bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of radiograph‐based texture analysis and bone mineral density with three‐dimensional microarchitecture of trabecular bone
Authors: Ranjanomennahary P. , Ghalila S. Sevestre , Malouche D , Marchadier A. , Rachidi M. , Benhamou Cl. , Chappard C. 
Published: December 2010

Purpose:Hip fracture is a serious health problem and textural methods are being developed to assess bone quality. The authors aimed to perform textural analysis at femur on high‐resolution digital radiographs compared to three‐dimensional (3D) microarchitecture comparatively to bone mineral density.Methods:Sixteen cadaveric femurs were imaged with an x‐ray device using a C‐MOS sensor. One 17 mm square region of interest (ROI) was selected in the femoral head (FH) and one in the great trochanter (GT). Two‐dimensional (2D) textural features from the co‐occurrence matrices were extracted. Site‐matched measurements of bone mineral density were performed. Inside each ROI, a 16 mm diameter core was extracted. Apparent density and bone volume proportion were measured from a defatted bone core using Archimedes' principle. Microcomputed tomography images of the entire length of the core were obtained (Skyscan 1072®) at of resolution and usual 3D morphometric parameters were computed on the binary volume after calibration from . Then, bone surface/bone volume, trabecular thickness, trabecular separation, and trabecular number were obtained by direct methods without model assumption and the structure model index was calculated.Results:In univariate analysis, the correlation coefficients between 2D textural features and 3D morphological parameters reached 0.83 at the FH and 0.79 at the GT. In multivariate canonical correlation analysis, coefficients of the first component reached 0.95 at the FH and 0.88 at the GT.Conclusions:Digital radiographs, widely available and economically viable, are an alternative method for evaluating bone microarchitectural structure.
Development of a facility for high‐precision irradiation of cells with carbon ions
Authors: van Goethem Marc‐Jan , Niemantsverdriet Maarten , Brandenburg Sytze , Langendijk Johannes A. , Coppes Robert P. , van Luijk Peter 
Published: December 2010

Purpose:Compared to photons, using particle radiation in radiotherapy reduces the dose and irradiated volume of normal tissues, potentially reducing side effects. The biological effect of dose deposited by particles such as carbon ions, however, differs from that of dose deposited by photons. The inaccuracy in models to estimate the biological effects of particle radiation remains the most important source of uncertainties in particle therapy. Improving this requires high‐precision studies on biological effects of particle radiation. Therefore, the authors aimed to develop a facility for reproducible and high‐precision carbon‐ion irradiation of cells in culture. The combined dose nonuniformity in the lateral and longitudinal direction should not exceed ±1.5%. Dose to the cells from particles than other carbon ions should not exceed 5%.Methods:A uniform lateral dose distribution was realized using a single scatter foil and quadrupole magnets. A modulator wheel was used to create a uniform longitudinal dose distribution. The choice of beam energy and the optimal design of these components was determined usingGEANT4 and SRIM Monte Carlo simulations. Verification of the uniformity of the dose distribution was performed using a scintillating screen (lateral) and a water phantom (longitudinal). The reproducibility of dose delivery between experiments was assessed by repeated measurements of the spatial dose distribution. Moreover, the reproducibility of dose‐response measurements was tested by measuring the survival of irradiated HEK293 cells in three independent experiments.Results:The relative contribution of dose from nuclear reaction fragments to the sample was found to be when using 90 MeV/u carbon ions. This energy still allows accurate dosimetry conforming to the IAEA Report TRS‐398, facilitating comparison to dose‐effect data obtained with other radiation qualities. A 1.3 mm long spread‐out Bragg peak with a diameter of 30 mm was created, allowing the irradiation of cell samples with the specified accuracy. Measurements of the transverse and longitudinal dose distribution showed that the dose variation over the sample volume was ±0.8% and ±0.7% in the lateral and longitudinal directions, respectively. The track‐averaged LET of and dose‐averaged LET of at the position of the sample were obtained from a GEANT4 simulation, which was validated experimentally. Three separately measured cell‐survival curves yielded nearly identical results.Conclusions:With the new facility, high‐precision carbon‐ion irradiations of biological samples can be performed with highly reproducible results.
Fast image reconstruction for Compton camera using stochastic origin ensemble approach
Authors: Andreyev Andriy , Sitek Arkadiusz , Celler Anna 
Published: December 2010

