bluuebunny/crossref_metadata_2025 huggingface dataset:
Dosimetric characteristics of a low‐kV intra‐operative x‐ray source: Implications for use in a clinical trial for treatment of low‐risk breast cancer
Authors: Ebert M. A. , Carruthers B.
Published: September 2003

The dosimetric characteristics of a low‐kV x‐ray device for performing intra‐operative irradiations, the Intrabeam (Photoelectron Corporation, Lexington, MA), are examined. Two dosimetric models are considered–an analytical model considering only the primary x‐ray beam, and a Monte Carlo model utilizing the EGSnrc code and a spherical simulation geometry. Both models prove reliable for verifying measured dose distributions for the device. The Monte Carlo model is necessary for examining spectral variations and the influence of inhomogeneities. The predictions of the Monte Carlo model are utilized to examine points of consideration for a multi‐center clinical trial using the Intrabeam in the intra‐operative, single fraction post‐resection treatment of low‐risk breast cancer. Predicted differences in radiological equivalence of breast tissue and water suggest a 3–5% underdose of breast tissue (in a 50 kV beam) when dose fall‐off data in water is used. A substantial dose enhancement in bone (i.e., ribs) adjacent to the treatment site is predicted though, based on published clinical data for radiation‐induced rib fracture, it is concluded that induction of radiation‐induced rib fracture would not pose a significant risk. Dose–volume changes with size of the treatment area (defined by the size of the resection volume) are examined indicating large variations in dose–volume characteristics across the range of possible “target” volumes.
Beta dose calculation in human arteries for various brachytherapy seed types
Authors: Lee Sung‐Woo
Published: September 2003

This dissertation explores beta dose profiles of microspheres packed in arteries, various source geometries of that can be used for therapeutic purposes, and dose backscatter factors for selected beta sources. A novel treatment method by injecting microspheres into feeding arteries of arteriovenous malformations (AVM) is under preclinical investigation. To optimize radiation dose to the clinically important area, i.e., arterial wall, preliminary dosimetric studies were needed. Monte Carlo calculations were performed for several geometries simulating arteries filled with microspheres packed by random packing methods. Arterial radii used in the simulation varied from 50 μm to 3 mm; microsphere radii varied from 10 μm to 0.7 mm. Dose varied significantly as a function of microsphere size, for constant arterial sizes. For the same sizes of arteries, significant dose increase was observed because of inter‐artery exposure for large arteries (>0.1 cm radius) filled with large microspheres (>0.03 cm radius). Dose increase between small arteries (<0.03 cm radius) was less significant. The dose profiles of prototype beta brachytherapy sources were calculated using MCNP 4C Monte Carlo code as well as dose point kernel (DPK) for selected cases. Dose profiles were similar to those for beta sources currently used indicating that can substitute for current sources for certain cases. The DPK and MCNP results matched closely. Backscattering of electrons is a prominent secondary effect in beta dosimetry. The backscattering is closely correlated with factors such as geometry of source and scattering material, and composition of scattering material. The backscattering factors were calculated for selected beta sources that are currently used as well as for other potentially useful sources. The factors were calculated as a function of distance from the interface between water and scatterers. These factors were fit by a simple function for future incorporation into a DPK code. Backscattering effect was significant for short distances from interfaces between water and scattering material.
Analysis of various beamlet sizes for IMRT with 6 MV Photons
Authors: Sohn Jason W. , Dempsey James F. , Suh Tae S. , Low Daniel A.
Published: September 2003

Application of intensity modulated radiation therapy (IMRT) using multileaf collimation often requires the use of small beamlets to optimize the delivered radiation distribution. Small‐beam dose distribution measurements were compared to dose distributions calculated using a commercial treatment planning system that models its data acquired using measurements from relatively large fields. We wanted to evaluate only the penumbra, percent depth‐dose (PDD) and output model, so we avoided dose distribution features caused by rounded leaf ends and interleaf leakage by making measurements using the secondary collimators. We used a validated radiochromic film dosimetry system to measure high‐resolution dose distributions of 6 MV photon beams. A commercial treatment planning system using the finite size pencil beam (FSPB) dose calculation algorithm was commissioned using measured central axis outputs from 4.0×4.0 to 40.0×40.0 cm2 beams and radiographic‐film profile measurements of a 4.0×4.0 cm2 beam at twice the depth of maximum dose Calculated dose distributions for square fields of 0.5×0.5 cm2, and 1.0×1.0 cm2, to 6.0×6.0 cm2, in 1.0×1.0 cm2, increments were compared against radiochromic film measurements taken with the film oriented parallel to the beam central axis in a water equivalent phantom. The PDD of the smaller field sizes exhibited behavior typical of small fields, namely a decrease in with decreasing field size. The FSPB accurately modeled the depth‐dose and central axis output for depths deeper than the nominal of 1.5 cm plus 0.5 cm. The dose distribution in the build‐up and penumbra regions was not accurately modeled for depths less than 2 cm, especially for the fields of 2.0×2.0 cm2 and smaller. Using the γ function with 2 mm and 2% criteria, the dose model was shown to accurately predict the penumbra. While for single small beams the compared dose distributions passed the γ function criteria, the clinical appropriateness of these criteria is not clear for a composite IMRT plan. Further investigation of the cumulative impact of the observed dose discrepancies is warranted. We speculate that the observed differences in the penumbra regions arise from some energy dependent artifact in the radiographic‐film profiles used for commissioning. In the future, radiochromic film based commissioning might provide a more accurate data set for dose modeling.
Quantitative computerized analysis of diffuse lung disease in high‐resolution computed tomography
Authors: Uchiyama Yoshikazu , Katsuragawa Shigehiko , Abe Hiroyuki , Shiraishi Junji , Li Feng , Li Qiang , Zhang Chao‐Tong , Suzuki Kenji , Doi Kunio
Published: September 2003

