bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fully automatic nonrigid registration‐based local motion estimation for motion‐corrected iterative cardiac CT reconstruction
Authors: Isola Alfonso A. , Grass Michael , Niessen Wiro J. 
Published: March 2010

Purpose:Cardiac computed tomography is a rapidly emerging technique for noninvasive diagnosis of cardiovascular diseases. Nevertheless, the cardiac motion continues to be a limiting factor. Electrocardiogram‐gated cardiac computed tomography reconstruction methods yield excellent results, but these are limited in their temporal resolution due to the mechanical movement of the gantry, and lead to residual motion blurring artifacts. If the motion of the cardiac region of interest is determined, motion compensated gated reconstructions can be applied to reduce motion artifacts. In this paper it is shown that elastic image registration methods can be an accurate solution to determine the cardiac motion. A method, which combines elastic registration and iterative computed tomography reconstruction methods delivering motion‐corrected images of a chosen cardiac region of interest, is introduced.Methods:Using a gated four‐dimensional region of interest image data set, a fully automatic elastic image registration is applied to recover a cardiac displacement field from a reference phase to a number of phases within the RR interval. Here, a stochastic optimizer and multiresolution approach are adopted to speed up the registration process. Subsequently, motion‐compensated iterative reconstruction using the determined motion field is carried out. For the image representation volume‐adapted spherical basis functions (blobs) are used to take the volume change caused by a divergent motion vector field into account.Results:The method is evaluated on phantom data and on four clinical data sets at a strong cardiac motion phase. Comparing the method to standard gated iterative reconstruction results shows that motion compensation strongly improves the image quality in these phases. A qualitative and quantitative accuracy study is presented for the estimated cardiac motion field. For the first time a blob‐volume adaptation is applied on clinical data, and in the case of divergent motion it yields improved image quality.Conclusions:A fully automatic local cardiac motion compensated gated iterative method with volume‐adapted blobs is proposed. The method leads to excellent motion‐corrected images which outperform nonmotion corrected results in phases of strong cardiac motion. In clinical cases, a volume‐dependent blob‐footprint adaptation proves to be a good solution to take care of the change in the blob volume caused by a divergent motion field.
Monte Carlo characterization of a new Yb‐169 high dose rate source for brachytherapy application
Authors: Cazeca Mario J. , Medich David C. , Munro John J. 
Published: March 2010

Purpose:The objective was to characterize a new Yb‐169 high dose rate source for brachytherapy application.Methods:Monte Carlo simulations were performed using theMCNP5 F6 energy deposition tallies placed around the Yb‐169 source at different radial distances in both air‐vacuum and water environments. The calculations were based on a spherical water phantom with a radius of 50 cm. The output from the simulations was converted into radial dose rate distribution in polar coordinates surrounding the brachytherapy source.Results:The results from Monte Carlo simulations were used to calculate the AAPM Task Group 43 dosimetric parameters: Anisotropy function, radial dose function, air kerma strength, and dose rate constant. The results indicate a dose rate constant of , anisotropy function ranging from 0.44 to 1.00 for radial distances of 0.5–10 cm and polar angles of 0°–180°.Conclusions:The data from the Yb‐169 HDR source, Model M42, presented in this study show that this source compares favorably with another source of Yb‐169, Model 4140, already approved for brachytherapy treatment.
Reference radiochromic film dosimetry in kilovoltage photon beams during CBCT image acquisition
Authors: Tomic Nada , Devic Slobodan , DeBlois François , Seuntjens Jan 
Published: March 2010