Purpose:Compton camera has been proposed as a potential imaging tool in astronomy, industry, homeland security, and medical diagnostics. Due to the inherent geometrical complexity of Compton camera data, image reconstruction of distributed sources can be ineffective and/or time‐consuming when using standard techniques such as filtered backprojection or maximum likelihood‐expectation maximization (ML‐EM). In this article, the authors demonstrate a fast reconstruction of Compton camera data using a novel stochastic origin ensembles (SOE) approach based on Markov chains.Methods:During image reconstruction, the origins of the measured events are randomly assigned to locations on conical surfaces, which are the Compton camera analogs of lines‐of‐responses in PET. Therefore, the image is defined as an ensemble of origin locations of all possible event origins. During the course of reconstruction, the origins of events are stochastically moved and the acceptance of the new event origin is determined by the predefined acceptance probability, which is proportional to the change in event density. For example, if the event density at the new location is higher than in the previous location, the new position is always accepted. After several iterations, the reconstructed distribution of origins converges to a quasistationary state which can be voxelized and displayed.Results:Comparison with the list‐mode ML‐EM reveals that the postfiltered SOE algorithm has similar performance in terms of image quality while clearly outperforming ML‐EM in relation to reconstruction time.Conclusions:In this study, the authors have implemented and tested a new image reconstruction algorithm for the Compton camera based on the stochastic origin ensembles with Markov chains. The algorithm uses list‐mode data, is parallelizable, and can be used for any Compton camera geometry. SOE algorithm clearly outperforms list‐mode ML‐EM for simple Compton camera geometry in terms of reconstruction time. The difference in computational time will be much larger when full Compton camera system model, including resolution recovery, is implemented and realistic Compton camera geometries are used. It was also shown in this article that while correctly reconstructing the relative distribution of the activity in the object, the SOE algorithm tends to underestimate the intensity values and increase variance in the images; improvements to the SOE reconstruction algorithm will be considered in future work.
Reconstruction of brachytherapy seed positions and orientations from cone‐beam CT x‐ray projections via a novel iterative forward projection matching method
Authors: Pokhrel Damodar , Murphy Martin J. , Todor Dorin A. , Weiss Elisabeth , Williamson Jeffrey F. 
Published: December 2010

Purpose:To generalize and experimentally validate a novel algorithm for reconstructing the 3D pose (position and orientation) of implanted brachytherapy seeds from a set of a few measured 2D cone‐beam CT (CBCT) x‐ray projections.Methods:The iterative forward projection matching (IFPM) algorithm was generalized to reconstruct the 3D pose, as well as the centroid, of brachytherapy seeds from three to ten measured 2D projections. The gIFPM algorithm finds the set of seed poses that minimizes the sum‐of‐squared‐difference of the pixel‐by‐pixel intensities between computed and measured autosegmented radiographic projections of the implant. Numerical simulations of clinically realistic brachytherapy seed configurations were performed to demonstrate the proof of principle. An in‐house machined brachytherapy phantom, which supports precise specification of seed position and orientation at known values for simulated implant geometries, was used to experimentally validate this algorithm. The phantom was scanned on an ACUITY CBCT digital simulator over a full 660 sinogram projections. Three to ten x‐ray images were selected from the full set of CBCT sinogram projections and postprocessed to create binary seed‐only images.Results:In the numerical simulations, seed reconstruction position and orientation errors were approximately 0.6 mm and 5°, respectively. The physical phantom measurements demonstrated an absolute positional accuracy of or less. The and angle errors were found to be and , respectively, or less when using three projections; with six projections, results were slightly better. The mean registration error was better than 1 mm/6° compared to the measured seed projections. Each test trial converged in 10–20 iterations with computation time of 12–18 min/iteration on a 1 GHz processor.Conclusions:This work describes a novel, accurate, and completely automatic method for reconstructing seed orientations, as well as centroids, from a small number of radiographic projections, in support of intraoperative planning and adaptive replanning. Unlike standard back‐projection methods, gIFPM avoids the need to match corresponding seed images on the projections. This algorithm also successfully reconstructs overlapping clustered and highly migrated seeds in the implant. The accuracy of better than 1 mm and 6° demonstrates that gIFPM has the potential to support 2D Task Group 43 calculations in clinical practice.
Semiautomatic method to identify the best phase for gated RT in lung region by 4D‐PET/CT acquisitions
Authors: Mancosu Pietro , Danna Massimo , Bettinardi Valentino , Aquilina Mark Anthony , Lobefalo Francesca , Cozzi Luca , Fogliata Antonella , Scorsetti Marta 
Published: December 2010

