between vascular surgeons with average coefficients of variation of 10.59% (ruptured aneurysms) and 13.02% (unruptured aneurysms). Ruptured aneurysms exhibit significantly thicker walls than unruptured ones , .Conclusions:While further refinement is needed to fully automate the outer wall segmentation algorithm, these preliminary results demonstrate the method's adequate reproducibility and low interobserver variability.