Purpose:A common approach for dose assessment during cone beam computed tomography (CBCT) acquisition is to use thermoluminescent detectors for skin dose measurements (on patients or phantoms) or ionization chamber (in phantoms) for body dose measurements. However, the benefits of a daily CBCT image acquisition such as margin reduction in planning target volume and the image quality must be weighted against the extra dose received during CBCT acquisitions.Methods:The authors describe a two‐dimensional reference dosimetry technique for measuring dose from CBCT scans using the on‐board imaging system on a Varian Clinac‐iX linear accelerator that employs the XR‐QA radiochromic film model, specifically designed for dose measurements at low energy photons. The CBCT dose measurements were performed for three different body regions (head and neck, pelvis, and thorax) using humanoid Rando phantom.Results:The authors report on both surface dose and dose profiles measurements during clinical CBCT procedures carried out on a humanoid Rando phantom. Our measurements show that the surface doses per CBCT scan can range anywhere between 0.1 and 4.7 cGy, with the lowest surface dose observed in the head and neck region, while the highest surface dose was observed for the Pelvis spot light CBCT protocol in the pelvic region, on the posterior side of the Rando phantom. The authors also present results of the uncertainty analysis of our XR‐QA radiochromic film dosimetry system.Conclusions:Radiochromic film dosimetry protocol described in this work was used to perform dose measurements during CBCT acquisitions with the one‐sigma dose measurement uncertainty of up to 3% for doses above 1 cGy. Our protocol is based on film exposure calibration in terms of “air kerma in air,” which simplifies both the calibration procedure and reference dosimetry measurements. The results from a full Monte Carlo investigation of the dose conversion of measured XR‐QA film dose at the surface into dose to water (or water kerma) at the surface of the phantom indicate that, for typical beam qualities used in CBCT, this conversion can be approximated by simple mass‐energy absorption coefficient ratios water‐to‐air.
Effective learning strategies for real‐time image‐guided adaptive control of multiple‐source hyperthermia applicators
Authors: Cheng Kung‐Shan , Dewhirst Mark W. , Stauffer Paul R. , Das Shiva 
Published: March 2010

Purpose:This paper investigates overall theoretical requirements for reducing the times required for the iterative learning of a real‐time image‐guided adaptive control routine for multiple‐source heat applicators, as used in hyperthermia and thermal ablative therapy for cancer.Methods:Methods for partial reconstruction of the physical system with and without model reduction to find solutions within a clinically practical timeframe were analyzed. A mathematical analysis based on the Fredholm alternative theorem (FAT) was used to compactly analyze the existence and uniqueness of the optimal heating vector under two fundamental situations: (1) noiseless partial reconstruction and (2) noisy partial reconstruction. These results were coupled with a method for further acceleration of the solution using virtual source (VS) model reduction. The matrix approximation theorem (MAT) was used to choose the optimal vectors spanning the reduced‐order subspace to reduce the time for system reconstruction and to determine the associated approximation error. Numerical simulations of the adaptive control of hyperthermia using VS were also performed to test the predictions derived from the theoretical analysis. A thigh sarcoma patient model surrounded by a ten‐antenna phased‐array applicator was retained for this purpose. The impacts of the convective cooling from blood flow and the presence of sudden increase of perfusion in muscle and tumor were also simulated.Results:By FAT, partial system reconstruction directly conducted in the full space of the physical variables such as phases and magnitudes of the heat sources cannot guarantee reconstructing the optimal system to determine the global optimal setting of the heat sources. A remedy for this limitation is to conduct the partial reconstruction within a reduced‐order subspace spanned by the first few maximum eigenvectors of the true system matrix. By MAT, this VS subspace is the optimal one when the goal is to maximize the average tumor temperature. When more than 6 sources present, the steps required for a nonlinear learning scheme is theoretically fewer than that of a linear one, however, finite number of iterative corrections is necessary for a single learning step of a nonlinear algorithm. Thus, the actual computational workload for a nonlinear algorithm is not necessarily less than that required by a linear algorithm.Conclusions:Based on the analysis presented herein, obtaining a unique global optimal heating vector for a multiple‐source applicator within the constraints of real‐time clinical hyperthermia treatments and thermal ablative therapies appears attainable using partial reconstruction with minimum norm least‐squares method with supplemental equations. One way to supplement equations is the inclusion of a method of model reduction.
Three‐dimensional quantitative evaluation method of nonrigid registration algorithms for adaptive radiotherapy
Authors: Rodriguez‐Vila B. , Gaya F. , Garcia‐Vicente F. , Gomez E. J. 
Published: March 2010