Purpose: Delineating tumor motion by four‐dimensional positron emission tomography/computed tomography (4D‐PET/CT) is a crucial step for gated radiotherapy (RT). This article quantitatively evaluates semiautomatic algorithms for tumor shift estimation in the lung region due to patient respiration by 4D‐PET/CT, in order to support the selection of the best phases for gated RT, by considering the most stable phases of the breathing cycle.Methods: Three mobile spheres and ten selected lesions were included in this study. 4D‐PET/CT data were reconstructed and classified into six/ten phases. The semiautomatic algorithms required the generation of single sets of images representative of the full target motion, used as masks for segmenting the phases. For 4D‐CT, a pre‐established HU range was used, whereas three thresholds (100%, 80%, and 40%) were evaluated for 4D‐PET. By using these segmentations, the authors estimated the lesion motion from the shifting centroids, and the phases with the least motion were also deduced including the phases with a curve slope less than . The proposed algorithms were validated by comparing the results to those generated entirely by manual contouring.Results: In the phantom study, the mean difference between the manual contour and the semiautomatic technique was for 4D‐CT and for the 4D‐PET based on 40% threshold. In the patients' series, the mean difference was for 4D‐CT and for the 4D‐PET based on 40% threshold.Conclusions: Estimation of lesion motion by the proposed semiautomatic algorithm can be used to evaluate tumor motion due to breathing.
A TCP model incorporating setup uncertainty and tumor cell density variation in microscopic extension to guide treatment planning
Authors: Jin Jian‐Yue , Kong Feng‐Ming , Liu Dezhi , Ren Lei , Li Haisen , Zhong Hualiang , Movsas Benjamin , Chetty Indrin J. 
Published: December 2010

Purpose:Tumor control probability (TCP) models have been proposed to evaluate and guide treatment planning. However, they are usually based on the dose volume histograms (DVHs) of the planning target volume (PTV) and may not properly reflect the substantial variation in tumor burden from the gross tumor volume (GTV) to the microscopic extension (ME) and to the margin of PTV. In this study, the authors propose a TCP model that can account for the effects of setup uncertainties and tumor cell density decay in the ME region.Methods:The proposed TCP model is based on the total surviving clonogenic tumor cells (CTCs) after irradiation of a known dose distribution to a region with a CTC distribution. The CTC density was considered to be homogeneous within the GTV, while decreasing exponentially in the ME region. The effect of random setup uncertainty was modeled by convolving the dose distribution with a Gaussian probability density function, represented by a standard deviation,. The effect of systematic setup uncertainty was modeled by summing each calculated TCP for all potential offsets in a Gaussian probability, represented by . The model was then applied to simplified cases to demonstrate the concept. TCP dose responses were calculated for various GTV volumes, DVH shapes, CTC density decay coefficients, probabilities of lymph node metastasis, and random and systematic errors. The slopes of the dose falloff to cover the CTC density decay in the ME region and the margins to compensate setup errors were also analyzed in generalized cases.Results:The sigmoid TCP dose response curve shifted to the right substantially for a larger GTV, while modestly for cold spots in DVH. A dose distribution with a uniform dose within the GTV, and a linear dose falloff in the ME region, tended to cause a minimal TCP deterioration if a proper dose falloff slope was used. When the dose falloff slope was less steep than a critical slope represented by, the , which is the prescription dose at , and , which is the TCP slope at , varied little with different dose falloff slopes. However, both and deteriorated fast when the slopes were steeper than . The random setup error tended to shift the TCP curve to the right, while the systematic error tended to compress the curve downward. For combined random and systematic errors, we demonstrated that based on the model, a margin of added to the GTV was found to cause a TCP change corresponding to 2% drop at , or 0.5 Gy shift in .Conclusions:This study conceptually demonstrated that a TCP model incorporating the effects of tumor cell density variation and setup uncertainty may be used to guide radiation treatment planning.
Generalized equivalent field size for nonuniform fluence maps in IMRT dose calculation
Authors: Chen Mingli , Lu Weiguo 
Published: December 2010