An automated computerized scheme has been developed for the detection and characterization of diffuse lung diseases on high‐resolution computed tomography (HRCT) images. Our database consisted of 315 HRCT images selected from 105 patients, which included normal and abnormal slices related to six different patterns, i.e., ground‐glass opacities, reticular and linear opacities, nodular opacities, honeycombing, emphysematous change, and consolidation. The areas that included specific diffuse patterns in 315 HRCT images were marked by three radiologists independently on the CRT monitor in the same manner as they commonly describe in their radiologic reports. The areas with a specific pattern, which three radiologists marked independently and consistently as the same patterns, were used as “gold standard” for specific abnormal opacities in this study. The lungs were first segmented from the background in each slice by use of a morphological filter and a thresholding technique, and then divided into many contiguous regions of interest (ROIs) with a matrix. Six physical measures which were determined in each ROI included the mean and the standard deviation of the CT value, air density components, nodular components, line components, and multilocular components. Artificial neural networks (ANNs) were employed for distinguishing between seven different patterns which included normals and six patterns associated with diffuse lung disease. The sensitivity of this computerized method for a detection of the six abnormal patterns in each ROI was 99.2% (122/123) for ground‐glass opacities, 100% (15/15) for reticular and linear opacities, 88.0% (132/150) for nodular opacities, 100% (98/98) for honeycombing, 95.8% (369/385) for emphysematous change, and 100% (43/43) for consolidation. The specificity in detecting a normal ROI was 88.1% (940/1067). This computerized method may be useful in assisting radiologists in their assessment of diffuse lung disease in HRCT images.
Effect of saccharide additives on response of ferrous–agarose–xylenol orange radiotherapy gel dosimeters
Authors: Healy B. J. , Zahmatkesh M. H. , Nitschke K. N. , Baldock C.
Published: September 2003

Glucose, sucrose, starch, and locust bean gum have been used as additives to the ferrous–agarose–xylenol orange (FAX) gel dosimeter. The saccharide enhanced dosimeters were found to have a higher dose sensitivity over a standard FAX gel as measured by both optical density change and magnetic resonance imaging (MRI). With optical density measurement, OD‐dose sensitivity increases were up to 55% for glucose, 122% for sucrose and 43% for starch, while locust bean gum did not give a consistent response. With MRI, ‐dose sensitivity increases were up to 178% with sucrose addition. The FAX gel with sucrose was studied in greatest detail. The OD‐dose sensitivity dependence on cooling rate was reduced for the sucrose FAX gel over the standard FAX gel, which has significant implications for uniform dose sensitivity in large gel phantoms. The thermal oxidation rate in the sucrose FAX gel was up to 2.3 times higher than in the standard gel. The OD‐dose sensitivity of oxygenated sucrose FAX gels was 4.3 times greater than standard FAX gels, while continued enhancement in OD‐dose sensitivity with increased sucrose concentrations beyond 2.0 g/l was found only for the oxygenated sucrose FAX gels. Both the molar absorption coefficient of the ferric ion‐xylenol orange complex at 543 nm and gel pH were not affected by the presence of sucrose, with the implication that the higher OD‐dose sensitivity of gels with saccharides is due to increased chain reaction production of ferric ions.
A toolbox for intensity modulated radiation therapy optimization
Authors: Shepard D. M. , Jiang Z. , Earl M. A. , Ferris M. C. , Lim J. , Naqvi S.
Published: September 2003

We have designed a toolbox that provides an environment for testing radiotherapy optimization techniques, objective functions, and constraints. A set of three‐dimensional (3D) pencil beam dose distributions have been computed for a cylindrical phantom. The 6 MV pencil beams were computed using a superposition‐based dose engine commissioned for an Elekta SL20 linear accelerator. Due to the cylindrical symmetry of the phantom, the pencil beam dose distributions for any arbitrary beam angle can be determined by simply rotating the pencil beam data sets. Thus, the full accuracy is maintained without the need for additional dose calculations or large data storage requirements. In addition to the pencil beam data sets, tools are included for (1) rotating the pencil beams, (2) calculating the beam's eye view, (3) drawing structures, (4) writing the pencil beam dose data out to the optimizer, and (5) visualizing the optimized results. The pencil beam data sets and the corresponding tools are available for download at http://medschool.umaryland.edu/departments/radiationoncology/pencilbeam/. With this toolbox, researchers will have the ability to rapidly test new optimization techniques and formulations for intensity modulated radiation therapy and 3D conformal radiotherapy.
Development of dose calculation methods for brachytherapy treatment planning (in English)
Authors: Carlsson Tedgren Åsa K.
Published: September 2003