Purpose:Current radiotherapy is progressing to the concept of adaptive radiotherapy, which implies the adaptation of planning along the treatment course. Nonrigid registration is an essential image processing tool for adaptive radiotherapy and image guided radiotherapy, and the three‐dimensional (3D) nature of the current radiotherapy techniques requires a 3D quantification of the registration error that existing evaluation methods do not cover appropriately. The authors present a method for 3D evaluation of nonrigid registration algorithms’ performance, based on organ delineations, capable of working with near‐spherical volumes even in the presence of concavities.Methods:The evaluation method is composed by a volume shape description stage, developed using a newad hoc volume reconstruction algorithm proposed by the authors, and an error quantification stage. The evaluation method is applied to the organ delineations of prostate and seminal vesicles, obtained by an automatic segmentation method over images of prostate cancer patients treated with intensity modulated radiation therapy.Results:The volume reconstruction algorithm proposed has been shown to accurately model complex 3D surfaces by the definition of clusters of control points. The quantification method, inspired by the Haussdorf–Chebysev distance, provides a measure of the largest registration error per control direction, defining a valid metric for concave‐convex volumes. Summarizing, the proposed evaluation methodology presents accurate results with a high spatial resolution in a negligible computation time in comparison with the nonrigid registration time.Conclusions:Experimental results show that the metric selected for quantifying the registration error is of utmost importance in a quantitative evaluation based on measuring distances between volumes. The accuracy of the volume reconstruction algorithm is not so relevant as long as the reconstruction is tight enough on the actual volume of the organ. The new evaluation method provides a smooth and accurate volume reconstruction for both the reference and the registered organ, and a complete 3D description of nonrigid registration algorithms’ performance, resulting in a useful tool for study and comparison of registration algorithms for adaptive radiotherapy.
Evaluation of the spatial dependence of the point spread function in 2D PET image reconstruction using LOR‐OSEM
Authors: Wiant D. , Gersh J. A. , Bennett M. , Bourland J. D. 
Published: March 2010

Purpose:The use of positron emission tomography (PET) imaging has proved beneficial in the staging and diagnosis of several cancer disease sites. Additional applications of PET imaging in treatment planning and the evaluation of treatment response are limited by the relatively low spatial resolution of PET images. Including point spread function (PSF) information in the system matrix (SM) of iterative reconstruction techniques has been shown to produce improved spatial resolution in PET images.Methods:In this study, the authors sampled the spatially variant PSF at over 6000 locations in the field of view for a General Electric Discovery ST PET/CT (General Electric Healthcare, Waukesha, WI) scanner in 2D acquisition mode. The authors developed PSF blurred SMs based on different combinations of the radial, depth, and azimuthal spatial dependencies to test the overall spatial dependence of the PSF on image quality. The PSF blurred SMs were included in a LOR‐OSEM reconstruction algorithm and used for image reconstruction of geometric phantoms. The authors also examined the effect of sampling density on PSF characterization to design a more efficient sampling scheme.Results:The authors found that depth dependent change in the amplitude of the detector response was the most important factor affecting image quality. A SM created from a PSF that introduced (perpendicular to the LOR), (parallel to the LOR), or and dependent blurring across the radial lines of response led to visually identifiable improvements in spatial resolution and contrast in reconstructed images compared to images reconstructed with a purely geometric SM with no PSF blurring. Images reconstructed using a SM with and dependent blurring across the radial lines of response showed improved spatial resolution and contrast‐noise ratios compared to images reconstructed with a SM that had only dependent blurring. Additionally, the authors determined that the PSF could be adequately characterized with roughly 85% fewer samples through the use of a better optimized sampling scheme.Conclusions:PET image reconstruction using a SM made from an accurately characterized PSF that accounts for and dependencies results in improved spatial resolution and contrast‐noise relations, which may aid in lesion boundary detection for treatment planning or quantitative assessment of treatment response.
Intensity modulated proton therapy treatment planning using single‐field optimization: The impact of monitor unit constraints on plan quality
Authors: Zhu X. R. , Sahoo N. , Zhang X. , Robertson D. , Li H. , Choi S. , Lee A. K. , Gillin M. T. 
Published: March 2010