Purpose:The equivalent field size (EFS) method is widely used to estimate dose of nonstandard fields, such as elongated or arbitrary shaped fields, for both central axis and off axis points. However, its application is limited to fluence maps with uniform intensity. In this work, we propose a generalized EFS (GEFS) for nonuniform fluence maps and present a formula for GEFS‐based dose calculation.Methods:A parallel‐beam dose table (PDT) consisting of central axis dose of circular fields of various diameters at various depths is used to define scatter contributions, based on which we calculate GEFS of any given fluence map. Such obtained GEFS, together with the radiological depth and PDT, is used to determine the dose at the point of interest. We tested GEFS‐based dose calculation on a water phantom for both uniform and nonuniform fluence maps and compared the results with those by the collapsed cone convolution/superposition (CCCS) method.Results:For all test cases, the gamma index is less than 1 based on the 3%/1 mm criteria for more than 96% of the calculated points. Larger discrepancies mainly occur along the field edges in the buildup region.Conclusions:A generalized equivalent field size for nonuniform fluence maps was proposed and its application in calculating dose at any point was presented and verified through comparison with the CCCS method.
Accelerated gradient based diffuse optical tomographic image reconstruction
Authors: Biswas Samir Kumar , Rajan K. , Vasu R. M. 
Published: December 2010

Purpose:Fast reconstruction of interior optical parameter distribution using a new approach called Broyden‐based model iterative image reconstruction (BMOBIIR) and adjoint Broyden‐based MOBIIR (ABMOBIIR) of a tissue and a tissue mimicking phantom from boundary measurement data in diffuse optical tomography (DOT).Methods:DOT is a nonlinear and ill‐posed inverse problem. Newton‐based MOBIIR algorithm, which is generally used, requires repeated evaluation of the Jacobian which consumes bulk of the computation time for reconstruction. In this study, we propose a Broyden approach‐based accelerated scheme for Jacobian computation and it is combined with conjugate gradient scheme (CGS) for fast reconstruction. The method makes explicit use of secant and adjoint information that can be obtained from forward solution of the diffusion equation. This approach reduces the computational time many fold by approximating the system Jacobian successively through low‐rank updates.Results:Simulation studies have been carried out with single as well as multiple inhomogeneities. Algorithms are validated using an experimental study carried out on a pork tissue with fat acting as an inhomogeneity. The results obtained through the proposed BMOBIIR and ABMOBIIR approaches are compared with those of Newton‐based MOBIIR algorithm. The mean squared error and execution time are used as metrics for comparing the results of reconstruction.Conclusions:We have shown through experimental and simulation studies that Broyden‐based MOBIIR and adjoint Broyden‐based methods are capable of reconstructing single as well as multiple inhomogeneities in tissue and a tissue‐mimicking phantom. Broyden MOBIIR and adjoint Broyden MOBIIR methods are computationally simple and they result in much faster implementations because they avoid direct evaluation of Jacobian. The image reconstructions have been carried out with different initial values using Newton, Broyden, and adjoint Broyden approaches. These algorithms work well when the initial guess is close to the true solution. However, when initial guess is far away from true solution, Newton‐based MOBIIR gives better reconstructed images. The proposed methods are found to be stable with noisy measurement data.
EPID‐guided 3D dose verification of lung SBRT
Authors: Aristophanous M. , Rottmann J. , Court L. E. , Berbeco R. I. 
Published: December 2010