The aim of the thesis is to develop methods for improving accuracy in dose calculations for photon brachytherapy treatment planning. This is achieved by separating the total dose into its primary and scatter components and through the use of three‐dimensional integration methods to calculate the scatter dose. The collapsed‐cone kernel‐superposition algorithm, used clinically for treatment planning with external photon beams, was adapted for scatter‐dose calculations in brachytherapy. A successive‐scattering approach was developed to minimize the artifacts from the method's angular discretization of energy transport, which are otherwise a problem for the steep fluence gradients around brachytherapy sources. Methods for scaling kernels for heterogeneities, accounting for both photoelectric absorption and the emission of characteristic x rays, were derived. It is shown how data from a source‐characterization formalism, that separates the total dose into its primary and scatter components, can support the collapsed cone algorithm with the input required to model clinical sources. With the methods developed in this work, the collapsed cone algorithm can be used for three‐dimensional scatter dose calculations over the brachytherapy energy range, handle all heterogeneous materials and model clinical sources. An application in which this might be of particular importance is in designing individualized patient shields for intermediate energy isotopes such as and In this energy range (60–100 keV), thin foils of high atomic number effectively protect sensitive organs, however without three‐dimensional scatter‐dose calculations, errors as large as 10–20 % can occur within distances of therapeutic interest on the side targeted for treatment. Through use of the collapsed cone algorithm for scatter dose calculations, these dose reductions are predicted within 3% compared to the results of full‐scale Monte Carlo simulations.
Dual focal‐spot imaging for phase extraction in phase‐contrast radiography
Authors: Donnelly Edwin F. , Price Ronald R. , Pickens David R.
Published: September 2003

The purpose of this study was to evaluate dual focal spot imaging as a method for extracting the phase component from a phase‐contrast radiography image. All measurements were performed using a microfocus tungsten‐target x‐ray tube with an adjustable focal‐spot size (0.01 mm to 0.045 mm). For each object, high‐resolution digital radiographs were obtained with two different focal spot sizes to produce matched image pairs in which all other geometric variables as well as total exposure and tube kVp were held constant. For each image pair, a phase extraction was performed using pixel‐wise division. The phase‐extracted image resulted in an image similar to the standard image processing tool commonly referred to as “unsharp masking” but with the additional edge‐enhancement produced by phase‐contrast effects. The phase‐extracted image illustrates the differences between the two images whose imaging parameters differ only in focal spot size. The resulting image shows effects from both phase contrast as well as geometric unsharpness. In weakly attenuating materials the phase‐contrast effect predominates, while in strongly attenuating materials the phase effects are so small that they are not detectable. The phase‐extracted image in the strongly attenuating object reflects differences in geometric unsharpness. The degree of phase extraction depends strongly on the size of the smallest focal spot used. This technique of dual‐focal spot phase‐contrast radiography provides a simple technique for phase‐component (edge) extraction in phase‐contrast radiography. In strongly attenuating materials the phase‐component is overwhelmed by differences in geometric unsharpness. In these cases the technique provides a form of unsharp masking which also accentuates the edges. Thus, the two effects are complimentary and may be useful in the detection of small objects.
Accuracy of a simple method for deriving the presampled modulation transfer function of a digital radiographic system from an edge image
Authors: Buhr Egbert , Günther‐Kohfahl Susanne , Neitzel Ulrich
Published: September 2003

Several methods for accurately deriving the presampled modulation transfer function (MTF) of a pixelated detector from the image of a slightly slanted edge have been described in the literature. In this paper we report on a simple variant of the edge method that produces sufficiently accurate MTF values for frequencies up to the Nyquist frequency limit of the detector with little effort in edge alignment and computation. The oversampled ESF is constructed in a very simple manner by rearranging the pixel data of consecutive lines corresponding to a lateral shift of the edge by one pixel. A regular subsampling pitch is assumed for the oversampled ESF, which is given by the original pixel sampling distance divided by the integer number This allows the original data to be used for further computational analysis (differentiation and Fourier transform) without data preprocessing. Since the number of lines leading to an edge shift by one pixel generally is a fractional number rather than an integer, a systematic error may be introduced into the presampled MTF. Simulations and theoretical investigations show that this error is proportional to and increases with spatial frequency. For all frequencies up to the Nyquist limit, the relative error Δ MTF/MTF is smaller than . It can thus be kept below a given threshold by suitably selecting which furnishes a certain maximum edge angle. The method is especially useful for applications where the presampled MTF is needed only for frequencies up to the Nyquist frequency limit, such as the determination of the detective quantum efficiency (DQE).
Evaluation of the gamma dose distribution comparison method
Authors: Low Daniel A. , Dempsey James F.
Published: September 2003