Purpose:To investigate the effect of monitor unit (MU) constraints on the dose distribution created by intensity modulated proton therapy (IMPT) treatment planning using single‐field optimization (SFO).Methods:Ninety‐four energies between 72.5 and 221.8 MeV are available for scanning beam IMPT delivery at our institution. The minimum and maximum MUs for delivering each pencil beam (spot) are 0.005 and 0.04, respectively. These MU constraints are not considered during optimization by the treatment planning system; spots are converted to deliverable MUs during postprocessing. Treatment plans for delivering uniform doses to rectangular volumes with and without MU constraints were generated for different target doses, spot spacings, spread‐out Bragg peak (SOBP) widths, and ranges in a homogeneous phantom. Four prostate cancer patients were planned with and without MU constraints using different spot spacings. Rounding errors were analyzed using an in‐house software tool.Results:From the phantom study, the authors have found that both the number of spots that have rounding errors and the magnitude of the distortion of the dose distribution from the ideally optimized distribution increases as the field dose, spot spacing, and range decrease and as the SOBP width increases. From our study of patient plans, it is clear that as the spot spacing decreases the rounding error increases, and the dose coverage of the target volume becomes unacceptable for very small spot spacings.Conclusions:Constraints on deliverable MU for each spot could create a significant distortion from the ideally optimized dose distributions for IMPT fields using SFO. To eliminate this problem, the treatment planning system should incorporate the MU constraints in the optimization process and the delivery system should reliably delivery smaller minimum MUs.
Prediction of stopping‐power ratios in flattening‐filter free beams
Authors: Ceberg Crister , Johnsson Stefan , Lind Mårten , Knöös Tommy 
Published: March 2010

Purpose:In recent years, there has been an increasing interest in flattening‐filter free (FFF) beams. However, since the removal of the flattening filter will affect both the mean and the variance of the energy spectrum, current beam‐quality specifiers may not be adequate for reference dosimetry in such beams. The purpose of this work was to investigate an alternative, more general beam‐quality specifier.Methods:The beam‐quality specifier used in this work was a combination of the kerma‐weighted mean and the coefficient of variation of the linear attenuation coefficient in water. These parameters can in theory be determined from narrow‐beam transmission measurements using a miniphantom “in‐air,” which is a measurement condition well suited also to small and nonstandard fields. The relation between the Spencer‐Attix stopping‐power ratios and this novel beam‐quality specifier was described by a simple polynomial. For reference, the authors used Monte Carlo calculated spectra and stopping‐power data for nine different beams, with and without flattening filter.Results:The polynomial coefficients were obtained by least‐squares optimization. For all beams included in this investigation, the average of the differences between the predicted and the Monte Carlo calculated stopping‐power ratios was (1 SD) (including TomoTherapy and CyberKnife example beams).Conclusions:An alternative dual‐parameter beam‐quality specifier was investigated. The evaluation suggests that it can be used successfully to predict stopping‐power ratios in FFF as well as conventional beams, regardless of filtration.
Attenuation‐emission alignment in cardiac PET/CT based on consistency conditions
Authors: Alessio Adam M. , Kinahan Paul E. , Champley Kyle M. , Caldwell James H. 
Published: March 2010