Purpose:To investigate the feasibility of utilizing tumor tracks from electronic portal imaging device (EPID) images taken during treatment to verify the delivered dose.Methods:The proposed method is based on a computation of the delivered fluence by utilizing the planned fluence and the tumor motion track for each field. A phantom study was designed to assess the feasibility of the method. The CIRS dynamic thorax phantom was utilized with a realistic soft resin tumor, modeled after a real patient tumor. The dose calculated with the proposed method was compared to direct measurements taken with 15 metal oxide semiconductor field effect transistors (MOSFETs) inserted in small fissures made in the tumor model. The phantom was irradiated with the tumor static and moved with different range of motions and setup errors. EPID images were recorded throughout all deliveries and the tumor model was tracked post‐treatment with in‐house developed software. The planned fluence for each field was convolved with the tumor motion tracks to obtain the delivered fluence. Utilizing the delivered fluence from each field, the delivered dose was calculated. The estimated delivered dose was compared to the dose directly measured with the MOSFETs. The feasibility of the proposed method was also demonstrated on a real lung cancer patient, treated with stereotactic body radiotherapy.Results:The calculation of delivered dose with the delivered fluence method was in good agreement with the MOSFET measurements, with average differences ranging from 0.8% to 8.3% depending on the proximity of a dose gradient. For the patient treatment, the planned and delivered dose volume histograms were compared and verified the overall good coverage of the target volume.Conclusions:The delivered fluence method was applied successfully on phantom and clinical data and its accuracy was evaluated. Verifying each treatment fraction may enable correction strategies that can be applied during the course of treatment to ensure the desired dose coverage.
Monte Carlo investigation of charge‐transport effects on energy resolution and detection efficiency of pixelated CZT detectors for SPECT/PET applications
Authors: Myronakis Marios E. , Darambara Dimitra G. 
Published: December 2010

Purpose:Semiconductor detectors are increasingly considered as alternatives to scintillation crystals for nuclear imaging applications such as positron emission tomography (PET) or single photon emission computed tomography (SPECT). One of the most prominent detector materials is cadmium zinc telluride (CZT), which is currently used in several application‐specific nuclear imaging systems. In this work, the charge‐transport effects in pixelated CZT detectors in relation to detector pixel size and thickness are investigated for pixels sizes from 0.4 up to 1.6 mm.Methods:The determination of an optimum pixel size and thickness for use with photon energies of 140 and 511 keV, suitable for SPECT and PET studies, is attempted using photon detection efficiency and energy resolution as figures of merit. The Monte Carlo method combined with detailed finite element analysis was utilized to realistically model photon interactions in the detector and the signal generation process. TheGEANT4 Application for Tomographic Emission (GATE) toolkit was used for photon irradiation and interaction simulations. The COMSOL MULTIPHYSICS® software application was used to create finite element models of the detector that included charge drift, diffusion, trapping, and generation. Data obtained from the two methods were combined to generate accurate signal induction at the detector pixels. The energy resolution was calculated as the full width at half maximum of the energy spectrum photopeak. Photon detection efficiency was also calculated. The effects of charge transport within the detector and photon escape from primary pixel of interaction were investigated; the extent of diffusion to lateral pixels was also assessed.Results:Charge transport and signal induction were affected by the position of a pixel in the detector. Edge and corner pixels were less susceptible to lateral diffusion than pixels located in the inner part of the detector. Higher detection efficiency and increased photon escape from primary interaction pixel were observed for thicker detectors. Energy resolution achieved better values in 0.7 and 1.0 mm pixel size for 5 mm detector thickness and 1.6 mm pixel size for 10 mm thickness.Conclusions:Selection of pixel size and thickness depends on the imaging application and photon energy utilized. For systems that integrate two nuclear imaging modalities (i.e., combined SPECT/PET), the pixel size should offer an appropriate balance of the effects that take place in the detector, based on the results of the current work. This allows for a system to be designed with the same detector material and the same geometrical configuration for both modalities.