The γ tool was developed to quantitatively compare dose distributions, either measured or calculated. Before computing γ, the dose and distance scales of the two distributions, referred to as evaluated and reference, are renormalized by dose and distance criteria, respectively. The renormalization allows the dose distribution comparison to be conducted simultaneously along dose and distance axes. The γ quantity, calculated independently for each reference point, is the minimum distance in the renormalized multidimensional space between the evaluated distribution and the reference point. The γ quantity degenerates to the dose‐difference and distance‐to‐agreement tests in shallow and very steep dose gradient regions, respectively. Since being introduced, the γ quantity has been used by investigators to evaluate dose calculation algorithms, and compare dosimetry measurements. This manuscript examines the γ distribution behavior in two dimensions and evaluates the γ distribution in the presence of data noise. Noise in the evaluated distribution causes the γ distribution to be underestimated relative to the no‐noise condition. Noise in the reference distribution adds noise in the γ distribution in proportion to the normalized dose noise. In typical clinical use, the fraction of points that exceed 3% and 3 mm can be extensive, so we typically use 5% and 2–3 mm in clinical evaluations. For clinical cases, the calculation time is typically 5 minutes for a interpolated resolution on an 800 MHz Pentium 4 for a radiographic film.
A reconstruction algorithm for coherent scatter computed tomography based on filtered back‐projection
Authors: van Stevendaal U. , Schlomka J.‐P. , Harding A. , Grass M.
Published: September 2003

Coherent scatter computed tomography (CSCT) is a reconstructive x‐ray imaging technique that yields the spatially resolved coherent‐scatter form factor of the investigated object. Reconstruction from coherently scattered x‐rays is commonly done using algebraic reconstruction techniques (ART). In this paper, we propose an alternative approach based on filtered back‐projection. For the first time, a three‐dimensional (3D) filtered back‐projection technique using curved 3D back‐projection lines is applied to two‐dimensional coherent scatter projection data. The proposed algorithm is tested with simulated projection data as well as with projection data acquired with a demonstrator setup similar to a multi‐line CT scanner geometry. While yielding comparable image quality as ART reconstruction, the modified 3D filtered back‐projection algorithm is about two orders of magnitude faster. In contrast to iterative reconstruction schemes, it has the advantage that subfield‐of‐view reconstruction becomes feasible. This allows a selective reconstruction of the coherent‐scatter form factor for a region of interest. The proposed modified 3D filtered back‐projection algorithm is a powerful reconstruction technique to be implemented in a CSCT scanning system. This method gives coherent scatter CT the potential of becoming a competitive modality for medical imaging or nondestructive testing.
On the use of C‐arm fluoroscopy for treatment planning in high dose rate brachytherapy
Authors: Liu Lizhong , Bassano Daniel A. , Prasad Satish C. , Keshler Bonnie L. , Hahn Seung S.
Published: September 2003

Treatment planning for brachytherapy requires the acquisition of geometrical information of the implant applicator and the patient anatomy. This is typically done using a simulator or a computed tomography scanner. In this study, we present a different method by which orthogonal images from a C‐arm fluoroscopic machine is used for high dose rate brachytherapy treatment planning. A typical C‐arm is not isocentric, and it does not have the mechanical accuracy of a simulator. One solution is to place a reconstruction box with fiducial markers around the patient. However, with the limited clearance of the C‐arm this method is very cumbersome to use, and is not suitable for all patients and implant sites. A different approach is adopted in our study. First, the C‐arm movements are limited to three directions only between the two orthogonal images: the C‐orbital rotation, the vertical column, and the horizontal arm directions. The amounts of the two linear movements and the geometric parameters of the C‐arm orbit are used to calculate the location of the crossing point of the two beams and thus the magnification factors of the two images. Second, the fluoroscopic images from the C‐arm workstation are transferred in DICOM format to the planning computer through a local area network. Distortions in the fluoroscopic images, with its major component the “pincushion” effect, are numerically removed using a software program developed in house, which employs a seven‐parameter polynomial filter. The overall reconstruction accuracy using this method is found to be 2 mm. This filmless process reduces the overall time needed for treatment planning, and greatly improves the workflow for high dose rate brachytherapy procedures. Since its commissioning nearly three years ago, this system has been used extensively at our institution for endobronchial, intracavitary, and interstitial brachytherapy planning with satisfactory results.
From physical dose constraints to equivalent uniform dose constraints in inverse radiotherapy planning
Authors: Thieke Christian , Bortfeld Thomas , Niemierko Andrzej , Nill Simeon
Published: September 2003