Purpose:In cardiac PET and PET/CT imaging, misaligned transmission and emission images are a common problem due to respiratory and cardiac motion. This misalignment leads to erroneous attenuation correction and can cause errors in perfusion mapping and quantification. This study develops and tests a method for automated alignment of attenuation and emission data.Methods:The CT‐based attenuation map is iteratively transformed until the attenuation corrected emission data minimize an objective function based on the Radon consistency conditions. The alignment process is derived from previous work by Welch et al. [“Attenuation correction in PET using consistency information,” IEEE Trans. Nucl. Sci. 45, 3134–3141 (1998)] for stand‐alone PET imaging. The process was evaluated with the simulated data and measured patient data from multiple cardiac ammonia PET/CT exams. The alignment procedure was applied to simulations of five different noise levels with three different initial attenuation maps. For the measured patient data, the alignment procedure was applied to eight attenuation‐emission combinations with initially acceptable alignment and eight combinations with unacceptable alignment. The initially acceptable alignment studies were forced out of alignment a known amount and quantitatively evaluated for alignment and perfusion accuracy. The initially unacceptable studies were compared to the proposed aligned images in a blinded side‐by‐side review.Results:The proposed automatic alignment procedure reduced errors in the simulated data and iteratively approaches global minimum solutions with the patient data. In simulations, the alignment procedure reduced the root mean square error to less than 5 mm and reduces the axial translation error to less than 1 mm. In patient studies, the procedure reduced the translation error by and resolved perfusion artifacts after a known misalignment for the eight initially acceptable patient combinations. The side‐by‐side review of the proposed aligned attenuation‐emission maps and initially misaligned attenuation‐emission maps revealed that reviewers preferred the proposed aligned maps in all cases, except one inconclusive case.Conclusions:The proposed alignment procedure offers an automatic method to reduce attenuation correction artifacts in cardiac PET/CT and provides a viable supplement to subjective manual realignment tools.
Technical Note: EGSnrc‐based dosimetric study of the BEBIG HDR brachytherapy sources
Authors: Selvam T. Palani , Bhola Subhalaxmi 
Published: March 2010

Purpose:The purpose of this work is to calculate two‐dimensional (2D) dose rate distributions around the BEBIG (Eckert & Ziegler, BEBIG GmbH, Germany) models GK60M21 (old) and Co0.A86 (new) high dose rate brachytherapy sources in an unbounded liquid water phantom. The study includes calculation of absorbed dose to water‐kerma ratio around the BEBIG sources and a point source in water. A comparison is made with previously published data.Methods:The EGSnrcMP Monte Carlo code system is used to calculate the absorbed dose and water‐kerma in water and air‐kerma strength in vacuum. EGSnrcMP‐based user codes such as EDKnrc, FLURZnrc, and DOSRZnrc are employed in the work.Results:The value of reaches a maximum of for the point source (constant between 3.6 and 4.5 mm from the source) and for the BEBIG sources (constant between 2.6 and 3.2 mm along the transverse axis of the sources). Dose rate data for the new and old sources are comparable to published data for radial distances . Differences up to 9% are observed at points close to the source . In addition for the new source, compared to previously published data, dose rate data are higher by 14% along the longitudinal axis where the source cable is connected. Dose rate differences on the longitudinal axis of this source are explained by varying the length of the simulated source cable.Conclusions:The 2D rectangular data set calculated in the present work could be considered for quality control on radiotherapy treatment planning systems.
Exposure to smoking in movies among British adolescents 2001–2006: Table 1
Authors: Anderson Stacey J , Millett Christopher , Polansky Jonathan R , Glantz Stanton A 
Published: March 2010

ObjectiveTo estimate youth exposure to smoking in movies in the UK and compare the likely effect with the USA.MethodsWe collected tobacco occurrences data for 572 top-grossing films in the UK screened from 2001 to 2006 and estimated the number of on-screen tobacco impressions delivered to British youths in this time period.Results91% of films in our sample that contained smoking were youth-rated films (British Board of Film Classification rating ‘15’ and lower), delivering at least 1.10 billion tobacco impressions to British youths during theatrical release. British youths were exposed to 28% more smoking impressions in UK youth-rated movies than American youth-rated movies, because 79% of movies rated for adults in the USA (‘R’) are classified as suitable for youths in the UK (‘15’ or ‘12A’).ConclusionBecause there is a dose-response relation between the amount of on-screen exposure to smoking and the likelihood that adolescents will begin smoking, the fact that there is substantially higher exposure to smoking in youth-rated films in the UK than in the USA suggests that the fraction of all youth smoking because of films in the UK is probably larger than in the USA. Other countries with ratings systems that are less conservative (in terms of language and sexuality) than the USA will also be likely to deliver more on-screen tobacco impressions to youths. Assigning an ‘18’ classification to movies that contain smoking would substantially reduce youth exposure to on-screen smoking and, hence, smoking initiation among British youths.