Optimization algorithms in inverse radiotherapy planning need information about the desired dose distribution. Usually the planner defines physical dose constraints for each structure of the treatment plan, either in form of minimum and maximum doses or as dose‐volume constraints. The concept of equivalent uniform dose (EUD) was designed to describe dose distributions with a higher clinical relevance. In this paper, we present a method to consider the EUD as an optimization constraint by using the method of projections onto convex sets (POCS). In each iteration of the optimization loop, for the actual dose distribution of an organ that violates an EUD constraint a new dose distribution is calculated that satisfies the EUD constraint, leading to voxel‐based physical dose constraints. The new dose distribution is found by projecting the current one onto the convex set of all dose distributions fulfilling the EUD constraint. The algorithm is easy to integrate into existing inverse planning systems, and it allows the planner to choose between physical and EUD constraints separately for each structure. A clinical case of a head and neck tumor is optimized using three different sets of constraints: physical constraints for all structures, physical constraints for the target and EUD constraints for the organs at risk, and EUD constraints for all structures. The results show that the POCS method converges stable and given EUD constraints are reached closely.
Re‐evaluation of the dose to the cyst wall in P‐32 radiocolloid treatments of cystic brain tumors using the Dose–Point–Kernel and Monte Carlo methods
Authors: Janicki Christian , Seuntjens Jan
Published: September 2003

Intracavity instillation of β‐emitting colloid pharmaceuticals is a common technique used to treat cystic brain tumors. Most of the dosimetric calculations that have been reported in the literature for this problem are based on empirical formulas derived by Loevinger. Concentration of P‐32 radiolabeled solution for the delivery of a prescribed dose (200 Gy to the cyst wall) has been published previously using this formalism in what we refer to as a standard nomogram. The calculations using the Loevinger formulas for calculating the P‐32 activity necessary to achieve 200 Gy at the cyst wall is re‐evaluated and compared to numerically computed results based on full Monte Carlo simulations (EGSnrc) and the dose–point–kernel (DPK) integration method. For cyst diameters greater than 1 cm, the new calculations agree well with previously published results (the standard nomogram) to within a few percents. However, for cyst diameters of less than 1 cm, it is shown that the standard nomogram results underestimate the therapeutic activity by a factor offor very small diametersNew tables based on our calculations are presented and the sources of discrepancies are identified. It is concluded that the new set of data based on our calculations should replace the standard nomogram to administer accurately the target dose to the cyst wall for the smaller diameter cysts
Dosimetry for radiocolloid therapy of cystic craniopharyngiomas
Authors: Leticia Rojas E. , Al‐Dweri Feras M. O. , Lallena Antonio M. , Bodineau Coral , Galán Pedro
Published: September 2003

The dosimetry for radiocolloid therapy of cystic craniopharyngiomas is investigated. Analytical calculations based on the Loevinger and the Berger formulas for electrons and photons, respectively, are compared with Monte Carlo simulations. The role of the material of which the colloid introduced inside the craniopharyngioma is made of as well as that forming the cyst wall is analyzed. It is found that the analytical approaches provide a very good description of the simulated data in the conditions where they can be applied (i.e., in the case of a uniform and infinite homogeneous medium). However, the consideration of the different materials and interfaces produces a strong reduction of the dose delivered to the cyst wall in relation to that predicted by the Loevinger and the Berger formulas.
Analytic modeling of breast elastography
Authors: Liu H. T. , Sun L. Z. , Wang G. , Vannier M. W.
Published: September 2003

The elastic moduli of tumors change during their pathological evolution. Elastographic imaging has potential for detecting and characterizing cancers by mapping the stiffness distribution in tissues. In this paper a micromechanics‐based analytical method was developed to detect the location, size, and elastic modulus of a tumor mass embedded in a symmetric two‐dimensional breast tissue. A closed‐form solution for the strain elastograms (forward problem) was derived. A computational algorithm for the inverse problem was developed for the detection, localization, and characterization of a heterogeneous mass embedded in a breast tissue. Numerical examples were presented to evaluate the proposed method's performance. The detectability of a tumor mass was estimated with respect to lesion location, size, and modulus contrast ratio. It was shown that the micromechanics theory provides a powerful tool for the diagnosis of breast cancer.
A stereotactic method for the three‐dimensional registration of multi‐modality biologic images in animals: NMR, PET, histology, and autoradiography
Authors: Humm J. L. , Ballon D. , Hu Y. C. , Ruan S. , Chui C. , Tulipano P. K. , Erdi A. , Koutcher J. , Zakian K. , Urano M. , Zanzonico P. , Mattis C. , Dyke J. , Chen Y. , Harrington P. , O'Donoghue J. A. , Ling C. C.
Published: September 2003

The objective of this work was to develop and then validate a stereotactic fiduciary marker system for tumor xenografts in rodents which could be used to co‐register magnetic resonance imaging (MRI), PET, tissue histology, autoradiography, and measurements from physiologic probes. A Teflon™ fiduciary template has been designed which allows the precise insertion of small hollow Teflon rods (0.71 mm diameter) into a tumor. These rods can be visualized by MRI and PET as well as by histology and autoradiography on tissue sections. The methodology has been applied and tested on a rigid phantom, on tissue phantom material, and finally on tumor bearing mice. Image registration has been performed between the MRI and PET images for the rigid Teflon phantom and among MRI, digitized microscopy images of tissue histology, and autoradiograms for both tissue phantom and tumor‐bearing mice. A registration accuracy, expressed as the average Euclidean distance between the centers of three fiduciary markers among the registered image sets, of was achieved between MRI and microPET image sets of a rigid Teflon phantom. The fiduciary template allows digitized tissue sections to be co‐registered with three‐dimensional MRI images with an average accuracy of 0.21 and 0.25 mm for the tissue phantoms and tumor xenografts, respectively. Between histology and autoradiograms, it was 0.19 and 0.21 mm for tissue phantoms and tumor xenografts, respectively. The fiduciary marker system provides a coordinate system with which to correlate information from multiple image types, on a voxel‐by‐voxel basis, with sub‐millimeter accuracy—even among imaging modalities with widely disparate spatial resolution and in the absence of identifiable anatomic landmarks.
Improved artificial neural networks in prediction of malignancy of lesions in contrast‐enhanced MR‐mammography
Authors: Vomweg T. W. , Buscema M. , Kauczor H. U. , Teifke A. , Intraligi M. , Terzi S. , Heussel C. P. , Achenbach T. , Rieker O. , Mayer D. , Thelen M.
Published: September 2003

The aim of this study was to evaluate the capability of improved artificial neural networks (ANN) and additional novel training methods in distinguishing between benign and malignant breast lesions in contrast‐enhanced magnetic resonance‐mammography (MRM). A total of 604 histologically proven cases of contrast‐enhanced lesions of the female breast at MRI were analyzed. Morphological, dynamic and clinical parameters were collected and stored in a database. The data set was divided into several groups using random or experimental methods [Training & Testing (T&T) algorithm] to train and test different ANNs. An additional novel computer program for input variable selection was applied. Sensitivity and specificity were calculated and compared with a statistical method and an expert radiologist. After optimization of the distribution of cases among the training and testing sets by the T & T algorithm and the reduction of input variables by the Input Selection procedure a highly sophisticated ANN achieved a sensitivity of 93.6% and a specificity of 91.9% in predicting malignancy of lesions within an independent prediction sample set. The best statistical method reached a sensitivity of 90.5% and a specificity of 68.9%. An expert radiologist performed better than the statistical method but worse than the ANN (sensitivity 92.1%, specificity 85.6%). Features extracted out of dynamic contrast‐enhanced MRM and additional clinical data can be successfully analyzed by advanced ANNs. The quality of the resulting network strongly depends on the training methods, which are improved by the use of novel training tools. The best results of an improved ANN outperform expert radiologists.
Beam orientation optimization for IMRT by a hybrid method of the genetic algorithm and the simulated dynamics
Authors: Hou Qing , Wang Jun , Chen Yan , Galvin James M.
Published: September 2003

We have developed a new method for beam orientation optimization in intensity‐modulated radiation therapy (IMRT). The problem of beam orientation optimization in IMRT is solved by a decoupled two‐step iterative process: (1) optimization of the intensity profiles for given beam configurations; (2) selection of optimal beam configurations based on the ranking by an objective function score for the results of the intensity profile optimization. The simulated dynamics algorithm is used for the intensity profile optimization. This algorithm enforces both the hard constraints and dose‐volume constraints. A genetic algorithm is used to select beam orientation configurations. The method has been tested for both a simulated and clinical case, and the results show that beam orientation optimization significantly improved IMRT plans within a time period that is clinically acceptable. The results also show the dependence of the optimal orientation configurations on the prescribed constraints. In addition, beam orientation optimization by the method described here can provide multiple plans with similar dose distributions. This degeneracy characteristic can be exploited to our advantage in introducing additional planning objectives, e.g., the smoothness of intensity profiles, for the selection of the optimal plan among the degenerate configurations for treatment delivery.
A quasiexact reconstruction algorithm for helical CT using a 3‐Pi acquisition
Authors: Bontus Claas , Köhler Thomas , Proksa Roland
Published: September 2003

Recently, an exact reconstruction method for helical CT was published by A. Katsevich. The algorithm is of the filtered backprojection type and is, therefore, computationally efficient. Moreover, during backprojection, only data are used which correspond to an illumination interval of 180° as seen from the object‐point. We propose a new reconstruction method, which is applicable to data obtained with a 3‐Pi acquisition [IEEE Trans. Med. Imaging 19, 848–863 (2000)]. The method uses the same filter types as the Katsevich algorithm, but the directions and the number of the filter lines are chosen differently. For the derivation of the new algorithm, we analyze the relationship of the Katsevich method and radon inversion. A certain radon plane can intersect with the backprojection interval related to a 3‐Pi acquisition either once, three, or five times. In analogy to the definition of quasiexactness introduced by Kudo et al. for a 1‐Pi acquisition, we use the term quasiexactness for algorithms on a 3‐Pi acquisition, if radon planes with one or three intersections within the backprojection interval are treated correctly. Using the results on the relationship with radon inversion, we can prove that our algorithm is quasiexact in this sense. We use simulation results in order to demonstrate that the algorithm yields excellent image quality.
Monte Carlo calculated TG‐43 dosimetry parameters for the SeedLink™ brachytherapy system
Authors: Medich David C. , Munro John J.
Published: September 2003

The SeedLink™ brachytherapy system is comprised from an assembly of I‐Plant™ 3500 interstitial brachytherapy seeds and bioresorbable spacers joined together by a 6‐mm‐long titanium sleeve centered over each seed. This device is designed to maintain specified spacing between seeds during treatment thereby decreasing implant preparation time and reducing radionuclide migration within the prostate and periprostatic region. Reliable clinical treatment and planning applications necessitate accurate dosimetric data for source evaluation, therefore the authors report the results of a Monte Carlo study designed to calculate the AAPM Task Group Report No. 43 dosimetric parameters for the SeedLink brachytherapy source and compare these values against previously published Monte Carlo study results of the I‐Plant 3500 brachytherapy seed. For this investigation, a total of source photon histories were processed for each set of in‐water and in‐air calculations using the MCNP4C2 Monte Carlo radiation transport code (RSICC). Statistically, the radial dose function, and the dose‐rate constant, Λ, were identical to the values calculated previously for the Model 3500 with the dose‐rate constant evaluated to be Λ=1.000±0.026 cGyh−1 U−1. The titanium sleeve used in SeedLink to bind together Model 3500 seeds and spacers resulted in slightly greater dosimetric anisotropy as exhibited in the anisotropy function, the anisotropy factor, and the anisotropy constant, which was calculated to be , or roughly 2% lower than the value calculated previously for the Model 3500. These results indicate that the radiological characteristics of the SeedLink dosimetry system are comparable to those obtained for previously characterized single seeds such as the Implant Sciences Model 3500 I‐Plant seed.
Modeling the instantaneous dose rate dependence of radiation diode detectors
Authors: Shi Jie , Simon William E. , Zhu Timothy C.
Published: September 2003

The sensitivity S of Si diodes generally increases with an increase in the instantaneous dose rate r of the radiation beam from clinical linear accelerators. A theoretical model is established to understand the physical origin of this dependence. During a radiation exposure, a portion of the excess minority carriers (electrons or holes) generated in the diode is captured by the R‐G (recombination‐generation) centers and is recombined with the majority carriers. The captured portion depends on the excess minority‐carrier concentration (proportional to r), the R‐G center concentration and the minority‐carrier capture cross‐sections for electrons and for holes) by the R‐G center. When r increases, the R‐G center concentration may not be sufficient to keep the recombination portion constant, which leads to an increase in diode sensitivity because a larger fraction of the charge will be collected. Larger majority‐carrier concentration increases the recombination probability of the excess minority carriers and thus decreases the r dependence. The ratio of minority‐carrier capture cross‐sections, influences the magnitude of the r dependence and also differentiates the r dependence between n‐type and p‐type diodes. A number of different circumstances can occur in diodes. When such as for the dominant R‐G center generated by electron radiation, the sensitivity is more dependent on r in an n‐type diode than in a p‐type diode if all the other device parameters are the same. When the sensitivity is then more dependent on r in a p‐type diode than in an n‐type diode. The condition of can occur when R‐G centers with this property are generated by the foundry die process. A diode could have very small r dependence due to large R‐G center concentration, generated by heavy platinum doping or radiation accumulated dose. Experimental data are compared with theory.
MLC dosimetric characteristics for small field and IMRT applications
Authors: Bayouth J. E. , Morrill S. M.
Published: September 2003

The objective of this work was to measure the performance characteristics of a double‐focus multileaf collimator (MLC) for intensity modulated radiation therapy (IMRT), specifically the variation in penumbra and leakage for narrow fields as a function of field position over a 20×27 cm space available for segmented MLC IMRT. Measurements were made with 6 MV x rays through a MLC containing 29 leaf pairs (27 pairs of 1 cm width), and EDR2 film at 10 cm depth in solid water at 100 cm SAD. Films were digitized with 0.17 mm resolution and converted to dose. Interleaf and intraleaf transmission were measured along 11 vertical profile locations. Leaf‐end transmission was measured along horizontal profiles for each of 9 different leaf abutments, traveling over a 20 cm range. In‐plane penumbra measurements were made through a single leaf retracted, for 7 different leaves. Cross‐plane penumbra (leaf‐end) measurements were made for all 27 leaf pairs, where the 1 cm field width was placed in 11 different off‐axis positions (20 cm range). Interleaf leakage (range 1.0%–1.5%), intraleaf transmission (range 0.6%–0.8%), and leaf‐end transmission (range 0.8%–2.7%) were consistent for all leaf pairs at a given abutment position. The penumbra for these 1‐cm‐wide fields was measured to be 0.36 cm±0.03 cm for 99% of the measurements. In conclusion, the penumbra and leakage of the double‐focus MLC were remarkably consistent for the range of leaf positions studied, producing dosimetric characteristics that are well suited for IMRT segments where opposing leaf pairs are often separated by 10 mm or less.
Dose correlation for thoracic motion in radiation therapy of breast cancer
Authors: Ding Meisong , Li Jinsheng , Deng Jun , Fourkal Eugene , Ma C.‐M.
Published: September 2003

This work investigates the dose correlation for deformed objects due to thoracic motion for radiotherapy treatment of breast cancer. An analytical model has been developed to reconstruct patient anatomy based on the assumption that the body will expand or compress proportionally during respiration. The patient geometry at any phase during a breathing pattern is reconstructed using the CT data taken at the inspiration and expiration phases and the breathing level which can be related to the measured chest wall motion. A correlation between the voxels in the inspiration (or expiration) geometry and the voxels in the reconstructed geometry at any phase of the breathing pattern is established so that the dose can be accumulated during a treatment. The method has been implemented for treatment planning dose calculation by interfacing with a Monte Carlo code. The patient geometry files for different phases of the breathing pattern are generated and the three‐dimensional dose data are obtained from the Monte Carlo simulations. The final dose distribution is reconstructed from the dose data at different breathing phases based on patient's breathing pattern associated with chest wall movements.
Virtual 3D IVUS vessel model for intravascular brachytherapy planning. I. 3D segmentation, reconstruction, and visualization of coronary artery architecture and orientation
Authors: Weichert Frank , Müller Heinrich , Quast Ulrich , Kraushaar Andreas , Spilles Peter , Heintz Martin , Wilke Carsten , von Birgelen Clemens , Erbel Raimund , Wegener Dietrich
Published: September 2003

Intravascular brachytherapy (IVB) can significantly reduce the risk of restenosis after interventional treatment of stenotic arteries, if planned and applied correctly. To facilitate computer‐based IVB planning, a three‐dimensional vessel model has been derived from information on coronary artery segments acquired by intravascular ultrasound (IVUS) and biplane angiography. Part I describes the approach of model construction and presents possibilities of visualization. The vessel model is represented by a voxel volume. Polygonal information about the vessel wall structure is derived by segmentation from a sequence of IVUS images automatically acquired ECG gated during pull back of the IVUS transducer. To detect horizontal, vertical, and radial contours, modified Canny‐Edge and Shen‐Castan filters are applied on Cartesian and polar coordinate representations of the IVUS tomograms as edge detectors. The spatial course of the vessel wall layers is traced in reconstructed longitudinal IVUS scans. By resampling the sequence of IVUS frames the voxel volume is obtained. For this purpose the frames are properly located in space and augmented with additional intermediate frames generated by interpolation. Their spatial location and orientation is derived from biplane X‐ray angiography which is performed simultaneously. For resampling, two approaches are proposed: insertion of the vertices of the rectangular goal grid into the cells of a deformed hexahedral mesh derived from the IVUS sequence, and insertion of the vertices of the hexahedral mesh into the cells of the rectangular grid. Finally, the vessel model is visualized by methods of combined volume and polygon rendering. The segmentation process is verified as being in good agreement with results obtained by manual contour tracing with a commercial system. Our approach of construction of the vessel model has been implemented into an interactive software system, 3D IVUS‐View, serving as the basis of a future system for intracoronary brachytherapy treatment planning being currently under development (Part II).
IMRT delivery verification using a spiral phantom
Authors: Richardson Susan L. , Tomé Wolfgang A. , Orton Nigel P. , McNutt Todd R. , Paliwal Bhudatt R.
Published: September 2003

In this paper we report on the testing and verification of a system for IMRT delivery quality assurance that uses a cylindrical solid water phantom with a spiral trajectory for radiographic film placement. This spiral film technique provides more complete dosimetric verification of the entire IMRT treatment than perpendicular film methods, since it samples a three‐dimensional dose subspace rather than using measurements at only one or two depths. As an example, the complete analysis of the predicted and measured spiral films is described for an intracranial IMRT treatment case. The results of this analysis are compared to those of a single field perpendicular film technique that is typically used for IMRT QA. The comparison demonstrates that both methods result in a dosimetric error within a clinical tolerance of 5%, however the spiral phantom QA technique provides a more complete dosimetric verification while being less time consuming. To independently verify the dosimetry obtained with the spiral film, the same IMRT treatment was delivered to a similar phantom in which LiF thermoluminescent dosimeters were arranged along the spiral trajectory. The maximum difference between the predicted and measured TLD data for the 1.8 Gy fraction was 0.06 Gy for a TLD located in a high dose gradient region. This further validates the ability of the spiral phantom QA process to accurately verify delivery of an IMRT plan.